Chemistry (from Egyptian kēme (chem), meaning "earth"[1]) is the science that studies matter at the atomic to macromolecular scale, the reactions, transformations and aggregations of matter, as well as the energy and entropy released or absorbed during these processes. In short, chemistry studies molecules, crystals, and metals and is concerned with the composition and statistical properties of such structures, as well as their transformations and interactions to become materials encountered in everyday life. According to modern chemistry, the physical properties of materials are generally determined by their structure at the molecular or atomic scale, which is itself defined by interatomic electromagnetic forces, and laws of quantum mechanics and thermodynamics. Robert Boyle (1661), Antoine Lavoisier (1787), and John Dalton (1808) can be considered the three fathers of modern chemistry,[2] although other scientists have played a vastly important role, such as Dmitri Mendeleyev, Friedrich Woehler, and Hermann Staudinger, to name but a few.
Contents [hide]
1 Introduction
2 History
3 Etymology
4 Definitions
5 Subdisciplines
6 The nature and classifications of matter
6.1 Atoms
6.2 Elements
6.3 Compounds
6.4 Substance
6.5 Molecules
6.6 Ions and Salts
6.7 States of matter
7 Fundamental concepts and theories
7.1 Nomenclature
7.2 Chemical reactions
7.3 Chemical laws
7.4 Bonding
7.5 Quantum chemistry
8 Chemical industry
9 See also
9.1 Lists
9.2 Related topics
10 References
11 Further reading
11.1 Popular reading
11.2 Introductory undergraduate text books
11.3 Advanced Undergraduate-level or Graduate text books
12 Professional societies
13 External links
[edit] Introduction
Chemistry is often called the "central science" because it connects the other natural sciences, such as astronomy, physics, material science, biology, and geology.[3] These connections are formed through various sub-disciplines that utilize concepts from multiple scientific disciplines. For example, physical chemistry involves applying the principles of physics to materials at the atomic and molecular level. The precise nature of the theoretical connection that chemistry (along with the other so-called special sciences) has with physics is a matter of research in philosophy of science.
Chemistry pertains to the interactions of matter. These interactions may be between two material substances or between matter and energy, especially in conjunction with the First Law of Thermodynamics. Traditional chemistry involves interactions between substances in chemical reactions, where one or more substances become one or more other substances. Sometimes these reactions are driven by energetic (enthalpic) considerations, such as when two highly energetic substances such as elemental hydrogen and oxygen react to form the less energetic substance water. Chemists often use reaction equations to summarize a specific reaction. The chemical reaction between hydrogen and oxygen is shown in the following equation:
2 H2 + O2 → 2 H2O
The number of atoms on the left and the right of the arrow is always equal in chemical reactions. Other reactions are driven primarily by entropy, which, simply stated, is a measure of disorder. Chemical reactions may be facilitated by a catalyst, which is generally another chemical substance present within the reaction media but unconsumed (such as sulfuric acid catalyzing the electrolysis of water) or a non-material phenomenon (such as electromagnetic radiation in photochemical reactions). Traditional chemistry also deals with the analysis of chemicals both in and apart from a reaction, as in spectroscopy.
Laboratory, Institute of Biochemistry, University of CologneAll ordinary matter consists of atoms or the subatomic components that make up atoms; protons, electrons and neutrons. Atoms may be combined to produce more complex forms of matter such as ions, molecules or crystals. The structure of the world we commonly experience and the properties of the matter we commonly interact with are determined by properties of chemical substances and their interactions. Steel is harder than iron because its atoms are bound together in a more rigid crystalline lattice. Wood burns or undergoes rapid oxidation because it can react spontaneously with oxygen in a chemical reaction above a certain temperature. Sugar and salt dissolve in water because their molecular/ionic properties allow this.
Substances tend to be classified in terms of their energy or phase as well as their chemical compositions. The three phases of matter at low energy are Solid, Liquid and Gas. Solids have fixed structures at room temperature which can resist gravity and other weak forces attempting to rearrange them, due to their tight bonds. Liquids have limited bonds, with no structure and flow with gravity. Gases have no bonds and act as free particles. Another way to view the three phases is by volume and shape: roughly speaking, solids have fixed volume and shape, liquids have fixed volume but no fixed shape, and gases have neither fixed volume nor fixed shape.
Water (H2O) is a liquid at room temperature because its molecules are bound by intermolecular forces called Hydrogen bonds. Thus, the forces between the molecules are so large that the energy at room temperature is not high enough to break them. Hydrogen sulfide (H2S) on the other hand is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions. The hydrogen bonds in water have enough energy to keep the water molecules from separating from each other but not from sliding around, making it a liquid at temperatures between 0 °C and 100 °C at sea level. Lowering the temperature or energy further, allows for a tighter organization to form, creating a solid, and releasing energy. Increasing the energy (see heat of fusion) will melt the ice although the temperature will not change until all the ice is melted. Increasing the temperature of the water will eventually cause boiling (see heat of vaporization) when there is enough energy to overcome the polar attractions between individual water molecules (100 °C at 1 atmosphere of pressure), allowing the H2O molecules to disperse enough to be a gas. Note that in each case there is energy required to overcome the intermolecular attractions and thus allow the molecules to move away from each other.
Scientists who study chemistry are known as chemists. Most chemists specialize in one or more sub-disciplines. The chemistry taught at the high school or early college level is often called "general chemistry" and is intended to be an introduction to a wide variety of fundamental concepts and to give the student the tools to continue on to more advanced subjects. Many concepts presented at this level are often incomplete and technically inaccurate, yet they are of extraordinary utility. Chemists regularly use these simple, elegant tools and explanations in their work because they have been proven to accurately model a very wide array of chemical reactivity, are generally sufficient, and more precise solutions may be prohibitively difficult to obtain.
The science of chemistry is historically a recent development but has its roots in alchemy which has been practiced for millennia throughout the world.
[edit] History
Robert Boyle - A founder of modern chemistry through use of controlled experiments, as contrasted with earlier rudimentary alchemical methodsSee also: History of chemistry, Alchemy, Nobel Prize in Chemistry, and Timeline of chemistry
The roots of chemistry can be traced to several phenomena. First is that of burning. This led to metallurgy. First, metals were purified from their ores, and later on alloys were created as a means of strengthening metals. This was a process that happened over thousands of years.
Gold had been purified long before the first alloys were created. However, the underlying process for purifying gold was not well understood. It was thought to be a transformation rather than purification. Many scholars in those days thought it reasonable to find a means for transforming cheaper (base) metals into gold. This led to the rise of alchemy, and the search for the Philosopher's Stone, believed to help create such a transformation.
Another force gave rise to alchemy: the plagues and blights that rocked Europe during what have been called the Dark Ages. This gave rise to a need for medicines. It was thought that there might exist a cure-all for all disease, called the Elixir of Life. However, like the Philosopher's Stone, neither one were ever found. Modern day chemistry states that such a medicine is not possible.
Alchemy for many was an avenue for charlatans to create fake medicines and counterfeit money. For others, it was an intellectual pursuit that could not separate superstition from scientific inquiry. Over time, practitioners got better at it. Paracelsus (1493-1541) rejected the 4-elemental theory and with only a vague understanding of his chemicals and medicines, formed a hybrid of alchemy and science in what was to be called iatrochemistry.
Following the influences of philosophers such as Sir Francis Bacon (1561-1626) and René Descartes (1596-1650), a scientific revolution ensued. These philosophers demanded more rigor in mathematics and in removing bias from scientific observations. In chemistry, this began with Robert Boyle (1627-1691), who discovered gases, and came up with equations that were known as Boyle's Law. The person celebrated as the Father of Chemistry was Antoine Lavoisier (1743-1794), who developed the theory of Conservation of mass in 1783. Equally important was the development of the Atomic Theory, principly by John Dalton (1766-1844) around 1800.
The discoveries of the chemical elements has a long history from the days of alchemy and culminating in the creation of the periodic table of the chemical elements by Dmitri Mendeleyev (1834-1907). The Nobel Prize in Chemistry created in 1901 gives an excellent overview of chemical discovery in the past 100 years.
[edit] Etymology
Main article: Chemistry (etymology)
The word chemistry comes from the earlier study of alchemy, which is basically the quest to make gold from earthen starting materials. As to the origin of the word "alchemy" the question is a debatable one; it certainly has Greek origins, and some, following E. Wallis Budge, have also asserted Egyptian origins. Alchemy, generally, derives from the old French alkemie and the Arabic al-kimia - "the art of transformation". The Arabs borrowed the word "kimia" from the Greeks when they conquered Alexandria in the year 642 AD. A tentative outline is as follows:
Egyptian alchemy [5,000 BC – 400 BC], formulate early "element" theories such as the Ogdoad.
Greek alchemy [332 BC – 642 AD], the Greek king Alexander the Great conquers Egypt and founds Alexandria, having the world's largest library, where scholars and "wise" men gather to study.
Arabian alchemy [642 AD – 1200], the Arabs take over Alexandria; Jabir is the main chemist
European alchemy [1300 – present], Pseudo-Geber builds on Arabic chemistry
Chemistry [1661], Boyle writes his classic chemistry text The Sceptical Chymist
Chemistry [1787], Lavoisier writes his classic Elements of Chemistry
Chemistry [1803], Dalton publishes his Atomic Theory
Thus, an alchemist was called a 'chemist' in popular speech, and later the suffix "-ry" was added to this to describe the art of the chemist as "chemistry".
[edit] Definitions
In retrospect, the definition of chemistry seems to invariably change per decade, as new discoveries and theories add to the functionality of the science. Shown below, for example, are some of the standard definitions used by various noted chemists:
Alchemy (330) – the study of the composition of waters, movement, growth, embodying and disembodying, drawing the spirits from bodies and bonding the spirits within bodies (Zosimos).[4]
Chymistry (1661) – the subject of the material principles of mixt bodies (Boyle).[5]
Chymistry (1663) – a scientifick art, by which one learns to dissolve bodies, and draw from them the different substances on their composition, and how to unite them again, and exalt them to an higher perfection (Glaser).[6]
Chemistry (1730) – the art of resolving mixt, compound, or aggregate bodies into their principles; and of composing such bodies from those principles (Stahl).[7]
Chemistry (1837) – the science concerned with the laws and effects of molecular forces (Dumas).[8]
Chemistry (1947) – the science of substances: their structure, their properties, and the reactions that change them into other substances (Pauling).[9]
Chemistry (1998) – the study of matter and the changes it undergoes (Chang).[10]
[edit] Subdisciplines
Lab pipettesChemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry.
Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. Analytical chemistry incorporates standardized experimental methods in chemistry. These methods may be used in all subdisciplines of chemistry, excluding purely theoretical chemistry.
Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms. Biochemistry and organic chemistry are closely related, as in medicinal chemistry or neurochemistry. Biochemistry is also associated with molecular biology and genetics.
Inorganic chemistry is the study of the properties and reactions of inorganic compounds. The distinction between organic and inorganic disciplines is not absolute and there is much overlap, most importantly in the sub-discipline of organometallic chemistry.
Organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. An organic compound is defined as any compound based on a carbon skeleton.
Physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. In particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. Important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, and spectroscopy. Physical chemistry has large overlap with molecular physics. Physical chemistry involves the use of calculus in deriving equations. It is usually associated with quantum chemistry and theoretical chemistry. Physical chemistry is a distinct discipline from chemical physics.
Theoretical chemistry is the study of chemistry via fundamental theoretical reasoning (usually within mathematics or physics). In particular the application of quantum mechanics to chemistry is called quantum chemistry. Since the end of the Second World War, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. Theoretical chemistry has large overlap with (theoretical and experimental) condensed matter physics and molecular physics. Essentially from reductionism theoretical chemistry is just physics, just like fundamental biology is just chemistry and physics.
Nuclear chemistry is the study of how subatomic particles come together and make nuclei. Modern Transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field.
Pure Chemistry - The study of chemistry for chemistry's sake.
Applied Chemistry - The study of chemistry directed at a goal possibly for money or military benefits.
Other fields include Astrochemistry, Atmospheric chemistry, Chemical Engineering, Chemo-informatics, Electrochemistry, Environmental chemistry, Flow chemistry, Geochemistry, Green chemistry, History of chemistry, Materials science, Medicinal chemistry, Molecular Biology, Molecular genetics, Nanotechnology, Organometallic chemistry, Petrochemistry, Pharmacology, Photochemistry, Phytochemistry, Polymer chemistry, Solid-state chemistry, Sonochemistry, Supramolecular chemistry, Surface chemistry, Immunochemistry and Thermochemistry.
[edit] The nature and classifications of matter
Chemistry - the study of atoms and the structures they can form together, such as Paclitaxel shown here
[edit] Atoms
Main article: Atom
An atom is a collection of matter consisting of a positively charged core (the atomic nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus. The Atom is also the smallest portion into which an element can be divided and still retain its properties, made up of a dense, positively charged nucleus surrounded by a system of electrons.
[edit] Elements
Main article: Chemical element
An element is a class of atoms which have the same number of protons in the nucleus. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.
The most convenient presentation of the chemical elements is in the periodic table of the chemical elements, which groups elements by atomic number. Due to its ingenious arrangement, groups, or columns, and periods, or rows, of elements in the table either share several chemical properties, or follow a certain trend in characteristics such as atomic radius, electronegativity, etc. Lists of the elements by name, by symbol, and by atomic number are also available. In addition, several isotopes of an element may exist.
[edit] Compounds
Main article: Chemical compound
A compound is a substance with a fixed ratio of chemical elements which determines the composition, and a particular organization which determines chemical properties. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one, with the oxygen between the hydrogens, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions.
[edit] Substance
Main article: Chemical substance
A chemical substance is a general term that can be an element, compound or a mixture of compounds, elements or compounds and elements. Most of the matter we encounter in our daily life are one or another kind of mixtures, e.g. air, alloys, biomass etc.
[edit] Molecules
Main article: Molecule
A molecule is the smallest indivisible portion of a pure compound or element that retains a set of unique chemical properties. Molecules differ from other chemical entities in that they can and often do exist as single electrically neutral units. Salts, for example, do not consist of molecular units but rather of many cations and anions in a crystal lattice. Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs.
[edit] Ions and Salts
Main article: Ion
An ion is a charged species, or an atom or a molecule that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na+) and negatively charged anions (e.g. chloride Cl−) can form neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH−) and phosphate (PO43−).
[edit] States of matter
Main article: Phase (matter)
In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.
Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions.
The most familiar examples of phases are solids, liquids, and gases. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. Even the familiar ice has many different phases, depending on the pressure and temperature of the system. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology.
[edit] Fundamental concepts and theories
[edit] Nomenclature
Main article: IUPAC nomenclature
Nomenclature refers to a system for naming chemical compounds. There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system. Inorganic compounds are named according to the inorganic nomenclature system. Nomenclature is a critical part of the language of chemistry and the IUPAC system of chemical nomenclature used today allows chemists to specify by name specific compounds amongst the infinite variety of possible chemicals.
[edit] Chemical reactions
Main article: Chemical reaction
A Chemical reaction is a process that results in the interconversion of chemical substances. Such reactions can result in molecules combining to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. For example, substances that react with oxygen to produce other substances are said to undergo oxidation; similarly a group of substances called acids or alkalis can react with one another to neutralize each other's effect, a phenomenon known as neutralization. Substances can also be dissociated or synthesized from other substances by various different chemical processes.
A stricter definition exists[11] that states "a Chemical Reaction is a process that results in the interconversion of chemical species". Under this definition, a chemical reaction may be an elementary reaction or a stepwise reaction. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events').
[edit] Chemical laws
Main article: Chemical law
The most fundamental concept in chemistry is the law of conservation of mass, which states that there is no detectable change in the quantity of matter during an ordinary chemical reaction. Modern physics shows that it is actually energy that is conserved, and that energy and mass are related; a concept which becomes important in nuclear chemistry. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.
Further laws of chemistry elaborate on the law of conservation of mass. Joseph Proust's law of definite composition says that pure chemicals are composed of elements in a definite formulation; we now know that the structural arrangement of these elements is also important.
Dalton's law of multiple proportions says that these chemicals will present themselves in proportions that are small whole numbers (i.e. 1:2 O:H in water); although in many systems (notably biomacromolecules and minerals) the ratios tend to require large numbers, and are frequently represented as a fraction. Such compounds are known as non-stoichiometric compounds.
[edit] Bonding
Main article: Chemical bond
Electron atomic and molecular orbitalsA chemical bond is the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. These potentials create the interactions which holds together atoms in molecules or crystals. In many simple compounds, Valence Bond Theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to predict molecular structure and composition. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory fails and alternative approaches, primarily based on principles of quantum chemistry such as the molecular orbital theory, are necessary. See diagram on electronic orbitals.
[edit] Quantum chemistry
Main article: Quantum chemistry
Quantum chemistry mathematically describes the fundamental behavior of matter at the molecular scale. It is, in principle, possible to describe all chemical systems using this theory. In practice, only the simplest chemical systems may realistically be investigated in purely quantum mechanical terms, and approximations must be made for most practical purposes (e.g., Hartree-Fock, post Hartree-Fock or Density functional theory, see computational chemistry for more details). Hence a detailed understanding of quantum mechanics is not necessary for most chemistry, as the important implications of the theory (principally the orbital approximation) can be understood and applied in simpler terms.
In quantum mechanics (several applications in computational chemistry and quantum chemistry), the Hamiltonian, or the physical state, of a particle can be expressed as the sum of two operators, one corresponding to kinetic energy and the other to potential energy. The Hamiltonian in the Schrödinger wave equation used in quantum chemistry does not contain terms for the spin of the electron.
Solutions of the Schrödinger equation for the hydrogen atom gives the form of the wave function for atomic orbitals, and the relative energy of say the 1s,2s,2p and 3s orbitals. The orbital approximation can be used to understand the other atoms e.g. helium, lithium and carbon.
[edit] Chemical industry
Main article: chemical industry
The chemical industry represents an important economic activity. The global top 50 chemical producers in 2004 had sales of 587 billion US dollars with a profit margin of 8.1% and research and development spending of 2.1% of total chemical sales.[12]
[edit] See also
[edit] Lists
Common chemicals - Where to find common chemical components
List of basic chemistry topics
List of chemistry topics
List of chemists
List of compounds
List of important publications in chemistry
Periodic Table of the Elements
Timeline of chemistry
Unsolved problems in chemistry
[edit] Related topics
Alchemy
Biochemistry
Chemical engineering
History of chemistry
Linus Pauling
Registration, Evaluation and Authorisation of Chemicals - A proposed European Union regulation
Perfection ("Perfection in physics and chemistry")
[edit] References
^ See: Chemistry (etymology) for possible origins of this word.
^ Mi Gyung, Kim (2003). Affinity, That Elusive Dream - A Genealogy of the Chemical Revolution. MIT Press. ISBN 0-262-11273-6.
^ Chemistry - The Central Science. The Chemistry Hall of Fame. York University. Retrieved on 2006-09-12.
^ Strathern, P. (2000). Mendeleyev’s Dream – the Quest for the Elements. New York: Berkley Books.
^ Boyle, Robert (1661). The Sceptical Chymist. New York: Dover Publications, Inc. (reprint). ISBN 0486428257.
^ Glaser, Christopher (1663). Traite de la chymie. as found in: Kim, Mi Gyung (2003). Affinity, That Elusive Dream - A Geanealogy of the Chemical Revolution. The MIT Press. ISBN 0-262-11273-6.
^ Stahl, George, E. (1730). Philosophical Principles of Universal Chemistry.
^ Dumas, J. B. (1837). 'Affinite' (lecture notes), vii, pg 4. “Statique chimique”, Paris: Academie des Sciences
^ Pauling, Linus (1947). General Chemistry. Dover Publications, Inc.. ISBN 0486656225.
^ Chang, Raymond (1998). Chemistry, 6th Ed.. New York: McGraw Hill. ISBN 0-07-115221-0.
^ Gold Book Link
^ (July 18, 2005) "Top 50 Chemical Producers". Chemical & Engineering News 83 (29): 20–23.
[edit] Further reading
[edit] Popular reading
Atkins, P.W. Galileo's Finger (Oxford University Press) ISBN 0198609418
Atkins, P.W. Atkins' Molecules (Cambridge University Press) ISBN 0521823978
Stwertka, A. A Guide to the Elements (Oxford University Press) ISBN 0195150279
[edit] Introductory undergraduate text books
Chang, Raymond. Chemistry 6th ed. Boston: James M. Smith, 1998. ISBN 0-07-115221-0.
Atkins, P.W., Overton, T., Rourke, J., Weller, M. and Armstrong, F. Shriver and Atkins inorganic chemistry (4th edition) 2006 (Oxford University Press) ISBN 0-19-926463-5
Clayden, J., Greeves, N., Warren, S., Wothers, P. Organic Chemistry 2000 (Oxford University Press) ISBN 0-19-850346-6
Voet and Voet Biochemistry (Wiley) ISBN 0-471-58651-X
[edit] Advanced Undergraduate-level or Graduate text books
Atkins, P.W. Physical Chemistry (Oxford University Press) ISBN 0-19-879285-9
Atkins, P.W. et al. Molecular Quantum Mechanics (Oxford University Press)
McWeeny, R. Coulson's Valence (Oxford Science Publications) ISBN 0-19-855144-4
Pauling, L. The Nature of the chemical bond (Cornell University Press) ISBN 0-8014-0333-2
Pauling, L., and Wilson, E. B. Introduction to Quantum Mechanics with Applications to Chemistry (Dover Publications) ISBN 0-486-64871-0
Stephenson, G. Mathematical Methods for Science Students (Longman)ISBN 0-582-44416-0
Smart and Moore Solid State Chemistry: An Introduction (Chapman and Hall) ISBN 0-412-40040-5
[edit] Professional societies
American Chemical Society
Chemical Institute of Canada
Chemical Society of Peru
International Union of Pure and Applied Chemistry
Royal Australian Chemical Institute
Royal Society of Chemistry
Society of Chemical Industry
World Association of Theoretical and Computational Chemists
[edit] External links
Find more information on Chemistry by searching Wikipedia's sister projects
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Textbooks from Wikibooks
Quotations from Wikiquote
Source texts from Wikisource
Images and media from Commons
News stories from Wikinews
Learning resources from Wikiversity
At Wikiversity you can learn more about chemistry at:
The School of Chemistry Chemistry Portal
International Union of Pure and Applied Chemistry
IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
Interactive Mind Map of Chemistry
Periodic Table: Ferocious Elements
For a full list of external links and suppliers see Wikipedia:Chemical sources
v • d • eChemistry[hide]
Analytical chemistry • Biochemistry • Bioinorganic chemistry • Chemical biology • Chemistry education • Click chemistry • Cluster chemistry • Computational chemistry • Electrochemistry • Environmental chemistry • Green chemistry • Inorganic chemistry • Materials science • Medicinal chemistry • Nuclear chemistry • Organic chemistry • Organometallic chemistry • Pharmacy • Pharmacology • Physical chemistry • Photochemistry • Polymer chemistry • Solid-state chemistry • Supramolecular chemistry • Theoretical chemistry • Thermochemistry • Wet chemistry
List of biomolecules • List of inorganic compounds • List of organic compounds • Periodic table
Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "knowledge") is the study of life. It is concerned with such topics as classifying the various forms of organisms, how species come into existence, and the interactions they have with each other and with the natural environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. However, together they address phenomena related to living organisms (biological phenomena) over a wide range of scales, from biophysics to ecology.
Many of the sub-disciplines of biology are ancient, such as botany, zoology, and medicine. However, biology as a unified science was first developed in the nineteenth century, as scientists discovered that all living things shared certain fundamental characteristics and were best studied as a whole. Today biology is one of the most prominent scientific fields. Over a million papers are published annually in a wide array of biology and medicine journals,[1] and biology is a standard subject of instruction at schools and universities around the world.
As such a vast field, biology is divided into a number of disciplines. The old divisions by type of organism remains with subjects such as botany encompassing the study of plants, zoology with the study of animals, and microbiology as the study of microorganisms. The field may also be divided based on the scale at which it is studied: molecular biology looks at the fundamental chemistry of life; cellular biology looks a the basic building block of all life, the cell; Physiology looks at the internal structure of organism; and ecology looks at how various organisms interrelate. Applied fields of biology such as medicine are more complex and involve many specialized sub-disciplines.
Contents [hide]
1 Principles
1.1 Universality
1.2 Evolution
1.3 Diversity
1.4 Continuity
1.5 Homeostasis
1.6 Interactions
2 Scope
2.1 Structure of life
2.2 Physiology of organisms
2.3 Diversity and evolution of organisms
2.3.1 Classification of life
2.4 Interactions of organisms
3 Etymology
4 History
5 See also
6 References
7 Further reading
8 External links
8.1 Journal links
[edit] Principles
Biology is a branch of science employing the scientific method to characterize and investigate knowledge. Scientific theories are based on scientific observations, and these theories are sometimes refined as new scientific information is compiled. Scientific theories can also be used to predict phenomena that has not yet been observed. Biological systems are sometimes statistically modeled, but as in other branches of science, theories are not always described using mathematics.
The biological sciences are characterized and unified by several major underlying principles and concepts: universality, evolution, diversity, continuity, genetics, homeostasis, and interactions.
However, biology is subject to the same physical laws that other branches of science obey, such as the laws of thermodynamics and conservation of mass.
[edit] Universality
Schematic representation of DNA, the primary genetic material.Main article: Life
While organisms may vary immensely in appearance, habitat, and behaviour it is a central principle of biology that all life shares certain universal fundamentals. A key feature is reproduction or replication. The entity being replicated, the replicator, in the past was considered to be the organism during the time of Darwin, but since the 1970s increasingly reduced to the scale of molecules.[2] All known life has a carbon-based biochemistry, carbon is the fundamental building block of the molecules that make up all known living things. Similarly water is the basic solvent for all known living organisms. While all these things are true of all organisms observed on Earth, in theory alternative forms of life could exist and some scientists do look at alternative biochemistry.
All terrestrial organisms use DNA and RNA-based genetic mechanisms to hold genetic information. Another universal principle is that all observed organisms with the exception of viruses are made of cells. Similarly, all organisms share common developmental processes.
[edit] Evolution
Main article: Evolution
A central organizing concept in biology is that all life has a common origin and has changed and developed through the process of the theory of evolution (see Common descent). This has led to the striking similarity of units and processes discussed in the previous section. Charles Darwin established evolution as a viable theory by articulating its driving force, natural selection (Alfred Russel Wallace is recognized as the co-discoverer of this concept). Darwin theorized that species and breeds developed through the processes of natural selection as well as by artificial selection or selective breeding.Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory.
The evolutionary history of a species— which describes the characteristics of the various species from which it descended— together with its genealogical relationship to every other species is called its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient organisms in paleontology. Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics (The major events in the evolution of life, as biologists currently understand them, are summarized on this evolutionary timeline).
Ever since its articulation by Darwin and Wallace, the theory of evolution by natural selection has come under attack by people who disagree with scientific findings or interpretations regarding the origins and diversity of life, generally favoring instead religious explanations. See Creation-evolution controversy for more information.
[edit] Diversity
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A phylogenetic tree of all living things, based on rRNA gene data, showing the separation of the three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.Classification is the province of the disciplines of systematics and taxonomy. Taxonomy places organisms in groups called taxa, while systematics seeks to define their relationships with each other. This classification technique has evolved to reflect advances in cladistics and genetics, shifting the focus from physical similarities and shared characteristics to phylogenetics.
Traditionally, living things have been divided into five kingdoms:
Monera -- Protista -- Fungi -- Plantae -- Animalia
However, many scientists now consider this five-kingdom system to be outdated. Modern alternative classification systems generally begin with the three-domain system:[3]
Archaea (originally Archaebacteria) -- Bacteria (originally Eubacteria) -- Eukaryota
These domains reflect whether the cells have nuclei or not, as well as differences in the cell exteriors.
Further, each kingdom is broken down continuously until each species is separately classified. The order is:
Kingdom
Phylum
Class
Order
Family
Genus
Species
The scientific name of an organism is obtained from its genus and species. For example, humans would be listed as Homo sapiens. Homo would be the genus and sapiens is the species. Whenever writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the species in lowercase; in addition the entire term would be put in italics or underlined. The term used for classification is called taxonomy.
There is also a series of intracellular parasites that are progressively "less alive" in terms of metabolic activity:
Viruses -- Viroids -- Prions
[edit] Continuity
Main article: Universal common descent
Up into the 19th century, it was commonly believed that life forms could appear spontaneously under certain conditions (see abiogenesis). This misconception was challenged by William Harvey's diction that "all life [is] from [an] egg" (from the Latin "Omne vivum ex ovo"), a foundational concept of modern biology. It simply means that there is an unbroken continuity of life from its initial origin to the present time.
A group of organisms shares a common descent if they share a common ancestor. All organisms on the Earth have been and are descended from a common ancestor or an ancestral gene pool. This last universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago. Biologists generally regard the universality of the genetic code as definitive evidence in favor of the theory of universal common descent (UCD) for all bacteria, archaea, and eukaryotes (see: origin of life).
[edit] Homeostasis
Main article: Homeostasis
Homeostasis is the ability of an open system to regulate its internal environment to maintain a stable condition by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit homeostasis. Homeostasis manifests itself at the cellular level through the maintenance of a stable internal acidity (pH); at the organismic level, warm-blooded animals maintain a constant internal body temperature; and at the level of the ecosystem, as when atmospheric carbon dioxide levels rise and plants are theoretically able to grow healthier and remove more of the gas from the atmosphere. Tissues and organs can also maintain homeostasis.
[edit] Interactions
Mutualistic symbiosis between clownfish of the genus Amphiprion that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protects the clown fish from its predators.Every living thing interacts with other organisms and its environment. One reason that biological systems can be difficult to study is that so many different interactions with other organisms and the environment are possible, even on the smallest of scales. A microscopic bacterium responding to a local sugar gradient is responding to its environment as much as a lion is responding to its environment when it searches for food in the African savannah. For any given species, behaviors can be co-operative, aggressive, parasitic or symbiotic. Matters become more complex when two or more different species interact in an ecosystem. Studies of this type are the province of ecology.
[edit] Scope
Main article: List of biology disciplines
Biology has become such a vast research enterprise that it is not generally regarded as a single discipline, but a number do assist in understanding the genetic variation of a population; and physiology borrows extensively from cell biology in describing the function of organ systems. Ethology and comparative psychology extend biology to the analysis of animal behavior and mental characteristics, whilst Evolutionary psychology proposes that the field of psychology, including in regard to humans, is a branch of biology.
[edit] Structure of life
Schematic of typical animal cell depicting the various organelles and structures.Main articles: Molecular biology, Cell biology, Genetics, and Developmental biology
Molecular biology is the study of biology at a molecular level. This field overlaps with other areas of biology, particularly with genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and learning how these interactions are regulated.
Cell biology studies the physiological properties of cells, as well as their behaviors, interactions, and environment. This is done both on a microscopic and molecular level. Cell biology researches both single-celled organisms like bacteria and specialized cells in multicellular organisms like humans.
Understanding cell composition and how they function is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important in the fields of cell and molecular biology. These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types.
Genetics is the science of genes, heredity, and the variation of organisms. In modern research, genetics provides important tools in the investigation of the function of a particular gene, or the analysis of genetic interactions. Within organisms, genetic information generally is carried in chromosomes, where it is represented in the chemical structure of particular DNA molecules.
Genes encode the information necessary for synthesizing proteins, which in turn play a large role in influencing (though, in many instances, not completely determining) the final phenotype of the organism.
Developmental biology studies the process by which organisms grow and develop. Originating in embryology, modern developmental biology studies the genetic control of cell growth, differentiation, and "morphogenesis," which is the process that gives rise to tissues, organs, and anatomy. Model organisms for developmental biology include the round worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, the zebrafish Brachydanio rerio, the mouse Mus musculus, and the weed Arabidopsis thaliana.
[edit] Physiology of organisms
Main articles: Physiology, Anatomy
Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Plant physiology also borrows techniques from both fields.
Anatomy is an important branch of physiology and considers how organ systems in animals, such as the nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. The study of these systems is shared with medically oriented disciplines such as neurology and immunology.
[edit] Diversity and evolution of organisms
In population genetics the evolution of a population of organisms is sometimes depicted as if travelling on a fitness landscape. The arrows indicate the preferred flow of a population on the landscape, and the points A, B, and C are local optima. The red ball indicates a population that moves from a very low fitness value to the top of a peak.Main articles: Evolutionary biology, Biodiversity, Botany, Zoology
Evolutionary biology is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomically-oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, or herpetology, but use those organisms as systems to answer general questions about evolution. Evolutionary biology is mainly based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution, as well as the developments in areas such as population genetics and evolutionary theory. In the 1990s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields which are often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy.
The two major traditional taxonomically-oriented disciplines are botany and zoology. Botany is the scientific study of plants. Botany covers a wide range of scientific disciplines that study the growth, reproduction, metabolism, development, diseases, and evolution of plant life. Zoology involves the study of animals, including the study of their physiology within the fields of anatomy and embryology. The common genetic and developmental mechanisms of animals and plants is studied in molecular biology, molecular genetics, and developmental biology. The ecology of animals is covered under behavioral ecology and other fields.
[edit] Classification of life
The dominant classification system is called Linnaean taxonomy, which includes ranks and binomial nomenclature. How organisms are named is governed by international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB). A fourth Draft BioCode was published in 1997 in an attempt to standardize naming in these three areas, but it has yet to be formally adopted. The Virus cInternational Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.
[edit] Interactions of organisms
A food web, a generalization of the food chain, depicting the complex interrelationships among organisms in an ecosystem.Main articles: Ecology, Ethology, Behavior, Biogeography
Ecology studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. The environment of an organism includes both its habitat, which can be described as the sum of local abiotic factors such as climate and ecology, as well as the other the organisms that share its habitat. Ecological systems are studied at several different levels, from individuals and populations to ecosystems and the biosphere. As can be surmised, ecology is a science that draws on several disciplines.
Ethology studies animal behavior (particularly of social animals such as primates and canids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book "The Expression of the Emotions in Man and Animals" influenced many ethologists.
Biogeography studies the spatial distribution of organisms on the Earth, focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics.
[edit] Etymology
Formed by combining the Greek βίος (bios), meaning 'life', and λόγος (logos), meaning 'study of', the word "biology" in its modern sense seems to have been introduced independently by Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and by Jean-Baptiste Lamarck (Hydrogéologie, 1802). The word itself is sometimes said to have been coined in 1800 by Karl Friedrich Burdach, but it appears in the title of Volume 3 of Michael Christoph Hanov's Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia, phytologia generalis et dendrologia, published in 1766.
[edit] History
Main articles: History of biology and History of medicine
Though the concept of biology as a single coherent field of knowledge only arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to the ancient Greeks (particularly Galen and Aristotle, respectively). During the Renaissance and Age of Discovery, renewed interest in empiricism as well as the rapidly increasing number of known organisms led to significant developments in biological thought; Vesalius inaugurated the rise of experimentation and careful observation in physiology, and a series of naturalists culminating with Linnaeus and Buffon began to create a conceptual framework for analyzing the diversity of life and the fossil record, as well as the development and behavior of plants and animals. The growing importance of natural theology—partly a response to the rise of mechanical philosophy—was also an important impetus for the growth of natural history (though it also further entrenched the argument from design).
In the 18th century many fields of science—including botany, zoology, and geology—began to professionalize, forming the precursors of scientific disciplines in the modern sense (though the process would not be complete until the late 1800s). Lavoisier and other physical scientists began to connect the animate and inanimate worlds through the techniques and theory of physics and chemistry. Into the 19th century, explorer-naturalists such as Alexander von Humboldt tried to elucidate the interactions between organisms and their environment, and the ways these relationships depend on geography—creating the foundations for biogeography, ecology and ethology. Many naturalists began to reject essentialism and seriously consider the possibilities of extinction and the mutability of species. These developments, as well as the results of new fields such as embryology and paleontology, were synthesized in Darwin's theory of evolution by natural selection. The end of the 19th century saw debates over spontaneous generation and the rise of the germ theory of disease and the fields of cytology, bacteriology and physiological chemistry, though the problem of inheritance was still a mystery.
In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics by Thomas Hunt Morgan and his students, and by the 1930s the combination of population genetics and natural selection led to the "neo-Darwinian synthesis" and the rise of the discipline of evolutionary biology. New biological disciplines developed rapidly, especially after Watson and Crick discovered the structure of DNA in 1953. Following the establishment of the Central Dogma and the cracking of the genetic code, biology was largely split between organismal biology—consisting of ecology, ethology, systematics, paleontology, evolutionary biology, developmental biology, and other disciplines that deal with whole organisms or groups of organisms—and the constellation of disciplines related to molecular biology—including cell biology, biophysics, biochemistry, neuroscience, immunology, and many other overlapping subjects. By the late 20th century, new fields like genomics and proteomics were reversing this trend; organismal biologists increasingly turned to molecular techniques and styles of thought, and molecular and cell biologists increasingly focused on the interplay between genes and the natural environment, as well as the genetic heterogeneity of natural populations such as humans.
Physics (Greek: φύσις (phúsis), "nature" and φυσικῆ (phusiké), "knowledge of nature") is the science concerned with the fundamental laws of the universe. Physics studies the elementary constituents of the universe—matter, energy, space, and time—and their interactions; it also analyzes systems best understood in terms of these fundamental principles. "Physics" (often spelled physike) formerly consisted of the study of its counterpart, natural philosophy, from classical times until the separation of modern physics from philosophy as a positive science during the nineteenth century.
The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability densityContents [hide]
1 Introduction
2 Theories
2.1 Classical and modern physics
2.2 Theories and concepts
3 Research
3.1 Theory and experiment
3.2 Subfields
4 History
4.1 The Scientific Revolution
4.2 Modern physics
4.3 Future directions
5 See also
5.1 Further reading
5.2 Organizations
6 Notes
7 External links
[edit] Introduction
Since antiquity, natural philosophers have sought to explain physical phenomena and the nature of matter, but the emergence of physics as a modern science began with the scientific revolution of the 16th and 17th centuries and continued through the dawn of modern physics in the early 20th century. The field has since continued to expand, with a growing body of research leading to discoveries such as the Standard Model of fundamental particles and a detailed history of the universe, along with revolutionary new technologies like nuclear weapons and semiconductors. Research today progresses on a vast array of topics, including high-temperature superconductivity, quantum computing, the Higgs boson, dark matter and dark energy, and the attempt to develop a theory of quantum gravity. Firmly grounded in observation and experiment, with a rich set of theories expressed in elegant mathematical language, physics has made a multitude of contributions to philosophy, science, and technology.
Discoveries in physics resonate throughout the natural sciences; physics has thus been described as the "fundamental science" because other fields such as chemistry and biology investigate systems whose properties are also based on the laws of physics.[1] Chemistry, for example, is the science of substances formed by atoms and molecules in bulk, but the properties of chemical compounds are determined by the physical properties of their underlying molecules.
The deepest visible-light image of the universe, the Hubble Ultra Deep FieldExperimental physics is closely related to engineering and technology. Experimental physicists involved in basic research design and perform experiments with particle accelerators, lasers, and other tools, whereas physicists involved in applied research invent technologies such as magnetic resonance imaging (MRI) and transistors.
Theoretical physics is closely related to mathematics, which provides the language of physical theories, and physicists often rely on numerical analysis and computer simulations. The fields of mathematical and computational physics are active areas of research. Theoretical physics often relates to philosophy and metaphysics when it deals with speculative ideas like multidimensional spaces and parallel universes.
[edit] Theories
Although physicists study a wide variety of phenomena, there are certain theories that are used by all physicists. Each of these theories has been tested in numerous experiments and proven to be a correct approximation of nature within its domain of validity. For example, the theory of classical mechanics accurately describes the motion of objects, provided that they are much larger than atoms and move much slower than the speed of light. While these theories have long been well-understood, they continue to be areas of active research—for example, a remarkable aspect of classical mechanics known as chaos was discovered in the 20th century, three centuries after its original formulation by Isaac Newton (1642–1727). The "central theories" are important tools for research into more specialized topics, and all physicists are expected to be literate in them.
Typical thermodynamic system - heat moves from hot (boiler) to cold (condenser) and work is extractedClassical mechanics is a model of the physics of forces acting upon bodies. It is often referred to as "Newtonian mechanics" after Newton and his laws of motion. Classical mechanics is subdivided into statics, which models objects at rest, kinematics, which models objects in motion, and dynamics, which models objects subjected to forces.
Electromagnetism is the physics of the electromagnetic field, a field that results from the presence and motion of charged particles and exerts forces on them. Electrodynamics describes the behavior of charged particles in electromagnetic fields. Light is a wave in the electromagnetic field that is radiated from accelerating charged particles. Aside from gravity, most of the forces in everyday experience are ultimately a result of electromagnetism.
Thermodynamics is the branch of physics that deals with the action of heat and the conversions from one to another of various forms of energy. Thermodynamics is particularly concerned with how these affect temperature, pressure, volume, mechanical action, entropy, and work. Statistical mechanics, a related theory, is the branch of physics that analyzes macroscopic systems by applying statistical principles to their microscopic constituents. It can be used to calculate the thermodynamic properties of bulk materials from the properties of individual molecules.
Relativity is a generalization of classical mechanics that describes fast-moving and very massive systems. It includes special and general relativity:
Special relativity is based on two postulates: (1) that the speed of light in a vacuum is constant and independent of the source or observer and (2) that the mathematical forms of the laws of physics are invariant in all inertial systems. It asserts an equivalence of mass and energy and a change in dimension, time, and effective mass with increased velocity.
General relativity extends special relativity to include transformations between non-inertial frames. It is formulated using differential geometry and interprets gravity as a distortion of spacetime caused by the presence of mass or energy.
Quantum mechanics generalizes classical mechanics to describe atomic and subatomic systems. It is based on the observation that all forms of energy are released in discrete units or bundles called quanta. Philosophers of physics continue to debate why quantum theory predicts only the statistical behavior of systems, even if they involve only a single particle. The discovery of quantum mechanics in the early 20th century revolutionized physics, and quantum mechanics is fundamental to most areas of current research.
[edit] Classical and modern physics
Further information: Classical physics, Quantum physics, Modern physics, Semiclassical
"Modern physics" refers to physics based on relativity and quantum theory, the two ideas that revolutionized the field in the early 20th century. Most of modern physics involves applications and extensions of quantum mechanics, so descriptions of the fundamental interactions that have not been quantized are referred to as "classical." Thus general relativity, Newtonian gravity, and the unquantized version of electromagnetism are classical theories. Phenomena which display only some aspects of quantum mechanics are often described using semiclassical models.
[edit] Theories and concepts
The table below lists many physical theories and the concepts they employ.
Theory Major subtopics Concepts
Classical mechanics Newton's laws of motion, Lagrangian mechanics, Hamiltonian mechanics, Kinematics, Statics, Dynamics, Chaos theory, Acoustics, Fluid dynamics, Continuum mechanics Density, Dimension, Gravity, Space, Time, Motion, Length, Position, Velocity, Acceleration, Galilean invariance, Mass, Momentum, Force, Energy, Angular momentum, Torque, Conservation law, Harmonic oscillator, Wave, Work, Power, Lagrangian, Hamiltonian, Tait-Bryan angles, Euler angles
Electromagnetism Electrostatics, Electrodynamics, Electricity, Magnetism, Maxwell's equations, Optics Capacitance, Electric charge, Current, Electrical conductivity, Electric field, Electric permittivity, Electric potential, Electrical resistance, Electromagnetic field, Electromagnetic induction, Electromagnetic radiation, Gaussian surface, Magnetic field, Magnetic flux, Magnetic monopole, Magnetic permeability
Thermodynamics and Statistical mechanics Heat engine, Kinetic theory Boltzmann's constant, Conjugate variables, Enthalpy, Entropy, Equation of state, Equipartition theorem, Free energy, Heat, Ideal gas law, Internal energy, Laws of thermodynamics, Maxwell relations, Irreversible process, Ising model, Mechanical action, Partition function, Pressure, Reversible process, Spontaneous process, State function, Statistical ensemble, Temperature, Thermodynamic equilibrium, Thermodynamic potential, Thermodynamic processes, Thermodynamic state, Thermodynamic system, Viscosity, Volume, Work, Granular material
Quantum mechanics Path integral formulation, Scattering theory, Schrödinger equation, Quantum field theory, Quantum statistical mechanics Adiabatic approximation, Blackbody radiation, Correspondence principle, Free particle, Hamiltonian, Hilbert space, Identical particles, Matrix Mechanics, Planck's constant, Observer effect, Operators, Quanta, Quantization, Quantum entanglement, Quantum harmonic oscillator, Quantum number, Quantum tunneling, Schrödinger's cat, Dirac equation, Spin, Wavefunction, Wave mechanics, Wave-particle duality, Zero-point energy, Pauli Exclusion Principle, Heisenberg Uncertainty Principle
Relativity Special relativity, General relativity, Einstein field equations Covariance, Einstein manifold, Equivalence principle, Four-momentum, Four-vector, General principle of relativity, Geodesic motion, Gravity, Gravitoelectromagnetism, Inertial frame of reference, Invariance, Length contraction, Lorentzian manifold, Lorentz transformation, Mass-energy equivalence, Metric, Minkowski diagram, Minkowski space, Principle of Relativity, Proper length, Proper time, Reference frame, Rest energy, Rest mass, Relativity of simultaneity, Spacetime, Special principle of relativity, Speed of light, Stress-energy tensor, Time dilation, Twin paradox, World line
[edit] Research
A magnet levitating above a high-temperature superconductor (with boiling liquid nitrogen underneath), demonstrating the Meissner effect — a phenomenon of importance to the field of condensed matter physicsContemporary research in physics is divided into several distinct fields.
Condensed matter physics is concerned with how the properties of bulk matter, such as the ordinary solids and liquids we encounter in everyday life, arise from the properties and mutual interactions of the constituent atoms. A topic of current interest is high-temperature superconductivity.
Atomic, molecular, and optical physics deals with small numbers of atoms and molecules, particularly with how they interact with light. A topic of current interest is the behavior of Bose-Einstein condensates.
Particle physics, also known as "high-energy physics", is concerned with the properties of submicroscopic particles much smaller than atoms, including elementary particles such as electrons, photons, and quarks. A topic of current interest is the search for the Higgs boson.
Astrophysics and cosmology apply the laws of physics to explain celestial phenomena, including stellar dynamics, black holes, galaxies, and the big bang. A topic of current interest is determining the nature of dark matter and dark energy.
Since the twentieth century, the individual fields of physics have become increasingly specialized, and today most physicists work in a single field for their entire careers. "Universalists" such as Albert Einstein (1879–1955) and Lev Landau (1908–1968), who worked in multiple fields of physics, are now very rare.
[edit] Theory and experiment
The culture of physics research differs from most sciences in the separation of theory and experiment. Since the twentieth century, most individual physicists have specialized in either theoretical physics or experimental physics. The great Italian physicist Enrico Fermi (1901–1954), who made fundamental contributions to both theory and experimentation in nuclear physics, was a notable exception. In contrast, almost all the successful theorists in biology and chemistry (e.g. American quantum chemist and biochemist Linus Pauling) have also been experimentalists, although this is changing as of late.
Roughly speaking, theorists seek to develop through abstractions and mathematical models theories that can both describe and interpret existing experimental results, and successfully predict future results, while experimentalists devise and perform experiments to explore new phenomena and test theoretical predictions. Although theory and experiment are developed separately, they are strongly dependent upon each other. Progress in physics frequently comes about when experimentalists make a discovery that existing theories cannot account for, necessitating the formulation of new theories. Likewise, ideas arising from theory often inspire new experiments. In the absence of experiment, theoretical research can go in the wrong direction; this is one of the criticisms that has been leveled against M-theory, a popular theory in high-energy physics for which no practical experimental test has ever been devised. Theorists working closely with experimentalists frequently employ phenomenology.
Applied physics is physics that is intended for a particular technological or practical use, as for example in engineering, as opposed to basic research. This approach is similar to that of applied mathematics. Applied physics is rooted in the fundamental truths and basic concepts of the physical sciences, but is concerned with the use of scientific principles in practical devices and systems, and in the application of physics in other areas of science. "Applied" is distinguished from "pure" by a subtle combination of factors such as the motivation and attitude of researchers and the nature of the relationship to the technology or science that may be affected by the work. [1]
[edit] Subfields
The table below lists many of the fields and subfields of physics along with the theories and concepts they employ.
Field Subfields Major theories Concepts
Astrophysics Cosmology, Gravitation physics, High-energy astrophysics, Planetary astrophysics, Plasma physics, Space physics, Stellar astrophysics Big Bang, Lambda-CDM model, Cosmic inflation, General relativity, Newton's law of universal gravitation Black hole, Cosmic background radiation, Cosmic string, Cosmos, Dark energy, Dark matter, Galaxy, Gravity, Gravitational radiation, Gravitational singularity, Planet, Solar system, Star, Supernova, Universe
Atomic, molecular, and optical physics Atomic physics, Molecular physics, Atomic and Molecular astrophysics, Chemical physics, Optics, Photonics Quantum optics, Quantum chemistry, Quantum information science Photon, Atom, Molecule, Diffraction, Electromagnetic radiation, Laser, Polarization, Spectral line, Casimir effect
Particle physics Nuclear physics, Nuclear astrophysics, Particle astrophysics, Particle physics phenomenology Standard Model, Quantum field theory, Quantum electrodynamics, Quantum chromodynamics, Electroweak theory, Effective field theory, Lattice field theory, Lattice gauge theory, Gauge theory, Supersymmetry, Grand unification theory, Superstring theory, M-theory Fundamental force (gravitational, electromagnetic, weak, strong), Elementary particle, Spin, Antimatter, Spontaneous symmetry breaking, Neutrino oscillation, Seesaw mechanism, Brane, String, Quantum gravity, Theory of everything, Vacuum energy
Condensed matter physics Solid state physics, High pressure physics, Low-temperature physics, Surface Physics,Nanoscale and Mesoscopic physics, Polymer physics BCS theory, Bloch wave, Fermi gas, Fermi liquid, Many-body theory Phases (gas, liquid, solid, Bose-Einstein condensate, superconductor, superfluid), Electrical conduction, Magnetism, Self-organization, Spin, Spontaneous symmetry breaking
Applied Physics Accelerator physics, Acoustics, Agrophysics, Biophysics, Chemical Physics, Communication Physics, Econophysics, Engineering physics, Fluid dynamics, Geophysics, Materials physics, Medical physics, Nanotechnology, Optics, Optoelectronics, Photovoltaics, Physical chemistry, Physics of computation, Plasma physics, Solid-state devices, Quantum chemistry, Quantum electronics, Quantum information science, Vehicle dynamics
[edit] History
Main article: History of physics
Further information: Famous physicists, Nobel Prize in physics
AristotleSince antiquity, people have tried to understand the workings of Nature and the behavior of matter: why unsupported objects drop to the ground, why different materials have different properties, and so forth. The character of the universe was also a mystery, for instance the earth and the behavior of celestial objects such as the sun and the moon. Several theories were proposed, most of which were incorrect, such as the earth orbiting the moon. These first theories were largely couched in philosophical terms, and never verified by systematic experimental testing, as is popular today. The works of Ptolemy and Aristotle were not always found to match everyday observations. There were exceptions and there are anachronisms - for example, Indian philosophers and astronomers gave many correct descriptions in atomism and astronomy, and the Greek mathematician Archimedes derived many correct quantitative descriptions of mechanics and hydrostatics.
Ibn al-Haitham (Alhazen)The willingness to question previously held truths and search for new answers eventually resulted in a period of major scientific advancements, now known as the Scientific Revolution of the late seventeenth century. The precursors to the scientific revolution may be traced back to the important developments made in India and Persia, including the elliptical model of the planets based on the heliocentric solar system of gravitation developed by Indian mathematician-astronomer Aryabhata; the basic ideas of atomic theory developed by Hindu and Jaina philosophers; the theory of light being equivalent to energy particles developed by the Indian Buddhist scholars Dignāga and Dharmakirti; the optical theory of light developed by Muslim scientist Ibn al-Haitham (Alhazen); the Astrolabe invented by the Persian astronomer Muhammad al-Fazari; and the significant flaws in the Ptolemaic system pointed out by Persian scientist Nasir al-Din Tusi.
[edit] The Scientific Revolution
As the influence of the Arab Empire expanded to Europe, the works of Aristotle, preserved by the Arabs, and the works of the Indians and Persians, became known in medieval Europe by the twelfth and thirteenth centuries.
Nicolaus Copernicus 1473-1543This eventually led to the scientific revolution, held by most historians (e.g., Howard Margolis) to have begun in 1543, when the first printed copy of Nicolaus Copernicus's De Revolutionibus was brought to the influential astronomer from Nuremberg (Nürnberg), where it had been printed by Johannes Petreius. Most of its contents had been written years prior, but the publication had been delayed. Copernicus died soon after receiving the copy.
GalileoFurther significant advances were made over the following century by Galileo Galilei, Christiaan Huygens, Johannes Kepler, and Blaise Pascal. During the early seventeenth century, Galileo pioneered the use of experimentation to validate physical theories, which is the key idea in modern scientific method. Galileo formulated and successfully tested several results in dynamics, in particular the Law of Inertia.
Sir Isaac NewtonThe scientific revolution is considered to have culminated with the publication of the Philosophiae Naturalis Principia Mathematica in 1687 by the mathematician, physicist, alchemist and inventor Sir Isaac Newton (1643-1727).In 1687, Newton published the Principia, detailing two comprehensive and successful physical theories: Newton's laws of motion, from which arise classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. Both theories agreed well with experiment. The Principia also included several theories in fluid dynamics.
From the late seventeenth century onward, thermodynamics was developed by physicist and chemist Boyle, Young, and many others. In 1733, Bernoulli used statistical arguments with classical mechanics to derive thermodynamic results, initiating the field of statistical mechanics. In 1798, Thompson demonstrated the conversion of mechanical work into heat, and in 1847 Joule stated the law of conservation of energy, in the form of heat as well as mechanical energy. Ludwig Boltzmann, in the nineteenth century, is responsible for the modern form of statistical mechanics.
Classical mechanics was re-formulated and extended by Leonhard Euler, French mathematician Joseph-Louis Comte de Lagrange, Irish mathematical physicist William Rowan Hamilton, and others, who produced new results in mathematical physics. The law of universal gravitation initiated the field of astrophysics, which describes astronomical phenomena using physical theories.
After Newton defined classical mechanics, the next great field of inquiry within physics was the nature of electricity. Observations in the seventeenth and eighteenth century by scientists such as Robert Boyle, Stephen Gray, and Benjamin Franklin created a foundation for later work. These observations also established our basic understanding of electrical charge and current.
The existence of the atom was proposed in 1808 by John Dalton.
James Clerk MaxwellIn 1821, the English physicist and chemist Michael Faraday integrated the study of magnetism with the study of electricity. This was done by demonstrating that a moving magnet induced an electric current in a conductor. Faraday also formulated a physical conception of electromagnetic fields. James Clerk Maxwell built upon this conception, in 1864, with an interlinked set of twenty equations that explained the interactions between electric and magnetic fields. These twenty equations were later reduced, using vector calculus, to a set of four equations by Oliver Heaviside.
In addition to other electromagnetic phenomena, Maxwell's equations also can be used to describe light. Confirmation of this observation was made with the 1888 discovery of radio by Heinrich Hertz and in 1895 when Wilhelm Roentgen detected X-rays.
[edit] Modern physics
Albert EinsteinThe ability to describe light in electromagnetic terms helped serve as a springboard for Albert Einstein's publication of the theory of special relativity in 1905. This theory combined classical mechanics with Maxwell's equations. The theory of special relativity unifies space and time into a single entity, spacetime. Relativity prescribes a different transformation between reference frames than classical mechanics; this necessitated the development of relativistic mechanics as a replacement for classical mechanics. In the regime of low (relative) velocities, the two theories agree. Einstein built further on the special theory by including gravity into his calculations, and published his theory of general relativity in 1915.
One part of the theory of general relativity is Einstein's field equation. This describes how the stress-energy tensor creates curvature of spacetime and forms the basis of general relativity. Further work on Einstein's field equation produced results which predicted the Big Bang, black holes, and the expanding universe. Einstein believed in a static universe. He tried, and failed, to fix his equation to allow for this. By 1929, however, Edwin Hubble's astronomical observations suggested that the universe is expanding at a possibly exponential rate.
Marie Sklodowska-CurieIn 1895, Röntgen discovered X-rays, which turned out to be high-frequency electromagnetic radiation.
Radioactivity was discovered in 1896 by Henri Becquerel, and further studied by Maria Sklodowska-Curie, Pierre Curie, and others. This initiated the field of nuclear physics.
In 1897, Joseph J. Thomson discovered the electron, the elementary particle which carries electrical current in circuits. In 1904, he proposed the first model of the atom, known as the plum pudding model. Its existence had been proposed in 1808 by John Dalton.
These discoveries revealed that the assumption of many physicists, that atoms were the basic unit of matter, was flawed, and prompted further study into the structure of atoms.
Ernest RutherfordIn 1911, Ernest Rutherford deduced from scattering experiments the existence of a compact atomic nucleus, with positively charged constituents dubbed protons. Neutrons, the neutral nuclear constituents, were discovered in 1932 by Chadwick. The equivalence of mass and energy (Einstein, 1905) was spectacularly demonstrated during World War II, as research was conducted by each side into nuclear physics, for the purpose of creating a nuclear bomb. The German effort, led by Heisenberg, did not succeed, but the Allied Manhattan Project reached its goal. In America, a team led by Fermi achieved the first man-made nuclear chain reaction in 1942, and in 1945 the world's first nuclear explosive was detonated at Trinity site, near Alamogordo, New Mexico.
In 1900, Max Planck published his explanation of blackbody radiation. This equation assumed that radiators are quantized, which proved to be the opening argument in the edifice that would become quantum mechanics. By introducing discrete energy levels, Planck, Einstein, Niels Bohr, and others developed quantum theories to explain various anomalous experimental results.
Erwin SchrödingerQuantum mechanics was formulated in 1925 by Heisenberg and in 1926 by Schrödinger and Paul Dirac, in two different ways, that both explained the preceding heuristic quantum theories. In quantum mechanics, the outcomes of physical measurements are inherently probabilistic; the theory describes the calculation of these probabilities. It successfully describes the behavior of matter at small distance scales. During the 1920s Schrödinger, Heisenberg, and Max Born were able to formulate a consistent picture of the chemical behavior of matter, a complete theory of the electronic structure of the atom, as a byproduct of the quantum theory.
Quantum field theory was formulated in order to extend quantum mechanics to be consistent with special relativity. It was devised in the late 1940s with work by Richard Feynman, Julian Schwinger, Sin-Itiro Tomonaga, and Freeman Dyson. They formulated the theory of quantum electrodynamics, which describes the electromagnetic interaction, and successfully explained the Lamb shift. Quantum field theory provided the framework for modern particle physics, which studies fundamental forces and elementary particles.
Chen Ning Yang and Tsung-Dao Lee, in the 1950s, discovered an unexpected asymmetry in the decay of a subatomic particle. In 1954, Yang and Robert Mills then developed a class of gauge theories which provided the framework for understanding the nuclear forces (Yang, Mills 1954). The theory for the strong nuclear force was first proposed by Murray Gell-Mann. The electroweak force, the unification of the weak nuclear force with electromagnetism, was proposed by Sheldon Lee Glashow, Abdus Salam, and Steven Weinberg and confirmed in 1964 by James Watson Cronin and Val Fitch. This led to the so-called Standard Model of particle physics in the 1970s, which successfully describes all the elementary particles observed to date.
Quantum mechanics also provided the theoretical tools for condensed matter physics, whose largest branch is solid state physics. It studies the physical behavior of solids and liquids, including phenomena such as crystal structures, semiconductivity, and superconductivity. The pioneers of condensed matter physics include Felix Bloch, who created a quantum mechanical description of the behavior of electrons in crystal structures in 1928. The transistor was developed by physicists John Bardeen, Walter Houser Brattain, and William Bradford Shockley in 1947 at Bell Laboratories.
The two themes of the twentieth century, general relativity and quantum mechanics, appear inconsistent with each other. General relativity describes the universe on the scale of planets and solar systems, while quantum mechanics operates on sub-atomic scales. This challenge is being attacked by string theory, which treats spacetime as composed, not of points, but of one-dimensional objects, strings. Strings have properties similar to a common string (e.g., tension and vibration). The theories yield promising, but not yet testable, results. The search for experimental verification of string theory is in progress.
The United Nations declared the year 2005, the centenary of Einstein's annus mirabilis, as the World Year of Physics.
[edit] Future directions
Main article: Unsolved problems in physics
Research in physics is progressing constantly on a large number of fronts, and is likely to do so for the foreseeable future.
In condensed matter physics, the greatest unsolved theoretical problem is the explanation for high-temperature superconductivity. Strong efforts, largely experimental, are being put into making workable spintronics and quantum computers.
In particle physics, the first pieces of experimental evidence for physics beyond the Standard Model have begun to appear. Foremost amongst these are indications that neutrinos have non-zero mass. These experimental results appear to have solved the long-standing solar neutrino problem in solar physics. The physics of massive neutrinos is currently an area of active theoretical and experimental research. In the next several years, particle accelerators will begin probing energy scales in the TeV range, in which experimentalists are hoping to find evidence for the Higgs boson and supersymmetric particles.
Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider; an experiment done in order to investigate the properties of a quark gluon plasma such as the one thought to exist in the ultrahot first few microseconds after the big bangTheoretical attempts to unify quantum mechanics and general relativity into a single theory of quantum gravity, a program ongoing for over half a century, have not yet borne fruit. Currently, the leading candidates are M-theory, superstring theory, and loop quantum gravity.
Many astronomical and cosmological phenomena have yet to be explained satisfactorily, including the existence of ultra-high energy cosmic rays, the baryon asymmetry, the acceleration of the universe, and the anomalous rotation rates of galaxies.
Although much progress has been made in high-energy, quantum, and astronomical physics, many everyday phenomena, involving complexity, chaos, or turbulence remain poorly understood. Complex problems that would appear to be soluble by a clever application of dynamics and mechanics, such as the formation of sand piles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, or self-sorting in shaken heterogeneous collections are unsolved.
These complex phenomena have received growing attention since the 1970s for several reasons, not least of which has been the availability of modern mathematical methods and computers, which enabled complex systems to be modeled in new ways. The interdisciplinary relevance of complex physics also has increased, as exemplified by the study of turbulence in aerodynamics, or the observation of pattern formation in biological systems. In 1932, Horace Lamb correctly prophesied the success of the theory of quantum electrodynamics and the near-stagnant progress in the study of turbulence:
I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.
[edit] See also
Physics Portal
[edit] Further reading
A large number of textbooks, popular books, and webpages about physics are available for further reading.
[edit] Organizations
AIP.org is the website of the American Institute of Physics
IOP.org is the website of the Institute of Physics
APS.org is the website of the American Physical Society
SPS National is the website of the American Society of Physics Students
[edit] Notes
^ The Feynman Lectures on Physics Volume I, Chapter III. Feynman, Leighton and Sands. ISBN 0-201-02115-3 For the philosophical issues of whether other sciences can be "reduced" to physics, see reductionism and special sciences.
Alpher, Herman, and Gamow. Nature 162,774 (1948). Wilson's 1978 Nobel lecture
C.S. Wu's contribution to the overthrow of the conservation of parity
Yang, Mills 1954 Physical Review 95, 631; Yang, Mills 1954 Physical Review 96, 191.
[edit] External links
Lecturefox Free University Lectures Physics