AskDefine | Define chemistry

Dictionary Definition



1 the science of matter; the branch of the natural sciences dealing with the composition of substances and their properties and reactions [syn: chemical science]
2 the way two individuals relate to each other; "their chemistry was wrong from the beginning -- they hated each other"; "a mysterious alchemy brought them together" [syn: interpersonal chemistry, alchemy]

User Contributed Dictionary



First coined 1605 < chemist < chymist < alchimista < الكيمياء < article al- + ''χυμεία < χύμα < χυμός < χέω.


  • /ˈkɛm.ɪ.stri/, /"kEm.I.stri/


  1. The branch of science that deals with the composition and constitution of substances and the changes that they undergo as a consequence of alterations in the constitution of their molecules.
  2. An application of chemical theory and method to a particular substance.
    the chemistry of iron
    the chemistry of indigo
  3. A treatise on chemistry.
  4. In the context of "informal": The mutual attraction between two people; rapport.
  5. In the context of "modifier": Relating to or using chemistry.
    a chemistry lesson

Usage notes

* This word and its derivatives were formerly spelled chy- or sometimes chi- (ie, chymistry, chymist, chymical, etc., or chimistry, chimist, chimical, etc.) with pronunciation depending on the spelling.


branch of science
  • Arabic: (al-kīmiya’)
  • Chinese:
    Mandarin: (huàxué)
  • Croatian: kemija
  • Czech: chemie
  • Danish: kemi
  • Finnish: kemia
  • German: Chemie
  • Greek: χημεία
  • Japanese: 化学 (かがく), (kagaku)
  • Polish: chemia
  • Portuguese: química
  • Swedish: kemi
application of chemical theory and method to a particular substance
  • Chinese:
    Mandarin: (huàxué)
  • Croatian: kemija
  • Danish: kemi , kemiske egenskab
  • Finnish: kemia
  • German: Chemie
  • Greek: χημεία
  • Japanese: 化学 かがく, (kagaku)
  • Portuguese: química
  • Swedish: kemi
treatise on chemistry
mutual attraction between two people
  • Chinese:
    Mandarin: (láidiàn)
  • Croatian: kemija
  • Danish: kemi
  • Finnish: vetovoima, kemia
  • German: Chemie
  • Polish: chemia
  • Portuguese: química
  • Swedish: kemi, personkemi
as modifier: relating to or using chemistry

Extensive Definition

One of the main characteristic of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.


A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state. This number is known as the Avogadro constant, and is determined empirically. The currently accepted value is 6.02214179(30) mol-1 (2007 CODATA). It is much like the term "a dozen" in that it is an absolute number (having no units) and can describe any type of elementary object, although the mole's use is usually limited to measurement of subatomic, atomic, and molecular structures.
The number of moles of a substance in one liter of a solution is known as its molarity. Molarity is the common unit used to express the concentration of a solution in physical chemistry.

Ions and salts

An ion is a charged species, 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 a crystalline lattice of 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−).
Ions in the gaseous phase is often known as plasma.


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. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. 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.

Chemical bond

A chemical bond is a concept for understanding how atoms stick together in molecules. It may be visualized as 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.

Chemical reaction

Chemical reaction is a concept related to the transformation of a chemical substance through its interaction with another, or as a result of its interaction with some form of energy. A chemical reaction may occur naturally or carried out in a laboratory by chemists in specially designed vessels which are often laboratory glassware. It can result in the formation or dissociation of molecules, that is, 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. Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.
A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.
The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction.
A stricter definition is that "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').


A chemical reaction is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light, thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exothermic if the final state is lower on the energy scale than the initial state; in case of endothermic reactions the situation is otherwise.
Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e^ - that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.
A related concept free energy, which incorporates entropy considerations too, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, \Delta G \le 0 \,; if it is equal to zero the chemical reaction is said to be at equilibrium.
There are only a limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in an higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive, that is amenable to chemical reactions.
The phase of a substance is invariably determined by its energy and those of its surroundings. When the intermolecular forces of a substance are such that energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H2O), a liquid at room temperature because its molecules are bound by hydrogen bonds. Whereas hydrogen sulfide (H2S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions.
The transfer of energy from one chemical substance to other depend on the size of energy quanta emitted from one substance. However, heat energy is easily transferred from almost any substance to another mainly because the vibrational and rotational energy levels in a substance are very closely placed. Because, the electronic energy levels are not so closely spaced, ultraviolet electromagnetic radiation is not transferred with equal felicity, as is also the case with electrical energy.
The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines of different kinds of spectra often used in chemical spectroscopy e.g. IR, microwave, NMR, ESR etc. This is used to identify the composition of remote objects - like stars and far galaxies - by analyzing their radiation (see spectroscopy).
The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or transform other chemical substances.

Chemical laws

Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:


Chemistry 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.
  • 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.
  • Materials chemistry is the preparation, characterization, and understanding of substances with a useful function. The field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry with a focus on fundamental issues that are unique to materials. Primary systems of study include the chemistry of condensed phases (solids, liquids, polymers) and interfaces between different phases.

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.


Further reading

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

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

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

See also


External links

sisterlinks Chemistry
For a full list of external links and suppliers see Wikipedia:Chemical sources.
chemistry in Afrikaans: Chemie
chemistry in Tosk Albanian: Chemie
chemistry in Amharic: የጥንተ፡ንጥር ጥናት (ኬሚስትሪ)
chemistry in Arabic: كيمياء
chemistry in Aragonese: Quimica
chemistry in Franco-Provençal: Ch·imie
chemistry in Assamese: ৰসায়ন
chemistry in Asturian: Química
chemistry in Azerbaijani: Kimya
chemistry in Bengali: রসায়ন
chemistry in Min Nan: Hòa-ha̍k
chemistry in Bashkir: Химия
chemistry in Belarusian: Хімія
chemistry in Bavarian: Chemie
chemistry in Bosnian: Hemija
chemistry in Breton: Kimiezh
chemistry in Bulgarian: Химия
chemistry in Catalan: Química
chemistry in Chuvash: Хими
chemistry in Cebuano: Kemika
chemistry in Czech: Chemie
chemistry in Corsican: Chimica
chemistry in Welsh: Cemeg
chemistry in Danish: Kemi
chemistry in German: Chemie
chemistry in Dhivehi: ކީމިއާއީ އިލްމު
chemistry in Estonian: Keemia
chemistry in Modern Greek (1453-): Χημεία
chemistry in Spanish: Química
chemistry in Esperanto: Kemio
chemistry in Basque: Kimika
chemistry in Persian: شیمی
chemistry in Faroese: Evnafrøði
chemistry in French: Chimie
chemistry in Western Frisian: Skiekunde
chemistry in Friulian: Chimiche
chemistry in Irish: Ceimic
chemistry in Gan Chinese: 化學
chemistry in Manx: Kemmig
chemistry in Scottish Gaelic: Dùileòlachd
chemistry in Galician: Química
chemistry in Gujarati: રસાયણ શાસ્ત્ર
chemistry in Classical Chinese: 化學
chemistry in Hakka Chinese: Fa-ho̍k
chemistry in Korean: 화학
chemistry in Armenian: Քիմիա
chemistry in Hindi: रसायन शास्त्र
chemistry in Croatian: Kemija
chemistry in Ido: Kemio
chemistry in Indonesian: Kimia
chemistry in Interlingua (International Auxiliary Language Association): Chimia
chemistry in Interlingue: Chimie
chemistry in Ossetian: Хими
chemistry in Xhosa: IKhemistri
chemistry in Icelandic: Efnafræði
chemistry in Italian: Chimica
chemistry in Hebrew: כימיה
chemistry in Javanese: Kimia
chemistry in Kannada: ರಸಾಯನಶಾಸ್ತ್ರ
chemistry in Georgian: ქიმია
chemistry in Kashubian: Chemijô
chemistry in Kazakh: Химия
chemistry in Cornish: Kymystry
chemistry in Kirghiz: Химия
chemistry in Swahili (macrolanguage): Kemia
chemistry in Haitian: Chimi
chemistry in Kurdish: Kîmya
chemistry in Ladino: Kemika
chemistry in Lao: ເຄມີສາດ
chemistry in Latin: Chemia
chemistry in Latvian: Ķīmija
chemistry in Luxembourgish: Chimie
chemistry in Lithuanian: Chemija
chemistry in Limburgan: Sjemie
chemistry in Lingala: Kémi
chemistry in Lojban: xumske
chemistry in Lombard: Chímica
chemistry in Hungarian: Kémia
chemistry in Macedonian: Хемија
chemistry in Malayalam: രസതന്ത്രം
chemistry in Maltese: Kimika
chemistry in Maori: Mātauranga matū
chemistry in Malay (macrolanguage): Kimia
chemistry in Min Dong Chinese: Huá-hŏk
chemistry in Mongolian: Хими
chemistry in Dutch: Scheikunde
chemistry in Dutch Low Saxon: Scheikunde
chemistry in Nepali: रसायनशास्त्र
chemistry in Japanese: 化学
chemistry in Pitcairn-Norfolk: Kemistrii
chemistry in Norwegian: Kjemi
chemistry in Norwegian Nynorsk: Kjemi
chemistry in Narom: Chimie
chemistry in Novial: Kemie
chemistry in Occitan (post 1500): Quimia
chemistry in Panjabi: ਰਸਾਇਣ ਵਿਗਿਆਨ
chemistry in Pushto: کيميا
chemistry in Low German: Chemie
chemistry in Polish: Chemia
chemistry in Portuguese: Química
chemistry in Romanian: Chimie
chemistry in Quechua: Chaqllisinchi
chemistry in Russian: Химия
chemistry in Samoan: Kemisi
chemistry in Sanskrit: रसायनशास्त्रं
chemistry in Sardinian: Chìmica
chemistry in Scots: Chemistry
chemistry in Albanian: Kimia
chemistry in Sicilian: Chìmica
chemistry in Simple English: Chemistry
chemistry in Silesian: Chymja
chemistry in Swati: Ikhemisi
chemistry in Slovak: Chémia
chemistry in Slovenian: Kemija
chemistry in Somali: Kimisteri
chemistry in Serbian: Хемија
chemistry in Serbo-Croatian: Kemija
chemistry in Saterfriesisch: Chemie
chemistry in Sundanese: Kimia
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chemistry in Tagalog: Kimika
chemistry in Tamil: வேதியியல்
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chemistry in Thai: เคมี
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chemistry in Tajik: Химия
chemistry in Turkish: Kimya
chemistry in Turkmen: Kimya
chemistry in Ukrainian: Хімія
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chemistry in Venetian: Chìmega
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chemistry in Yiddish: כעמיע
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chemistry in Chinese: 化学

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