Chemistry

Branches of chemistry

; Organic chemistry : Organic chemistry is the science of the structure, properties, composition, and reactions of organic compounds.

; Inorganic chemistry : Inorganic chemistry is the branch of chemistry concerned with 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.

; Physical chemistry : Physical chemistry is the study of the physical basis of chemical systems and processes. Modern chemistry is firmly grounded upon physics, and physical chemistry is the most direct link. Important areas of study include chemical thermodynamics, chemical kinetics, quantum chemistry, statistical mechanics, and spectroscopy.

; Biochemistry : Biochemistry is the study of the chemicals, chemical reactions and chemical interactions that take place in living organisms.

; Analytical chemistry : Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure.

; Minor Branches : Materials science, Polymer chemistry, Environmental chemistry, Pharmacology, Thermochemistry, Nuclear chemistry, Electrochemistry, Computational Chemistry

Fundamental concepts

Nomenclature

Nomenclature refers to the 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.

Atoms

An atom is the smallest irreducible constituent of a chemical system.

Elements

An element is a material that consists of atoms with a given 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 elements is in the periodic table, which groups elements with similar chemical properties together. Lists of the elements by name, by symbol, and by atomic number are also available.

Compounds

A compound is a substance formed from two or more elements, with a fixed ratio determining the composition. For example, water is a compound containing hydrogen and oxygen in the ratio of two to one. Compounds are formed and decomposed by chemical reactions.

Molecules

A molecule is the smallest indivisible portion of a pure compound that retains a set of unique chemical and physical properties. A molecule consists of two or more atoms bonded together.

Bonding

A chemical bond is the force which holds together atoms in molecules or crystals. In many simple compounds, valence bond theory 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 a more thorough understanding based on quantum mechanics is necessary.

States of matter

A phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i.e. density, crystal structure, refractive index, and so forth.) 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.

Reactions

Chemical reactions are transformations in the structure of molecules. Such reactions can result in molecules attaching to each other to form larger molecules, molecules breaking apart to form two or more smaller molecules, or rearrangements of atoms within molecules. Chemical reactions usually involve the making or breaking of chemical bonds.

Quantum theory

Quantum theory describes the behavior of matter at short length scales. It is, in principle, possible to describe all chemical systems using this theory, but it is mathematically complex and profoundly non-intuitive. 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 or Density functional theory). 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.

Laws

The most fundamental concept in chemistry is that the Law of conservation of mass 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. Conservation of energy leads to the important concepts of equilibrium, thermodynamics, and kinetics.

History of chemistry

• Alchemy
• Discovery of the chemical elements
• Timeline of chemical element discovery
• Nobel Prize in chemistry

See also

• List of chemistry topics
• Chemist and List of chemists
• American Chemical Society
• International Union of Pure and Applied Chemistry
• Chemical engineering
• Periodic table
• List of compounds
• List of important publications in chemistry

Links

• on
• IUPAC Nomenclature Home Page, see especially the "Gold Book" containing definitions of standard chemical terms
• Material safety data sheets for a variety of chemicals