A molecule ( /ˈmɒlɪkjuːl/) is an electrically neutral group of two or more atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions.

In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition noble gas atoms are considered molecules despite the fact that they are composed of a single non-bonded atom.

A molecule may consist of atoms of a single chemical element, as with oxygen (O2), or of different elements, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.

Molecules as components of matter are common in organic substances (and therefore biochemistry). They also make up most of the oceans and atmosphere. However, the majority of familiar solid substances on Earth, including most of the minerals that make up the crust, mantle, and core of the Earth, contain many chemical bonds, but are not made of identifiable molecules. Also, no typical molecule can be defined for ionic crystals (salts) and covalent crystals (network solids), although these are often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond, quartz, or sodium chloride). The theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without presence of any definable molecule, but also without any of the regularity of repeating units that characterises crystals.

Read more about Molecule:  Molecular Science, History and Etymology, Molecular Size, Molecular Formula, Molecular Geometry, Molecular Spectroscopy, Theoretical Aspects

Other articles related to "molecule, molecules":

Linear Dichroism - Basic Information
... to measure how much more energy is absorbed in one dimension of the molecule relative to the other, providing information to the experimentalist ... As light interacts with the molecule being investigated, should the molecule start absorbing the light then electron density inside the molecule will ... The LD of an oriented molecule can be calculated using the following equation- For most chemical systems this represents an electric transition polarised across the length of the molecule (i.e ...
Molecule - Theoretical Aspects
... The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the ... The simplest of molecules is the hydrogen molecule-ion, H2+, and the simplest of all the chemical bonds is the one-electron bond ... fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of computational chemistry ...
Coelenterazine - Properties
... The molecule absorbs light in the ultraviolet and visible spectrum, with peak absorption at 435 nm in methanol, giving the molecule a yellow color ... The molecule spontaneously oxidizes in aerobic conditions or in some organic solvents such as dimethylformamide and DMSO and is preferentially stored in ...
... The molecule is most commonly used as in biochemistry and cell biology laboratories as a selective inhibitor of the proteasome ... The molecule is a lactam, or cyclic amide ... A number of syntheses of this molecule have been published and there are no less than 1,300 references to this natural product in the literature ...
Langmuir Adsorption Model - Entropic Considerations
... To find the entropy decrease, we find the entropy of the molecule when in the adsorbed condition Using Stirling's approximation, we have, On the ...

Famous quotes containing the word molecule:

    We can come up with a working definition of life, which is what we did for the Viking mission to Mars. We said we could think in terms of a large molecule made up of carbon compounds that can replicate, or make copies of itself, and metabolize food and energy. So that’s the thought: macrocolecule, metabolism, replication.
    Cyril Ponnamperuma (b. 1923)