Molecule

A molecule is an electrically neutral group o twa or mair atoms held thegither bi chemical bonds. Molecules are distinguished frae ions bi thair lack o electrical chairge. Houever, in quantum physics, organic chemistry, an biochemistry, the term molecule is eften uised less strictly, bein applee'd tae polyatomic ions an aa.

In the kinetic theory o gases, the term molecule is eften uised for ony gaseous pairticle regairdless o its composeetion. Accordin tae this defineetion, noble gas atoms are conseedert molecules as thay are in fact monoatomic molecules.

A molecule mey be homonuclear, that is, it conseests o atoms o ane chemical element, as wi oxygen (O₂); or it mey be heteronuclear, a chemical compoond componed o mair nor ane element, as wi watter (H₂O). Atoms an complexes connectit bi non-covalent interactions, sic as hydrogen bonds or ionic bonds, are generally nae conseedert single molecules.

Molecules as components o matter are common in organic substances (an tharefore biochemistry). Thay mak up maist o the oceans an atmosphere. Houever, the majority o fameeliar solit substances on Yird, includin maist o the minerals that mak up the crust, mantle, an core o the Yird, conteen mony chemical bonds, but are nae made o identifiable molecules. Forby, na teepical molecule can be defined for ionic creestals (sauts) an covalent creestals (network solits), awtho thir are eften componed o repeatin unit cells that extend aither in a plane (sic as in graphene) or three-dimensionally (sic as in diamond, quartz, or sodium chloride). The theme o repeated unit-cellular-structur forby holds for maist condensed phases wi metallic bondin, which means that solit metals are nae made o molecules. In glesses (solits that exeest in a vitreous disordered state), atoms mey forby be held thegither bi chemical bonds wi na presence o ony definable molecule, nor ony o the regularity o repeatin units that chairacterises creestals.