Chemical bond
The link that holds atoms together in molecules and crystals, arising from electrons being shared or handed over.
A water molecule is one oxygen atom joined to two hydrogen atoms; a crystal of table salt is sodium joined to chlorine. In 1916 the American chemist Gilbert Lewis proposed that a bond is two atoms each putting forward electrons and sharing them as a pair[1].
Why a pair of electrons should hold atoms together could not be explained until quantum mechanics arrived. In 1927 Walter Heitler and Fritz London showed how a hydrogen molecule forms, from the exchange of two indistinguishable electrons and their pairing with opposite spins[2].
In 1931 Linus Pauling extended the approach to many molecules, explaining for example the directions of carbon's bonds[3]. Besides covalent bonds, in which electrons are shared, there are ionic bonds, in which electrons are handed over and the resulting positive and negative ions attract, and metallic bonds, in which electrons move freely through a metal.
Related terms
- Electron pairTwo electrons grouped together as a pair. When two atoms share an electron pair, a chemical bond forms.
- Exchange interactionAn effect with no classical counterpart, arising because identical electrons cannot be told apart even when they swap places. It underlies the chemical bond and magnetism.
- Binding energyThe energy needed to pull something that is held together apart into its pieces. The larger it is, the more tightly the parts are bound.
Sources
- G. N. Lewis, “The Atom and the Molecule,” J. Am. Chem. Soc. 38, 762–785 (1916).
- W. Heitler, F. London, “Wechselwirkung neutraler Atome und homöopolare Bindung nach der Quantenmechanik,” Z. Phys. 44, 455–472 (1927).
- L. Pauling, “The Nature of the Chemical Bond. Application of Results Obtained from the Quantum Mechanics and from a Theory of Paramagnetic Susceptibility to the Structure of Molecules,” J. Am. Chem. Soc. 53, 1367–1400 (1931).