What an Electron Domain Means in Chemistry

An electron domain is any region of space around the central atom in which there is a high probability of finding electrons. A domain of electrons, two electrons in a nonbonding domain sometimes called a lone pair, two electrons in a single bond domain, four electrons in a double bond domain, six electrons in a triple bond domain tends to repel other domains of electrons. Domains of electrons around a central atom will orient themselves to minimize the electron-electron repulsion between the domains.

The number of atoms that a central atom is attached to plus the number of unshared electron pairs that an atom may have. The atom bonded to the central atom by a single or a double or a triple bond is still counted as one electron domain. The geometry of the molecule can then be predicted on the basis of the repulsion of electron domains and the relative magnitudes of these repulsions.

Bonding electron domain is of three types. Single bond (1 pair, 2 electrons); double bond (2 pairs, 4 electrons); triple bond (3 pairs, 6 electrons). Non-bonding electron domains is the pair of valence electrons not involved in a bond.

For example, take NH3. Here the nitrogen has five valence electrons and these five electrons are placed in four hybrid atomic orbitals. N has attached to it three H atoms by three shared electron pairs and therefore N has one unshared electron pair or non-bonded electron pair left. Thus the central atom nitrogen N has a total of four electron domains that is three bonded pairs and one non-bonded electron pair.