What is domain in chemistry

In VSEPR theory, an electron domain is a region of electron density around a central atom. A single bond, double bond, triple bond, or lone pair each counts as one domain for the basic geometry analysis.

Meaning and context

Count the domains around the chosen central atom rather than counting every bonding electron separately. A multiple bond contains more than one electron pair, but it occupies one direction or region in this model.

Examples and usage

Carbon in CO₂ has two bonding domains and no lone pairs, giving a linear electron-domain arrangement. Nitrogen in NH₃ has three bonding domains and one lone pair, for four total domains. Its molecular shape differs from its electron-domain geometry.

What to check

The phrase domain has other uses in chemistry and science, so specify electron domain when that is intended. VSEPR predicts useful shapes for many molecules, but it is a model with limits rather than a complete account of all bonding.

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