Читать книгу Foundations of Chemistry - Philippa B. Cranwell - Страница 96

The shape of a covalently bonded molecule or ion is determined by the number and arrangement of the pairs of electrons around the central atom. Electron pairs are negatively charged centres and are repelled by neighbouring centres of electron density. The structures formed are most stable when the centres of electron density are as far apart as possible from each other. If you remember this, you will be able to tackle any problems involving the shapes of simple molecules. The process for working out the shape of a molecule is called valence shell electron pair repulsion theory, or VSEPR for short. It is much simpler than the name suggests!

The arrangement of atoms around a bonding centre is entirely based upon the repulsion of areas of negative charge.

In this model, a single area of electron density or charge is defined as:

 A lone pair of electrons

 A single bond – composed of one pair of electrons

 A double bond – composed of two pairs of electrons

 A triple bond – composed of three pairs of electrons