Large central atoms from the third row and beyond in the periodic table (S, P, Cl, Br), may have ten or twelve electrons in their Lewis structure. These electron pair domains (regions) are as far apart as possible when in a trigonal bipyramidal (for five electron pair regions) or octahedral (six electron pair regions) arrangements.
The octahedral and trigonal pyramidal families of shapes for various combinations of bonding and non-bonding electron pair regions are shown. Recall that because shape describes positions of the outer atoms in a molecule, this depends on the number of non-bonding electron pairs at the central atom.
Nonbonding electron pairs occupy more space closer to the central atom than bonding electron pairs. This has the result that in molecules with non-bonding pairs at the central atom have smaller AX bond angles.
The octahedral and trigonal pyramidal families of shapes for various combinations of bonding and non-bonding electron pair regions are shown. Recall that because shape describes positions of the outer atoms in a molecule, this depends on the number of non-bonding electron pairs at the central atom.
| AX6 octahedral  | AX5E square pyramid  | AX4E2 square planar  |
| AX5 trigonal bipyramid  | AX4E see-saw  | AX3E2 t-shaped  | AX2E3 linear  |
Nonbonding electron pairs occupy more space closer to the central atom than bonding electron pairs. This has the result that in molecules with non-bonding pairs at the central atom have smaller AX bond angles.