Steric number 5

The general shape adopted by five groups is the trigonal bipyramid, like with  PF₅. There are now two in equivalent types of position, two axial (top and bottom in Fig. 1) and three equatorial. It shows that the equatorial positions allow more space than axial ones. So bulkier groups (e.g. Cl in PF₄Cl) tend to be found in these positions, as do nonbonding  pairs when these are present. With consecutively one, two and three nonbonding pairs, molecular shapes are as follows.

1. AX₄ is frequently explained as a 'see-saw' with two axial and two equatorial X positions, the former being little bent out of the ideal linear configuration by the lone-pair repulsion. Examples are SF₄ (3) and XeO₂F₂ (where O in preference to F occupies the equatorial position; see the rule no. iii).
2. AX₃ gives a T-shape, like in ClF3 (4).
3. AX₂ is linear like the bonded atoms are axial. instances are XeF₂ (5) and