Fig. 1: Four electron-pair arrangements around a central atom A, labelled P, Q, R and S. Bonded atoms are written X and each lone pair is drawn as a shaded lobe with two dots. P: a trigonal bipyramid with one axial X above, one axial X below, two equatorial X atoms and one equatorial lone pair. Q: a trigonal bipyramid with X above and below, one equatorial X, and two equatorial lone pairs. R: an octahedron with X atoms at five corners, above and at four corners around the middle, and a lone pair at the bottom corner. S: an octahedron with four X atoms in a square around the middle and two lone pairs, one above and one below.