Lone Pairs Count in 3D Structure Determination

When both bonds and lone pairs surround a central atom, the lone pairs repel one another as well as repel the bond pairs. Thus, when we predict the 3D stmcture of 

SCHEME 7.3 Cases with five and six electron pairs around a central atom. In both cases, the molecules are first constructed using the click method. Then, one counts the electron pairs around the central atoms, and one proceeds to predict the 3D structures (a) With five pairs, PCI5 has a trigonal bipyramidal shape, (b) With six pairs, SFg has an octahedral shape. The red lines in (a) and (b) are not bonds, but rather lines that serve to outline the corresponding polyhedral shapes. 

To appreciate the role of the lone pairs, we could consider the situation if the lone pairs were not geometry-determining. Thus, discounting the lone pair for NH3, we 

Pyramidal shape derived from a tetrahedral geometry 

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