CHAPTER 3 - The Geometry of Molecules of Second Row Atoms

Abstract

This chapter discusses the geometry of molecules of second row atoms. No book on molecular geometry would be complete without the molecules made by bonding second row atoms to one another and to hydrogen. However, the converse of this is that the subject matter has been well traversed. The second row atoms have four valence orbitals, namely, 2s, 2px, 2py, and 2pz, containing up to eight valence electrons. To make bonds between atoms, some redistribution of the atomic electron density is required. At its extremes, two different types of bonding can be identified: (1) covalent and (2) ionic. A pure covalent bond involves equal sharing of the valence electrons, as is the case for homonuclear diatomics such as F2. Different atoms in a molecule will have different abilities to attract and hold onto electrons and therefore, most bonds will have some ionic and some covalent character. The concept of electronegativity is a useful label to use in this context. It describes the ability of an atom to attract electrons to itself and the difficulty with which electrons are removed from it.