Chapter 3, Problem 3.32P

Interpretation Introduction

(a)

Interpretation:

The electron geometries of all nonhydrogen atoms in the four listed species are to be determined.

Concept introduction:

Electron geometry around an atom is determined on the basis of the Valence Shell Electron Pair Repulsion (VSEPR) Theory. Electron geometry describes the orientation of the electron groups in an atom’s valence shell. An electron group is a lone pair or a bond between the two atoms. The bond, whether a single, double or triple, counts as just one electron group.

Since all electrons have the same charge, the electron groups repel each other. They try to move (orient themselves) as far away from each other as possible in order to minimize these repulsions. This results in a linear geometry (${\text{180}}^{\text{o}}$ angle) when there are only two electron groups. Three electron groups are oriented at an angle of ${\text{120}}^{\text{o}}$, resulting in a trigonal planar arrangement. Four electron groups are arranged in a tetrahedral geometry, at $\text{109}{\text{.5}}^{\text{o}}$ angle.

The number of electron groups and geometry is determined on the basis of the Lewis structure of the molecule/ion.

Interpretation Introduction

(b)

Interpretation:

The hybridization of all nonhydrogen atoms in the given four species is to be determined.

Concept introduction:

The concept of hybridization of atomic orbitals is used in Valence Bond (VB) Theory to account for the electron and molecular geometry around an atom. A hybrid orbital is a combination of one or more atomic orbitals from the valence shell of an atom. It typically involves an s orbital and a number of p orbitals from the valence shell, resulting in the same total number of hybrid orbitals of the same energy and shape. In heavy atoms, those from Group 3 onward, the valence shell d orbital may also be involved if the atom has an expanded octet. The orientation of these orbitals is same as the electron geometry of the atom. The number of hybrid orbitals required is the same as the number of electron groups. If the number of electron groups is two, two hybrid orbitals are needed. These are formed by a combination of the s and one p orbital, giving $\text{sp}$ hybridization. For three electron groups, three hybrid orbitals are required, the s and two of the p orbitals, giving ${\text{sp}}^2$ hybridization. Four groups require four orbitals, giving ${\text{sp}}^{\text{3}}$ hybridization.