Question

What are the electron-domain and molecular geometries of a molecule that has the following electron domains on its central atom? (a) three bonding domains and no nonbonding domains, (b) three bonding domains and one nonbonding domain, (c) two bonding domains and two nonbonding domains.

Short answer

(a) For three bonding domains and no nonbonding domains, both electron-domain and molecular geometries are trigonal planar. (b) For three bonding domains and one nonbonding domain, the electron-domain geometry is tetrahedral, and the molecular geometry is trigonal pyramidal. (c) For two bonding domains and two nonbonding domains, the electron-domain geometry is tetrahedral, and the molecular geometry is bent or angular.

Step-by-step solution

a) Three Bonding Domains and No Nonbonding Domains

In this case, the central atom has three bonding domains and no nonbonding domains. Based on the VSEPR (Valence Shell Electron Pair Repulsion) theory, when the central atom has three bonding domains, the electron-domain geometry will be trigonal planar, and the molecular geometry will also be trigonal planar, as there are no nonbonding domains. So, for this case, both electron-domain and molecular geometries are trigonal planar.

b) Three Bonding Domains and One Nonbonding Domain

In this case, the central atom has three bonding domains and one nonbonding domain. The presence of the nonbonding domain will slightly distort the geometry. The electron-domain geometry will be tetrahedral, as there are four total domains (three bonding and one nonbonding). The molecular geometry will be trigonal pyramidal, as the nonbonding domain will occupy one vertex of the tetrahedron, leaving the other three for the bonding domains. So, for this case, the electron-domain geometry is tetrahedral and the molecular geometry is trigonal pyramidal.

c) Two Bonding Domains and Two Nonbonding Domains

In this case, the central atom has two bonding domains and two nonbonding domains. Similar to the previous case, the presence of nonbonding domains will distort the geometry. The electron-domain geometry will still be tetrahedral, as there are four total domains (two bonding and two nonbonding). However, the molecular geometry will be bent or angular, as two vertices of the tetrahedron are occupied by nonbonding domains, leaving the other two for the bonding domains. So, for this case, the electron-domain geometry is tetrahedral and the molecular geometry is bent or angular.