Question

Give the electron-domain and molecular geometries of a molecule that has the following electron domains on its central atom: (a) four bonding domains and no nonbonding domains, (b) three bonding domains and two nonbonding domains, (c) five bonding domains and one nonbonding domain, (d) four bonding domains and two nonbonding domains.

Short answer

(a) Electron-domain geometry: tetrahedral; Molecular geometry: tetrahedral. (b) Electron-domain geometry: trigonal bipyramidal; Molecular geometry: T-shaped. (c) Electron-domain geometry: octahedral; Molecular geometry: square pyramidal. (d) Electron-domain geometry: octahedral; Molecular geometry: square planar.

Step-by-step solution

(a) Four bonding domains and no nonbonding domains

In this case, since there are four bonding domains and no nonbonding domains, the electron-domain geometry will be a tetrahedral shape. Since the molecular geometry only accounts for the positions of bonded atoms and all atoms are bonded, the molecular geometry will also be tetrahedral.

(b) Three bonding domains and two nonbonding domains

In this situation, with three bonding domains and two nonbonding domains, the electron-domain geometry is trigonal bipyramidal. For the molecular geometry, we must consider only the positions of the bonded atoms. The nonbonding domains take up equatorial positions, so the molecular geometry will be T-shaped, as there will be three bonded atoms along with a 90-degree bond angle.

(c) Five bonding domains and one nonbonding domain

In this case, five bonding domains and one nonbonding domain add up to a total of six electron domains. Therefore, the electron-domain geometry is octahedral. The molecular geometry must account only for the positions of the bonded atoms. The nonbonding domain will occupy one position, while the bonded atoms will occupy the other five positions, giving the molecular geometry a square pyramidal shape.

(d) Four bonding domains and two nonbonding domains

In this scenario, four bonding domains and two nonbonding domains together make up a total of six electron domains, so the electron-domain geometry will be octahedral, similar to the case of (c). Regarding the molecular geometry of this molecule, the two nonbonding domains will be located on opposite sides of the central atom, while the four bonding domains form a square plane. Consequently, the molecular geometry will be square planar.