Chapter 12, Problem 11STP

Solution

Interpretation : The names of the shapes of the molecules for each compound is to be found. The atomic arrangements in each compound result in their different shapes to be explained.

Concept Introduction : The Valence Shell Electron Pair Repulsion model, or VSEPR model, is used to calculate the molecular structure. This model is based on a configuration that reduces the attraction between shared and unshared electron pairs surrounding the main atom.

The shape of the molecules for the compound ${\text{AlCl}}_{\text{3}}$ is trigonal planar and the compound ${\text{PCl}}_{\text{3}}$ is trigonal pyramidal. They have different shapes due to the different numbers of valence electrons in aluminum and phosphorous.

Atomic orbitals combine during the hybridization process to create brand-new, identical hybrid orbitals.

In the compound ${\text{AlCl}}_{\text{3}}$ , the aluminum atom bonds with three chlorine atoms.

There are three valence electrons in aluminum which form bonds with three chlorine atoms. So, there are no valence electrons in the compound.

The shape of the compound is detected with the help of hybridization and VSEPR theory.

There are three bonds, so the hybridization is ${\text{sp}}^{\text{2}}$ and the shape for ${\text{sp}}^{\text{2}}$ hybrid orbitals is trigonal planar.

In the compound ${\text{PCl}}_3$ , the phosphorous atom bonds with three chlorine atoms.

There are five valence electrons in phosphorous where the three electron forms a bond with three chlorine atoms and a lone pair of the electron is left unpaired. So, there is one lone pair of electrons in the compound.

There are three bonds and one lone pair, so the hybridization is ${\text{sp}}^3$ and the shape for ${\text{sp}}^3$ hybrid orbitals with one lone pair is trigonal pyramidal.

Though the compounds have similar formulae, they have different valence electrons.