Phosphorus(III) chloride molecules are pyramidal with a bond angle less than 109.5°. Explain why a phosphorus(III) chloride molecule has this shape and bond angle.

Phosphorous (III) Chloride consists of one phosphorous atom covalently linked to 3 individual chlorine atoms. Phosphorous is found in group 5 of the periodic table, hence it has 5 outer shell electrons, in which 3 of these participate in covalent bonds with the 3 chlorine atoms. The other 2 electrons are a lone pair of electrons. PCl3 has a pyramidal shape due to electrons on phosphorous arranged for minimal repulsion/maximal separation hence reducing the repulsion between them. Due to the presence of the lone pair the bond angle is further reduced to 107, as lone pair-bond pair repulsions are stronger than those of bond pair-bond pair repulsions.