JEE Main · 2012 · 29 Apr 2012 · Offline · Chemical Bonding and Molecular Structure

All four trihalides are pyramidal with one lone pair on the central atom, and down the nitrogen group from $\mathrm{N}$ through $\mathrm{P}$ and $\mathrm{As}$ to $\mathrm{Sb}$ the central atom grows larger and less electronegative. As the bonding pairs sit on a bigger, less tightly holding atom, they spread apart less and the lone pair presses them closer, so the bond angle falls steadily down the group. The largest central atom here, antimony, gives $\mathrm{SbC}{\mathrm{l}}_3$ the smallest bond angle.