Explain why bond angle of N${{H}_{3}}$ is greater than that of N${{F}_{3}}$while bond angle of PH, is less than that of P${{F}_{3}}$



Both N${{H}{3}}$ and N${{F}{3}}$ are pyramidal in shape with one lone pair on N. However as F has higher electronegativity than H, the electron pair is attracted more towards F in N${{F}{3}}$, i.e., the bond pairs of electrons are away N or in other words, distance between bond pairs is more. Hence the repulsions between bond pairs in N${{F}{3}}$ is less than in N${{H}{3}}$. Thus the lone pair repels the bond pairs of N${{F}{3}}$more than it does in N${{H}_{3}}$. As a result the bond angles decreases to 102.4° only.