Question

The H-N-H angle value is higher than H-P-H, H-As-H and H-Sb-H angles. Why?

Answer 1

Hint: Think about the electronegativity concept. Think what happens to the size of the elements when we move from top to bottom in the same group. Compare the electronic configuration of nitrogen and phosphorus.

Complete step by step answer:
- Electronegativity is the potential of an element to gain electrons in order to complete its octet and attain stability.
-Nitrogen, ${}^{7}N$ is the most electronegative element in the Nitrogen family in the periodic table because it needs only three electrons to complete its 2p-orbital or L-shell. Moreover, due to presence of only two shells, there is negligible shielding effect and so nucleus has the tendency to attract more electrons thereby, making nitrogen the most electronegative element in its group.
-In case of Phosphorous ${}^{15}P$, three electrons are required to complete 3p-orbital to attain noble gas configuration but it can still accept electrons due to vacant 3d-orbitals. So, relatively its electronegativity is low. Also, due to addition of one more shell that is, M-shell, there is some amount of shielding effect which reduces the tendency to attract electrons to some extent thereby, reducing its electronegativity than nitrogen.
-Also, we know that, as the atomic size increases, electron density on the central atom decreases which reduces bond size. If the electron density on the central atom is more, then there will be electron pair repulsions within the molecule which will increase the bond angles.
Therefore, it is justified that the H-N-H angle value is higher than H-P-H, H-As-H and H-Sb-H bond angles.

Note: Remember as the number of shells increases, atomic size increases and the electron density decreases. This is because when there are less number of shells, electrons are added in the same shell.