14. Reactivity towards hydrogen: All group 15 elements from trihydrides, MH3. Hybridisation- sp 3
The stability of hydrides decrease down the group due to decrease in bond dissociation energy down the group.
NH3 > PH3 > AsH3 > SbH3 > BiH3
Boiling point: PH3 < AsH3 < NH3 < SbH3 < BiH3
Boiling point increases with increase in size due to increase in van der Waals forces. Boiling point of NH3 is more because of hydrogen bonding.
Bond angle: NH3( 107.8 °) > PH3( 99.5 °) > AsH3( 91.8 °) ≈ SbH3( 91.3 °) > BiH3( 90 °)
Electronegativity of N is highest. Therefore, the lone pairs will be towards nitrogen and hence more repulsion between bond pairs. Therefore bond angle is the highest. After nitrogen, the electronegativity decreases down the group.
Basicity decreases as NH3 > PH3 > AsH3 > SbH3 < BiH3.
This is because the lone pair of electrons are concentrated more on nitrogen and hence the basicity will be maximum in the case of
NH3. It will decrease down the group as the electronegativity decreases down the group.
The reducing power of hydrides increases down the group due to decrease in bond dissociation energy down the group.
15. Reactivity towards oxygen: All group 15 elements from trioxides( M2O3) and pentoxides( M2O5).
Acidic character of oxides decreases and basicity increases down the group. This is because the size of nitrogen is very small. It has a strong positive field in a very small area. Therefore, it attracts the electrons of water’ s O-H bond to itself and release H + ions easily. As we move down the group, the atomic size increases. Hence, the acidic character of oxides decreases and basicity increases as we move down the group.