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 .