Chemical reactivity of group 15 elements towards hydrogen, oxygen, halogens, and metals are discussed below.
(i) Reactivity towards hydrogen: Group 15 elements react with H to form hydrides of type EH3 where E=N, P, As, Sb or Bi. On moving down from NH3 to BiH3, the stability of the hydrides decreases. For example, the P-H bond in PH3 is less stable than the N-H bond in NH3. The strength of the E-H bond gets weaker as the size of the central atom increases.
Stability order of E-H bond (where E is group 15 elements) can be represented as
N-H > P-H > As-H > Sb-H > Bi-H
(ii) Reactivity towards oxygen: Group 15 elements react with O to form oxides of the type E2O3 and E2O5 where E = N, P, As, Sb or Bi. The oxide of the element with higher oxidation state is more acidic than those with lower oxidation states. Down the group, the acidic character of the oxides decreases.
(iii) Reactivity towards halogens: Group 15 elements form halides of the type EX3 and EX5 where E = N, P, As, Sb or Bi. However, N does not form pentahalides EX5 as it lacks d-orbital. All group 15 elements form trihalides but trihalides of N are unstable.
(iv) Reactivity towards metals: Group 15 elements react with metals to form compounds of general formula M3E2 where E= N, P, As, Sb or Bi. The binary compounds formed by the reaction of group 15 elements with metal show oxidation state -3.
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