Question

Discuss the trends in chemical reactivity of group 15 elements.

Answer 1

Trends in chemical reactivity of group 15 elements.

1. Reactivity towards hydrogen These elements form covalent hydrides with the formula EH_3. [where, E=N,P,As,Sb]

(a) Thermal stability of hydrides decreases down the group.

(b) Reducing character of hydrides increases down the group.

(c) Basic character of hydrides decreases down the group.

(d) Boiling point of $N{H}_3$ is greater than $P{H}_3$ due to H-bonding. The boiling point of other hydrides increases from $P{H}_3$ onwards.

Lighter elements like nitrogen also form hydrides of the formula $E_2{H}_4.e.g.,N_2{H}_4$

2. Reactivity towards halogens All group 15 elements i.e., N,P, As, Sb, Bi form

(a) Halides of general formula $E{X}_3$. Except for $NB{r}_3$ and $N{I}_3$, all are stable with a pyramidal shape, These get hydrolyzed by water.

(b) Halides of general formula $E{X}_5$.

These are formed by P, As and Sb but not by N. These halides are trigonal bipyramidal with $s{p}^{3}d$ hybridization.

3. Reactivity towards oxygen. These elements form oxides of the formula $E_2{O}_3$ and $E_2{O}_5$.However, nitrogen because of its tendency to form $p\pi -p\pi$ multiple bonds, form a range of oxides having oxidation states +1 to +5 $(e.g.,N_{2}O,NO,N_2{O}_3,N{O}_2,N_2{O}_4,N_2{O}_5)$ $E_2{O}_5$ are more acidic than $E_2{O}_3$. Acidic character of oxides decreases down the group.

4. Reactivity towards metals: The group 15 elements react with metals to form binary compounds in which metals exhibit -3 oxidation states.