Reactivity towards hydrogen:
All the elements of group 15 form hydrides of the type EH3.
Here E can be nitrogen, phosphorus, arsenic, antimony or bismuth.
2E + 3H2
N2 + 3H2
+ 6H2 →
+ 6H2 →
4Sb + 6H2 →
4Sb + 6H2 →
The stability of hydrides decreases from ammonia to bismuthine. This is because the central atom E increases in size down the group. With the increase in the size of the central atom, the E – H bond becomes weaker.
With the increase in size, the overlapping between the orbitals of E and hydrogen will not be effective. This accounts for the decrease in the stability of hydrides as we move down the group.
Hydrides of group 15 elements are strong reducing agents. The reducing character of hydrides increases from ammonia to bismuthine due to a decrease in the strength of the E – H bond down the group. Bismuthine is the strongest reducing agent among all the hydrides of group 15 elements.
These hydrides are basic in nature. They act as Lewis bases due to the availability of a lone pair of electrons on the central atom. The basic character decreases down the group with an increase in the size of the central atom.
The boiling point of hydrides decreases from ammonia to phosphine, and then increases from phosphine to bismuthine. The same trend is observed for their melting points.
Reactivity towards oxygen:
Group 15 elements form 2 types of oxides; They are E2
Nitrogen shows a strong tendency to form pπ-pπ bonds with oxygen. Hence nitrogen forms a wide range of oxides. Nitrogen forms 5 stable oxides,
| Oxidation State
Electronic Configuration of Bi: [Xe]4f14
Bismuth can’t form oxides in +5 oxidation state because of the inert pair effect. Oxides in the higher oxidation state of an element are more acidic than that of the lower oxidation state. Hence the acidic strength of oxides of nitrogen increases from N2
As we move down the group, the acidic character decreases. In other words, the basic character of oxides increases on moving down the group.
Reactivity towards halogens:
All the elements of group 15 form trihalides and pentahalides with the general formula EX3
2E + 2X2
2E + 5X2
All the trihalides of these elements, except those of nitrogen, are stable. Phosphorus, arsenic and antimony form pentahalides due to the presence of vacant d orbitals in their valence shells. Nitrogen does not form pentahalides due to the absence of a d orbital in its valence shell. Pentahalides are more covalent than the corresponding trihalides. Moreover, the covalent character of halides decreases from nitrogen to bismuth.
All the elements of group 15 react with metals to form their binary compounds showing -3 oxidation state with the general formula M3
. Here, M stands for metals while E stands for an element of group 15. EX: calcium nitride, calcium phosphide etc.
3M + 2E → M3
3Ca + N2
6Ca + P2
6Zn + 4Sb → 2Zn3
6Mg + 4Bi → 2Mg3