The p-Block Elements.

 Hydrides: All elements of group 15 form gaseous hydrides of the type MH₃.
In all the hydrides the central atom is sp³ hybridized and their shape is pyramidal due to presence of lone pair of electrons.
(a)The basic strength of the hydrides decreases as we move down the group.
Thus, NH₃ is the strongest base.
NH₃ > PH₃ > AsH₃ > SbH₃
(b)The thermal stability of the hydrides decreases as the atomic size increases, i.e., the M – H bond strength decreases which means reducing character increases.
(c)In the liquid state, the molecules of NH₃are associated due to hydrogen bonding. The molecules of other hydrides are not associated.
(d)NH₃ is soluble in water whereas other hydrides are insoluble.
(e)All the hydrides, except NH₃, are strong reducing agents and react with metal ions (Ag⁺, Cu²⁺, etc.) to form phosphides, arsenides or antimonides.
Halides: The elements of group 15 form two series of halides MX₃ and MX₅.
(a)All the elements of the group form trihalides. The ionic character of trihalides increases as we move down the group. Except NCl₃ all the trihalides are hydrolysed by water. This is due to the absence of d-orbitals in nitrogen.
(b)PF₃ is not hydrolysed because fluorine being more electronegative than oxygen forms more stable bonds with phosphorus than P – O bonds.
(c)N cannot form NX₅ because of non-availability of rforbitals. Bi cannot form BiX₃ because of reluctance of 6s electrons of Bi to participate in bond formation.
(d)The hybridisation of M in MX₃ is sp³ and shape is pyramidal. M in MX₅ is sp³ as hybridised and shape is trigonal pyramidal. The axial bonds in MX₅ are weaker and longer, So MX₅ are less stable and decompose on heating eg:

Oxides:
(a)Nitrogen forms a number of oxides. The rest of the members (P, As, Sb and Bi) of the group form two types of oxides : E₂0₃ and E₂O₅.
(b)The reluctance of P, As, Sb and Bi to enter into pπ -pπ multiple bonding leads to cage structures of their oxides and they exist as dimers, E₄O₆ and E₅O₁₀.
(c)The basic nature of die oxides increases with increase in atomic number of the element. Thus, the oxides of nitrogen (except N₂0 and NO), P (III) and As (III) are acidic, Sb (III) oxide is amphoteric and Bi (III) oxide is basic.