CBSE Class 12 Chemistry Notes: The p Block Elements – Nitrogen Family (Halides)

Two types of halides are available for this group. One is MX₃ and another is MX₅ type.

MX₃: NCl₃, PCl₃, AsCl₃, SbCl₃ and BiCl₃
MX₅: PCl₅, AsCl₅, SbCl₅

(a) Tri halides

(i) All trihalides are covalent except BiF₃ which is ionic.

(ii) Like hydrides these trihalides have pyramidal structure and a central atom is sp³ hybridized.

(iii) These trihalides can be easily hydrolyses by water except NX₃.
PCl₃ + 3H₂O → H₃PO₃ + 3HCl
AsCl₃ + H₂O → As₂ O₃ + 6HCl
SbCl₃ + H₂O → SbOCl + 2HCl
BiCl₃ + H₂O → BiOCl + 2HCl

(iv) The trihalides of P, As and Sb acts as Lewis acids and combine with Lewis bases.
PF₃ + F₂ → PF₅
SbF₃ + 2F^– → [SbF₅]^2-

(b) Penta halides
In this central atom attains sp³d hybridization and forms five covalent bonds with five chlorine atoms.

Penta halides have less thermal stability as compared to trihalides. All penta halides act as Lewis acids.

PCl₅ + Cl^– → PCl ₆ ^–
SbCl₃ Cl ^– → [SbCl₄]^–

PCl₅exists as molecule in gaseous state but in solid it exists as [PCl4]⁺ [PCl6]^– and is ionic in nature. PBr₅, PI₅ also exist in the ionic form in solid state.

Illustration 1. Are all the five bonds of PCl5 equivalent? Justify your answer.
Solution: PCl₅ has trigonal bipyramidal structure. It has three equivalent equatorial and two equivalent axial P – Cl bonds. However, due to greater bond pair – bond pair repulsions, the axial P – Cl bonds are longer and hence different from the three equatorial bonds.

Illustration 2. Among the trihalides of nitrogen, which one is the least basic?
(A) NF₃ (B) NCl₃
(C) NBr₃ (D) NI₃
Solution: (A)

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