(a) Formation of Aluminium Nitride (AlN):
Electronic configuration:
Al loses 3 electrons to form Al³⁺:
$$\text{Al} \rightarrow \text{Al}^{3+} + 3e^-$$
$$2,8,3 \quad\quad 2,8$$
N gains 3 electrons to form N³⁻:
$$\text{N} + 3e^- \rightarrow \text{N}^{3-}$$
$$2,5 \quad\quad\quad 2,8$$
Al³⁺ and N³⁻ attract each other to form AlN.
---
(b) Reason for brittleness of ionic compounds:
Ionic compounds consist of a regular arrangement of oppositely charged ions held together by strong electrostatic forces. When pressure is applied, the layers of ions shift slightly. Ions of the same charge come opposite each other, causing strong repulsion between like charges. This repulsion breaks the crystal apart, making ionic compounds brittle.
Source: Chapter 3, Section 3.3.1
---