Question

The properties of most of the ionic solids deviate from their ideal ionic character because the lattice undergoes some distortion. Cations are usually smaller than anions and have a higher effective nuclear charge. The outer electron cloud in a cation is more firmly held than in an anion. The loose electron cloud of an anion, when attracted by the electron cloud of a cation, gets distorted. This phenomenon is known as polarization. Due to this phenomenon, the electron cloud of an anion shifts towards the cation which decreases both the magnitude of positive charge on the cation and the negative charge on the anion. In other words, covalent character develops in the ionic bond.

Which of the following is an ionic compound?

• A. $Al{F}_3$
• B. $AlC{l}_3$
• C. $AlB{r}_3$
• D. $Al{I}_3$

Answer 1

The correct option is A $Al{F}_3$

In all the given compounds, $Al$ is the central atom while the side atoms are different. According to Fajan's rule, larger the anion more is the covalent character of the compound. Thus, $Al{F}_3$ having the smallest anion among the given, will have less covalent character and thus, it will be an ionic compound.