Question

$AlC{l}_3$ is an electron deficient compound but $Al{F}_3$ is not. This is because:

• A. atomic size of F is smaller than Cl which makes $Al{F}_3$ more covalent
• B. $AlC{l}_3$ is a covalent compound while $Al{F}_3$ is an ionic compound
• C. $AlC{l}_3$ exists as a dimer but $Al{F}_3$ does not
• D. $Al$ in $AlC{l}_3$ is in $s{p}^3$ hybrid state but Al in $Al{F}_3$ is in $s{p}^2$ state

Answer 1

The correct option is B $AlC{l}_3$ is a covalent compound while $Al{F}_3$ is an ionic compound

There is this rule called as Fajan's rule which states that with increasing size of the anion and with decreasing size of the cation ionic character of the compound decreases while the covalent character increases.

Here, since the cation is same in both the compounds, the size of the anion decides the nature of the compound. Size of chlorine being greater than fluorine, $AlC{l}_3$ is covalent while $Al{F}_3$ is ionic.