Question

Select the correct reason for given statement 'Fluoride of $Al$ is ionic while chloride is covalent'.

• A. IE of $Al$ in ${AlF}_3>{AlCl}_3$
• B. EA of $fluorine>chloride$
• C. Lattice energy of ${AlF}_3>{AlCl}_3$
• D. EA of $fluorine<chlorine$

Answer 1

Answer: (A)

IE of $Al$ in ${AlF}_3>{AlCl}_3$

Electronegativity is the reason for that. Electronegativity of Aluminum has a value of around 1.5; fluoride around 4, and chloride around 3.
In aluminium fluoride, the difference between a $F$ and $Al$, in terms of electronegativity, is $2.5$ In aluminium chloride, it is 1. So a bond is covalent is this difference in EN is less than $1.2$, is polar from a difference of $1.2$ to $1.8$, and ionic for a difference of $1.8$ and greater.