Question

Why is `AlF_3` ionic while `AlCl_3` covalent compound?

Answer 1

see below

Explanation:

it depends fron the difference of value of elettronegativity between F (4,0) and Al (1,5) = 2,5 , while with Cl (3.0) and Al you have 1,5 of difference. Generally a bond is told ionic when the difference of elettronegativity is more than 1,7, and covalent when it is less of this value, but the differnce between the two bonds is not so decisive, infact one bond disappears into the other increasing the difference of elettronegativity.

Really `AlCl_3` has a 40% of ionic caracter and 60% of covalent so it can be agevolly used as a catalyst in organic chemistry during aromatic alogenations.