Use the idea about electronegativity

Question

1.Explain why the bonding in ALF3 is ionic but the ALCL3 is covalent .

Answer 1

Perhaps at your level of chemistry, you are told that AlCl₃ is covalent, and AlF₃ is ionic, but this isn't really true.  But for the sake of your question, it has to do with the difference is electronegativity.  Al has an EN value of 1.5.  That of F is 4.0 and Cl is 3.  Thus, the difference between Al and F (2.5) is greater than the difference between Al and Cl (1.5) making the Al-F bond MORE ionic than the Al-Cl bond.  However, they both have ionic and covalent character in their bonds.