9th of September 2015

1. Why AlCl3 is largely covalent and AlF3 is largely ionic. Explain.

Pavitra Jain - CBSE - Class XI Science

Wednesday, September 09, 2015 at 18:21:PM


Hi Pavitra,

Due to the increase in polarization of X- anion by Al3+ cation from F- to I- or due to the increase of the size of the anions from F- to I-, the covalent character of the trihalides of Al is in the order:

AlF3  <  AlCl3  <  AlBr3  <  AlI3

Thus, the fluorine is more electronegative than chlorine and is able to pull away the electron from aluminium atom.

In other words the fluorine atom's attraction on the electron in aluminium is much greater than chlorine. So with chlorine, Al shares the electrons forming a covalent bond while fluorine attracts the electron toward itself forming F- ion and Al3+ ion and thus it is an electrovalent/ionic bond.

Wednesday, September 09, 2015 at 18:34:PM