Is AlCl3 a lewis acid?

1 Answer
Dec 13, 2015

The simple answer is yes.


By definition, a Lewis acid is an electron pair acceptor. Much of the chemistry of aluminum features the filling of the #p# shell by a pair of electrons that derive from a donor atom (a Lewis base):

#AlCl_3 + Cl^(-) rarr AlCl_4^-#

Here, the tetrachloroaluminate anion is an acid-base pair, an adduct. The negative charge on the adduct formally lies on the aluminum centre, because associated with aluminum there are four valence electrons rather than 3. Of course, here chloride anion has acted as a Lewis base, an electron par donor.

What is the change in molecular structure that this reaction exhibits?