AlCl3 is lewis acid. Explain how?

Question

stephstar101 · Answer

Lewis acids are substances that can accept electron pairs. Since AlCl3 has 6 electrons, it'll want 2 more (not give 6 away because that's harder to do). Since it wants 2 electrons, it is considered a Lewis acid.

ujjwal · Answer

I didn't get it. AlCl3 has 6 electrons?? And why would a stable compound need electrons?

ujjwal · Answer

@stephstar101

stephstar101 · Answer

Hmmm, you're right, it is stable. I've been mistaken, but I'll look for the answer for you :) Just disregard the previous

ujjwal · Answer

Ok

ujjwal · Answer

I have one more question: 

The total volume of gaseous products obtained at STP by passing two ampere current for 20 min through brine solution is:

stephstar101 · Answer

So apparently AlCl3 has the ability to become AlCl4- which is why it's still a "proton accepter" and therefore a lewis acid. It's just one of those funky weird substances that can have more or less electrons than what is considered "stable." I don't know the second question, however. I'm sorry :(

anonymous · Answer

The Al atom is very small, because it lies on the right-hand side of the table, where effective nuclear charge is high.  That means valence electrons shared with it come rather close to the Al nucleus, which means they are rather strongly attracted.  That's fundamentally what makes Al a Lewis acid: it's electron-hungry.

Three Cl's will partially satisfy it: now it has 6 electrons in the valence shell.  But the valence shell can accomodate 8 electrons, so AlCl3 is still electron-hungry -- a Lewis acid.  Only when you reach AlCl4- do you fill the valence shell.