Question 9
Aluminium is 2, 8, 3 and forms three bonds in AlCl3. How many electrons end up around the aluminium atom?
The right answer is the one marked above.
Six. Three bonding pairs is six electrons, so the aluminium atom finishes short of an octet. AlCl3 is one of the compounds where the octet rule does not hold.
Eight is what the octet rule would predict, but aluminium only has three valence electrons to work with. Three is the number of bonds, not electrons, and ten is the count around phosphorus in PCl5.