Lewis Acids and Bases

[Drake_Everlove_1K]

Hi,

So I was wondering; if I have a compound with a central atom like Phosphorous, which can accept an expanded octet, how do I determine if it is a Lewis acid or base? If P has, say, 4 single bonds and a lone pair, would it like to donate that lone pair, making it a Lewis base?

If P has a formal charge of +1 and has 4 single bonds to other atoms, does it want another bond? Is it a Lewis acid by that definition>

[Alex Dib 4H]

Hi, I think this only applies to elements in group 13 because they have 3 valence electrons and don't complete a full octet, but will have 6 instead. An anion or terminal atom of a molecule can donate an electron pair to form a bond with that group 13 element, giving it an octet. The group 13 element that accepts the electron pair/bond is the acid, while the anion or atom that donates is the base.

[Vincent Tse 2B]

A lewis base is any species that donates an e- pair whereas a lewis acid is any species that accepts an e- pair.

You might want to refer to the examples given on pages 85-86 in the course reader as they relate this concept to coordinate covalent bonds.

Hope this helped!

[Mimi_Giang_1F]

Is it that why in BCl3, the B is considered the Lewis acid (accepts 3 electrons from each of the Cl's to complete its shell of 6 electrons)?
I had previously thought that B would be considered the base, donating it's 3 outer electrons to each of the Cl's that only need one more electron to finish their octets.