Page 1 of 1

acid/base

Posted: Tue Nov 10, 2015 1:06 pm
by chemgal4L
Does the shape of a molecule ever have the ability to determine whether the molecule will act as a lewis acid or base?

Re: acid/base

Posted: Wed Nov 11, 2015 2:52 pm
by Ronald Yang 2F
Well, you can infer from a molecule's shape if it's a lewis base. Usually, an atom, ion, or molecule with a lone pair of electrons can be a Lewis base, since it can donate that electron pair. Thus, if it has a shape like trigonal pyramidal, bent, or other shapes that include lone pairs and follows a AXnEm VSEPR form, with n being number of atoms around the central atom and m being the number of lone pairs, then it can act as a lewis base. To determine if a molecule is a lewis acid, it's difficult to infer from the shape itself; you'd have to look more at the atom that is accepting electron pairs. If the central atom has an incomplete octet (like Boron in BF3) or an expanded octet (like Silicon in SiF4), it probably can act as a lewis acid, as it can accept more electron pairs.