So we have BF three. Plus an ace that has a lone pair of electrons forms a cordon covalent bond, HBF three. And it's called Cortis covalent and not Covalent because both electrons come from a single atom. Remember, in a Covalent bond, one electron comes from here, and one electron comes from here. But in this case, both electrons come from a single atom. So let's look at the structural depiction of BF three.