For metals like copper(I), how does it have a coordination number of 3 in some compounds like [Cu(P(C6H5)3)3]+. I've learned that these coordination bonds are formed by interacting lone pairs from ligands and empty orbitals on the central metal atom. In this case, copper has a 1+ charge and configuration of [Ar] 4s0 3d10 and I'm just slightly confused on how it would form 3 bonds... Would new bonds just be formed between the lone pair on each phosphorous and the 3 4p orbitals from copper? What happens to the 4s orbital in this case? If there's a method to determine the coordination number of a metal with ligands, could you please expand on that as well or refer me to any sources? Thanks!