Whats wrong with the simple view of PCl3?
This diagram only shows the outer (bonding) electrons. Nothing is wrong with this! (Although it doesn’t account for the shape of the molecule properly.) If you were going to take a more modern look at it, the argument would go like this: Phosphorus has the electronic structure 1s22s22p63s23px13py13pz1. If we look only at the outer electrons as “electrons-in-boxes”: There are 3 unpaired electrons that can be used to form bonds with 3 chlorine atoms. The four 3-level orbitals hybridise to produce 4 equivalent sp3 hybrids just like in carbon – except that one of these hybrid orbitals contains a lone pair of electrons. Each of the 3 chlorines then forms a covalent bond by merging the atomic orbital containing its unpaired electron with one of the phosphorus unpaired electrons to make 3 molecular orbitals. You might wonder whether all this is worth the bother! Probably not! It is worth it with PCl5, though. What’s wrong with the simple view of PCl5? You will remember that the dots-and-cross
