Question

How do you know which orbital is vacant just by looking at a molecule, without having to draw the whole molecular orbital diagram?

Answer 1

You can use the Aufbau principle and Madelung rule. You fill the orbitals in this way 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, (8s, 5g, 6f, 7d, 8p, and 9s). There are diagrams that show this as well to make it easier

Answer 2

That does work out, thank you. But is there a way to figure out which exact orbital is empty? Like carbocations have the Pz orbital empty. How do we know that? Why not Px or Py?

Answer 3

I think that you have to fill them in the correct order due to the lowest energy progressing forward. With that being said when youre doing this the nonbinding orbitals are also filled up in a specific order. Im not too sure on my that answer though

Answer 4

Okey doke, thank you for helping anyway....