 Okay, third example, boron trifluoride, valence electrons, boron has three and there are three fluorines which are in group seven, so they each have seven. When I total that up I have 24 electrons to play with. For bonds, boron is in group three, it likes to form three bonds. Fluorine is in group seven, it likes to form one bond. So I have three fluorines and one boron, I'm going to put the boron in the middle and use one bond each to join up the fluorines. Now I'm going to check for full outer shells. Boron has access to six electrons. Now remember boron is one of the electron deficient exceptions, so it's happy with six. We don't need to give it any more. The fluorine however, it's one of the ones that really needs a full outer shell and at the moment each fluorine only has access to two bonding electrons. So I'm going to need to give each fluorine three lone pairs so that it now has six non-bonding electrons and two bonding electrons giving it a full outer shell of eight. And then we check our totals. So in my structure here I have two, four, six, eight, ten, twelve, fourteen, sixteen, eighteen non-bonding electrons and then six bonding electrons and eighteen plus six is twenty four, so I have the right number of electrons, so I'm all good.