 Let's try trichloromethane, CHCl3, so first valence electrons, carbon has 4, hydrogen has 1 and I have 3 chlorines each of which has 7 which equals 21. When I total those up I've got 21 plus 5 which is 26 valence electrons to play with. Next I look at bonds, carbon which is in group 4 will form 4 bonds, hydrogen we know forms only 1 and chlorine is in group 7 which means it has a valence of minus 1 so it likes to form one bond as well. So each of the chlorines is going to form one bond. Alright so carbon forms 4 bonds and I have four other atoms which each want to form one bond so the skeleton structure is going to have to look like this. That's the only way that I can give carbon 4 bonds and each of the others only one. Okay now I check for the full outer shell. Carbon forms 4 bonds, each bond gives it 2 electrons so it's got 8 so it's fine. Hydrogen has formed one bond which gives it 2 electrons, it's also fine. The chlorines however have only formed one bond which gives them 2 electrons but they need 8. Now if you recall I told you that chlorine was an exception to the rule meaning that it could accept more than 8 electrons. However the default is 8 so you shouldn't try and give the hypervalent atoms more electrons than they need unless it's absolutely necessary. So we're going to go with the default here we're going to say that each chlorine needs 8 electrons and I can't give them any more bonding electrons so we're going to have to do it by non-bonding. So I'm going to give each chlorine 3 pairs of non-bonding electrons. Now each chlorine has 6 non-bonding electrons and 2 bonding electrons which gives it 8 which is a full outer shell. The final step is to check the totals. So I started off with 26 valence electrons so when I count up the electrons in my structure I want there to be 26. So I have 2, 4, 6, 8, 10, 12, 14, 16, 18 non-bonding electrons that's all of the lone pairs, 18 and then 8 electrons from the 4 bonds and 18 plus 8 equals 26. So I have the same number of electrons in the structure as I started with so that's the correct structure for trichloromethane.