Question

how do u draw the lewis structure for something like CO -2 over 3. do u add 2 electrons on to the oxygen when yur finding the number of valence electrons cuz that's wat i thought u did but then i got all those questions wrong so wat do u do

Answer 1

It's very difficult to draw structures on these boards. I'll try to draw and talk you though it for the carbonate ion, CO₃⁼. Yes, you do add two electrons to account for the negative 2 charge on the ion.

1 C with 4 electrons each = 4 e
3 O with 6 electrons each = 18 e
2 electrons for the -2 charge = 2 e
Total number of electrons = 24.

There are four atoms, each wants eight for the octet; and 4 x 8 = 32 electrons. Therefore, we need to make 24 electrons appear to be 32. There are 32 - 24 = 8 and two electrons/bond = 4 bonds. So I start with 4 bonds on C which makes a bond to each O and a double bond to one of the O atoms.

O
|
C=O
|
O
On the top O place pairs of electrons left side, top and right side. On the bottom O place pairs of electrons left side, bottom, and right side. On the side O, place pairs of electrons on top, and bottom (none on the right side). Each dash I drew stands for 2 electrons and you may replace each dash with a pair of electrons. If you have followed my instructions, there should be 8 electrons around the top O, 8 around C, 8 around the bottom O and 8 around the right O. But you should be able to count only 24 electrons. I hope this helps.