[thetomatohead]

Hey there~! We've just recently been learning about Lewis structures, but there's just a few things that I don't quite understand. For example, the Lewis structure for SO₄^2-, the Sulfur which is the central atom has 4 bonds. But normally, doesn't Sulfur only make 2 bonds because it only has 2 unpaired electrons? So how does that work? And how do you calculate the number of lone pairs that are supposed to be on the other atoms attached to the central atom? This is a very confusing subject to me. Some enlightenment on this topic would be greatly appreciated!  

[Donaldson Tan]

if you perceive that the octet rule holds for sulphur, then it should form 2 bonds (2 single or 1 double bond). However, sulphur is in period 3, thus the octet rule does not hold.

In fact, the maximum number of electrons in a given shell is 2n². When n=2, the max number of electron is 8. This is the basis of the octet rule. However, when n=3, the max number of electron is 18.

This means sulphur is capable of accepting electrons to form bonds. You may visualise SO₄^2- as SO₃ accepting an electron pair from O^2-. However, the electrons are free to re-distribute themselves among the S-O bonds.

[thetomatohead]

OHH...Thank you very much.

[Jiro]

http://video.google.com/videoplay?docid=5399558061059901856&q=chemistry%5D

heres a lesson for ya... note i caught him making a mistake for the last resonance structure lol he forgot to check the charge!