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Lewis structure for SO4 2-

I’ve watched YouTube videos on it and I don’t get it
I don’t get where the double bonds come from
And why there’s extra electrons that form the double bond
And I saw some videos on formal charge but that wasn’t mentioned in my module
Original post by Blue_skies124
I’ve watched YouTube videos on it and I don’t get it
I don’t get where the double bonds come from
And why there’s extra electrons that form the double bond
And I saw some videos on formal charge but that wasn’t mentioned in my module


The double bonds are caused by 'd' orbitals getting involved in the bonding. It is possible to draw the structure without double bonds, tetrahedral, symmetrical structure (below), but empirical evidence suggests that there is some contribution from pi orbitals (shorter S-O bonds) caused by bringing the 'd' orbitals into play.

SO42-.png
Original post by charco
The double bonds are caused by 'd' orbitals getting involved in the bonding. It is possible to draw the structure without double bonds, tetrahedral, symmetrical structure (below), but empirical evidence suggests that there is some contribution from pi orbitals (shorter S-O bonds) caused by bringing the 'd' orbitals into play.

SO42-.png


Were the D orbitals involved because of promotion
So S has expanded its octet to accommodate the extra electrons

If it was the image you showed, does that mean some electrons between oxygen and sulfur weren’t shared
Original post by Blue_skies124
Were the D orbitals involved because of promotion
So S has expanded its octet to accommodate the extra electrons

If it was the image you showed, does that mean some electrons between oxygen and sulfur weren’t shared

Once the oxygen atoms are bonded via sigma orbitals, there can be interaction between the lone pairs on the oxygen atoms and the empty orbitals on the sulfur giving pi interactions.
Spectroscopic studies suggest that this contributes to the bonding. Hence the bonds are intermediate between S-O single and S=O double. As the structure is an ion, the pi system is delocalised over the whole structure.
Reply 4
If you do formal charge calculations, you will see that the sulfur (S) atom has a charge of +2, while all oxygen atoms have a charge of -1.

Therefore, we need to minimize these charges by moving the electron pair from the oxygen atom to the sulfur atom.

After the displacement of an electron pair from an oxygen atom to a sulfur atom, the charges of sulfur and two oxygen atoms become equal to zero. And this is a more stable Lewis structure for SO4 2-.

There are two -ve charges left on the oxygen atoms, giving a formal charge of -2 on the SO4 molecule.
(edited 8 months ago)

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