4.7-4.10 in organic textbook

[Skolli20]

Hi I was just wondering why we are practicing drawing lewis structures? Is there something conceptually new other than the fact that they are nucleophiles we should understand or is it just as a review?

Also for 4.8, the lewis structure for thiosulfate, I thought that there would be a double bond to the O's and not the sulfur because sulfur is bigger so it can stabilize the negative formal charge easier than oxygen? I understand that double bonding it to the oxygens vs an oxygen and a sulfur is just resonance but if someone could clarify?

Also for 4.10, the lewis structure for Azide, I am unclear on why nitrogen can make four bonds because normally it can only make three. How do we know that its two double bonds and not a triple bond and a single bond? Is it due to formal charges?

Thanks and sorry the multiple questions!

[Chem_Mod]

Hi I was just wondering why we are practicing drawing lewis structures? Is there something conceptually new other than the fact that they are nucleophiles we should understand or is it just as a review?

Also for 4.8, the lewis structure for thiosulfate, I thought that there would be a double bond to the O's and not the sulfur because sulfur is bigger so it can stabilize the negative formal charge easier than oxygen? I understand that double bonding it to the oxygens vs an oxygen and a sulfur is just resonance but if someone could clarify?

Also for 4.10, the lewis structure for Azide, I am unclear on why nitrogen can make four bonds because normally it can only make three. How do we know that its two double bonds and not a triple bond and a single bond? Is it due to formal charges?

Thanks and sorry the multiple questions!

The lewis structure exercise is done to give you a sense of where the actual nucleophilic center is, that is, where the electrons are actually coming from.
For thiosulfate there is resonance so the double bond can be either on the oxygen on sulfur at any time.
For azide, there is also resonance so your structure would also be accurate if one accounts for formal charges.