I have an exam coming up and for the life of me, I cannot figure out a few questions that are likely to appear. Anyone can help, I am desperate.

Question 1

In molecular orbital models, does F3 (3 is a subscript) exist?

Question 2

When drawing the lewis dot structure for XECL4- I calculate 37 electrons. DOes this mean it can't be drawn since it is an odd number, or is there a way to draw it?

Question 3

I am trying to find the molecular weight of a diatomic molecule and I am given density in g/mole at STP. What equation and conversions would I use to solve this problem? I convert g/mole to g/liter and use the formula mm=dRT/P but I am not getting even close to the answer the book has.

QUestion 4

How many sigma and pi bonds does F3CCH(N3)CN have?

Question 5

What is the unit of gas constant R in MKS system?

Thank you so much for your help. Normally I would not ask, but I have been working on probs since last wednesday and am going made with these!