Help with Chem Exam
I'm in Chem 101 and just finished an exam, but there are two questions I disagree with the teacher on, I was wondering if people here could either correct me or heighten my resolve:
The compound PBr2Cl3. Is it polar? The choices were yes, no, not enough information. I said that the geometry was trigonal bipyramidal, and that the more electronegative Cl atoms would form around the equator while the Br occupied the poles, making it non-polar. Is that a correct assumption? She said there was not enough info.
This next one, I am 95% sure she is wrong. It was a lattice energy calculation for MgF2. The information given provided the enthalphy changes for magnesium which went without a hitch, and two for flourine: F + e- = F-, and ½F2 -> F. She said that for the calculation, you had to double the energy of the former, which I agree with. But she then went on to say that you do not double the energy required to split the Flouine gas into Flourine atoms. Isn't that saying that the same amount of energy is required to split half a mole of F2 as is required to split a million moles?
I welcome any comments or help people have, thank you for your time.