For students taking Chemistry 101 at the University of Victoria in the Fall 2013 term.
The transition metals in group _____ have the highest melting points. 8B,6B,2B, 4B, 3B.I put 8B because it is in the middle of the transition metal series.Quiz #6 says it is 6B.Why is that?
6B means the s-d band is half full, thus maximizing bonding. 8B has some of the antibonding part of the band filled.
Is there more practice 2 midterms that we can access?
You will get another from me early next week, and there is relevant material in the final exams at the end of your lab manual. If you need more problems, try MasteringChemistry or your textbook, there should be plenty of examples.
a couple notes about practice midterm 2in question 1 of the written you need the average bond energy of a C=C bond, which is not on the data sheet. is there a way to calculate this? the answer key states that it is givenquestion 3 and 5 of the written have no answers in the answer key
The data sheets change year to year; students sitting that exam were given the value for C=C.
No answers for 3 & 5; you're right, I will go over these in class.
You said we would go over a practice midterm this week, do you no what day we will be doing this?
Hi Professor, about the practice mid-term today, how do you know that Mercury has the same number of bonding electrons as antibonding?
The s-d band can accommodate 12 electrons (s2, d10). Mercury is s2, d10, so the band is full.
on the master chemistry practice assignment problem 11.11 it asks "to arrange substances Pb, Ni, and S in order of increasing boiling point". I thought that because Pb has a higher weight than Ni, it would then have a higher boiling point... but the answer says "S, Pb, Ni".Why is that?
also for question 11.12... I dont understand why Ga has a higher boiling point than Br2
The Pb vs. Ni question is a tough one; you don't know enough about the s-d band vs. the p band to answer this question properly (so don't worry about it). On the other hand, Ga is a metal whereas Br2 is a molecular solid held together by dispersion forces only, so it is reasonable to assume Ga has the higher m.p.
Liquid crystals are confusing to me.How exactly would you determine if a molecule will be a liquid crystal? And will we only need to know smectic,nematic, and cholesteric? Or do we also need to know smectic A and smectic C?
Liquid crystals are rodlike in shape and polar. You don't need to know the difference between smectic A and C
I'm still confused about the question from mastering chem about which group would have the highest melting point, 8B or 6B (the first post). In my notes I've written that metals in the middle of the transition metal series will have half filled bands, but is it actually group 6 because group 1 and 2 are included (i.e. not just transition metals)?
Hi Dr. McIndoe; one of the practice questions on mastering chem asks to arrange Kr, Cu, and HF in order of increasing BP; the answer says Kr is the weakest and Cu is the strongest. I'm not sure I understand why HF wouldn't be the strongest, having a hydrogen bond. Also, in general, do the noble gases have weak intermolecular attractions..?
Re: group 6 vs. group 8; yes, the s-d band is made up of the s and d bands, which overlap almost completely (s and d being of very similar energy in transition metals). So the band can accommodate 12 electrons in total.Re: bp; this q is all about relative strengths of intermolecular forces. Metallic bonding (Cu) is stronger than hydrogen bonding (HF) which is stronger than London dispersion forces (Kr). The strength of metallic bonding varies a lot, but you can ballpark it as about the same as ionic bonding. Yes, noble gases have weak intermolecular forces - they have only dispersion forces and are spherical hence have a low surface area, too.
When drawing the molecular shape, do we draw the lone pairs in or do we only draw the actual atoms in the molecule and the shape the lone pairs pushes the atoms into but not the lone pairs?
Arrange substances Mg , Os , and SO_2 in order of increasing boiling point.Why is Os>Mg ? Is it due to its weight...do we consider bond theory for transition metals?Thanks!
Mg has a full s band, though it still behaves as a metal due to overlap with the p band. Os has a 2/3 filled s-d band, and so still exhibits very strong metallic bonding. You won't get questions like this one, though, because it requires you to know more than you've been taught about bands.SO2 of course just has weak dipole-dipole and dispersion forces to hold it together.
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