I've got an exam tomorrow in periodicity and solid state chemistry. As it stands, I'm gonna be lucky to pass (spent to much time panicking about earlier exams..and the one I've got on friday so haven't done much for this one!). In an attempt to learn something, I'm going to consult the stw masses!

1st question… Anyone know anything about drawing unit cells in crystal structures?
2nd question…whats a band structure? (and a fermi level come to think of it)
and finally

In the gaseous phase, the four trihalides, AlBr3, BBr3, PCl3 and ClF3 have significantly different structures. Describe and rationalise the differences between the structures of the three compounds in terms of the different bonding arrangements within them.

(and there's a similar question with tetrafluorides on another paper.
What are their structures? and why are they different?

I think I'm missing something "simple" on that last one, but my mind is not in a fit state for logic at the moment!

If anyone can help me with any of the above…or knows a good website…it would be much appreciated!

My guess is that the structures move from purely ionic to more of a covalent nature as the electonegativity changes

I know for a fact that there are several chemistry lecturers on here, they may help you out. I suspect that you might be doing it again in august though.

I must add its 15 years since I did my degree.

Go the the library and get

Ashcroft and Mermin, Solid State Physics.

Read chapter 4 and probably 13-15

The last one is a Valence Shell Electron Pair Repulsion (VSEPR) question – generally OK to understand and is in all the text books. You need to work out how many electon pairs each central atom has, you then use simple rules to work out structure.

Have a look here at some examples:

http://winter.group.shef.ac.uk/vsepr/

Band structures depend on a number of things. Are you looking at low-dimensional solids (e.g. BEDT-TTF or the Bechgaard salts?). A fermi surface is the uppermost filling of a band that has free moment of electrons (in a metal, natch), the 'level' bit is the filling. They can be plotted in omega-space (cm-1) which can be very pretty.

BTW a good book on band structures is 'Solids and Surfaces: A Chemist's View of Bonding in Extended Structures' by Roald Hoffman, VCH publishers, ISN 0-89573-709-4

Though it is a bit older these days. It does have areas on band folding and Peierls Distortion.

Ooo, VSEPR, I think I can do that, I was trying to overcomplicate it!
Thanks for the book recomendation, I'll pop to the library on my way back from the dentist ( 🙁 )

Why didn't I pick an easier subject…

I must add its 15 years since I did my degree.

It's only 10 years since I did mine but I haven't looked at phys chem since then…

unit cells are here wikipedia is your friend

What do you need to know about unit cells? If it is just drawing a the generic unit cells, there's not much you can do other than to remember the 14 Bravais lattices.

Here

Edit – Denied

dude, you snooze you lose

Cram like a bugger!

What yr are you in? please don't say final year. If so don't reply and cram!

First year, so its not the end of the world if I fail…
Back from the dentist so back to revision >=].
Thanks guys!

Ah – one of the uni lecturers turned up. 😀

Sounds like A-level chemistry to me….

God I must be old.

A-level?

We were doing Mesons, Baryons, and Leptons for our 11+

It's not how it used to be…..

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(I know it's Physics but I know bugger all about chemistry)

All that looks familiar but I haven't got a clue about it anymore. Twas only 5 years ago. I don't do chemistry anymore, just mixing stuff together and see what happens.

My advice would be that you are up the preverbial creek without a paddle as that sort of stuff is fundamental. Tactical revision/swatting may help rather than trying to understand everything. Find out if certain questions keep coming up and work out how to answer those (like the structures one). Pick areas to know well rather than knowing a little bit about everything.

I'm sooooooooooo glad I didn't folow up my degree with a career in chemistry, engineering is so much easier to get my head arround.

Having been out of uni for 2 years I'm actualy interested enough in my degree subject again to want to read my old test books again!

Well aim to get to get idea right as its only 40% to pass and resit in summer at worst.

Thing is make sure you know it should you need a resit and before yr2 as it will contribute to understanding.

Chemistry is easy but cramming from no revision is just high pressure but it can be done 😉

Good luck with it and don't make the same mistake again! cough

It's first year, therefore it doesn't matter.

Considerably less stressed now I'm back from the dentist!
Some tactical cramming is in order..although 40% can't be that hard…can it?

@thisisnotaspoon its taken less than a year of this degree to put me off working in chemistry!

Its over, it was hard! Might have just scraped 40%. But they've changed the layout from previous years so even one of my best friends who has been revising for weeks and was super ready came out almost in tears 🙁 .

Next exam…half 4 tomorrow…revision done. half an hour. and i've got to get a filling tomorrow lunchtime. fun times.

Good luck with it all. You'll be fine.

😀

Things haven't changed much from my day then. 'What, an exam at the end of the term? bugger!'. Good luck.

I hated all that phys chem stuff. Give me mechanistic organic chem anyday.

Figured I'd update you…got 66 and 61 on those 2 exams. Did well enough overall to get a first for the year (not that it counts but hey!)

wooohooo go you!

Thus proving that the ST forum is the fount of all knowledge…

Wel done 🙂

Well I was going to reply to you. Well done about your degree 😀