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Network solid list (chemistry)
    #9332436 -

Righto.. I know the common covalent network solids such as diamond, quartz, etc

but does anyone know of some of the less commonly known/recognized ones?

On my chemistry exam (approaching quickly.. >.>) our prof told us specifically there will be a question or two regarding less known network solids, but wouldn't say which ones. My researching has yielded

Boron nitride
Silicon carbide
Titania
Alumina
Silicon

any others? Much thanks :laugh:


--------------------
"We cross our bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke, and a presumption that our eyes once watered."
-Tom Stoppard

"He who makes a beast out of himself gets rid of the pain of being a man."
-Samuel Johnson

I will be a cancer upon you, ravaging all that you love and sundering your beliefs. Then, and only then, once you have fallen so far and are but a shell of that which you once were, I will grant you your every dream.
Only to crush them all before your eyes. You doubted my willpower, you abused my generosity, and now you will recognize my cruelty.
-Anonymous

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Re: Network solid list (chemistry) [Re: Dude96]
    #9332444 -

Probably better for the chemistry forum.  This place is more tech and general science oriented.

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Re: Network solid list (chemistry) [Re: DieCommie]
    #9332449 -

Eh, isn't chem forum specifically for chem with relation to psychadelics there?


--------------------
"We cross our bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke, and a presumption that our eyes once watered."
-Tom Stoppard

"He who makes a beast out of himself gets rid of the pain of being a man."
-Samuel Johnson

I will be a cancer upon you, ravaging all that you love and sundering your beliefs. Then, and only then, once you have fallen so far and are but a shell of that which you once were, I will grant you your every dream.
Only to crush them all before your eyes. You doubted my willpower, you abused my generosity, and now you will recognize my cruelty.
-Anonymous

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Re: Network solid list (chemistry) [Re: Dude96]
    #9332600 -

Seems to me that the chem forum is specifically for people who don't know much about chemistry...  :tongue:

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Re: Network solid list (chemistry) [Re: Dude96]
    #9332761 -

Chem is for chem questions- ask what you like.  And like  ChuangTzu states it isn't like its high level discourse, you're question is probably on the advanced side.


Anyways, this seems like a weird question.  "I'll ask you something but won't tell you what you need to know" WTF?  Is this gen chem?

Truthfully I had never heard the term covalent network solids, though I know the concept of course... Kinda weird.. We never had a name for such that I recall in any of my classes, we just described the structure.


Anyways, I would think, hope, that if the question was asked it would concern something of interest or potential interest for popular research or economicly important things- otherwise I don't know how you'd be supposed to know.


As for what they could ask.  I would think they might ask you about carbon allotropes given their importance.  You identified diamond, but graphite would also seem to meet the definition with respect to only the one plane.  Additionally, carbon nanotubes and similar graphite-like structures are other examples since they can form macroscopic structures of one molecule.

You might wanna be prepared to discuss them since they are industrially important and subject to active interest.  Just maybe state that carbon nanotubes get their strength from the very strong sp2 bonds and they form three dimensional structures by taking a graphite sheet and bending it into tubes or whatnot (not saying that's how their made, just stating an analogy).  So that's something.

You might also discuss the difference between quartz or silica structures and glass.  While all are SiO2, I would think glass wouldn't meet the definition of a network solid since it behaves like a fluid and likewise probably has much smaller molecular units than quartz or silica which could presumably be one giant molecule .  So these are obviously important items and you could talk about that.

Other than the carbons and the silica I can't think of much off the top of my head that is widely used or researched, though surely there is a plethora of stuff- I just don't see her picking something obscure, but who knows.


Oh, and be sure and tell us what the question is!

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Re: Network solid list (chemistry) [Re: johnm214]
    #9332792 -

Yea I will, the more I think about it the more annoying it is..

"There's a question on your exam about something that relates to something. "

Thanks? :P

With regards to Graphite I actually would argue, as graphite is the multi-layered composition of multiple Graphene sub-layers is it not? It is made of purely carbon, although due to its structure conducts electricity.

Additionally - yes this is general chemistry.


Also, I'm certain there will be a question where the polarity of a solid tube of some substance is given as well as several other liquid compounds. We will have to order from lowest capillarity to highest based simply on structure and what we can deduce from that...

What i'm wondering is wtf to do if the tube is completely non-polar? Would the meniscus of any polar compounds simply be convex rather than concave due to cohesive forces and a complete lack of adhesive forces?

Or am I missing something? :o

And yea - this is general chemistry. My prof has her masters in physical chemistry i believe, and is working on a second degree in biochemistry..

She's really into this shit >.>


--------------------
"We cross our bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke, and a presumption that our eyes once watered."
-Tom Stoppard

"He who makes a beast out of himself gets rid of the pain of being a man."
-Samuel Johnson

I will be a cancer upon you, ravaging all that you love and sundering your beliefs. Then, and only then, once you have fallen so far and are but a shell of that which you once were, I will grant you your every dream.
Only to crush them all before your eyes. You doubted my willpower, you abused my generosity, and now you will recognize my cruelty.
-Anonymous

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Re: Network solid list (chemistry) [Re: Dude96]
    #9333004 -

Yeah, that seems pretty stupid for gen chem where you probably won't know the structures neccesarily of some of the stuff. 


And you may be right on graphite, but its merely a definitional thing.  If you had a handful of diamonds would you say that they aren't covalent networks just cuz they aren't all one molecule even though substantial portions are?  What if these diamonds are fused together but with cracks that seperate them?  I would think as long as you explain your answer she shouldn't mark you down, but who knows.  Just look at whatever book or note definition she gave and figure out if a covalent solid includes graphite.  Woulld one plane, one sheet of carbon, be large enough to qualify?  Who knows.

Your other question is the shape of a miniscus in a cappilary composed of nopolar substances like polyethylene? 

The question would be, here is a capillary of polyethylene (example nonpolar construction) and liquids of mercury, water, and hexane.  Order from most convex to most concave, right?

The deal with this is since its relative don't worry about the actual shape, since its hard to predict- at least I can't do it without knowing the shape.


The shape of the meniscus is a function of the attraction of the substance to itself versus its attraction to the walls.  So with water, say, you've got a highly polar substance in glass and the water will be concave trying to attract to the walls to spread out electron density and charge.  With hexane, the hexane is pretty inert and doesn't really care to attract to itself and also doesn't care to attract to the walls of the tube either.  However, given that their is some positive interactio to be had via induced partial charges, I would think the miniscus would still be concave but much, much less so than water- essentially flat.  With mercury, the mercury is highly attracted to itself.  While it does feel attraction to the glass, it is less so than its attraction to itself, and thus mercury would for a convex meniscus.


Now mercury might be a bad example cuz you couldn't know to predict that, but you would know with regard to the hexane and water that water has much more of an attraction to the walls than hexane.


So basically if its nonpolar, I would say that with hexane and water that the water would be more attracted to itself than it would be to the nonpolar capillary, and so it would be slightly convex (a guess, I don't know) whereas the hexane would have weak interactions all around and so would have only the slight dispersion-force mediated interactions with the capillary that favor a very, very, slight concave shape.

So you'd say hexane is most concave cuz it has week interactions with itself and weak interactions with the wall, while water is the least concave cuz it has high attraction to itself through hydrogen bonding and weak interaction with the nonpolar capillary and so it "clumps up" in the more energetically favorable convex shape.


Just remember the shape is the function of the attraction fo the substance for itself versus the attraction to the walls of the capilary.


Check that my answers are correct, I just guessed.  For example, I'm not sure water forms a convex meniscus in any given nonpolar capillary, but I would bet it does if it is nonpolar enough.  I don't wanna get this wrong if I'm incorrect- I never needed to really study this stuff in my gen chem course, and I've only worked with glass  while working with capillary type things.

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Re: Network solid list (chemistry) [Re: Dude96]
    #9334548 -

The question is fine here.  As far as I am concerned, it's more of a materials science type question.

When I hear "network solid",  I think polymers.  I recognize the term network solid polymers specifically from mat-sci.  They are very rigid, with a high degree of branching and cross-linkages, and are very high MW.  That's all covalent bonding, too, so it fits the bill.

However, all the ones you alluded to were ceramics.... is that the only scope of your course, or are you just forgetting to consider polymers as a possibility?


--------------------

Edited by Minstrel (11/29/08 10:23 PM)

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Re: Network solid list (chemistry) [Re: Minstrel]
    #9334913 -

Hmm...didn't even think of polymers :o

That likely is it.

Or the prof will be a complete prick and pull some random ass crap just to knock us on our asses =(.


--------------------
"We cross our bridges when we come to them and burn them behind us, with nothing to show for our progress except a memory of the smell of smoke, and a presumption that our eyes once watered."
-Tom Stoppard

"He who makes a beast out of himself gets rid of the pain of being a man."
-Samuel Johnson

I will be a cancer upon you, ravaging all that you love and sundering your beliefs. Then, and only then, once you have fallen so far and are but a shell of that which you once were, I will grant you your every dream.
Only to crush them all before your eyes. You doubted my willpower, you abused my generosity, and now you will recognize my cruelty.
-Anonymous

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Re: Network solid list (chemistry) [Re: Dude96]
    #9338098 -

for gen chem polymers seems pretty advanced.  Maybe if they describe the structure and just say its alkanes or whatnot with long, long, chains and ask how strong they'd be or something.


I just didn't mention them cuz I don't know how they're considered.  I don't really know how long the chains get, but if she asks about them I guess that means she considers them such.


Maybe just be prepared to discuss that carbon-carbon bonds are strong and that the long chains and crosslinks allows strength so the chains can't slide past each other as easily as say a glass of hexane would.

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