Allatropes

[BigMoosie]

It seems to me that ice and water and water vapour should all be classified as different allaltropes of h20. What is it that they are not?

[YT2095]

they are called Phases. Ice can have something similar to different allotropes though, depending on how it was formed, they`re named (rather unimaginatively) Ice(1), Ice(2) etc...

 

here, I dug this up, you may find it interesting

http://www.cmmp.ucl.ac.uk/people/finney/soi.html

[BigMoosie]

Thanksalot YT! Though I don't think that really answers my question. I was thinking, since it takes energy to change any substance's state from solid to liquid, you are changing the bonds at the same time and the physical properties. How is that different from changing graphite into daimond?

[jdurg]

An allotrope is when you have the same ELEMENT but with a different physical structure to it. As soon as you move onto more complex structures involving different elements in a molecule, the term 'allotrope' no longer applies. Instead you get 'isomers' or 'phases'. (Phases is if the structure is the same but the angles and whatnot are different. Isomers are when the formula is the same, but the structure is vastly different).

 

When H2O changes from ice to water, you are NOT changing ANY of the bonds involved. The only things that are changing are the intermolecular bonding of the molecules, not the intramolecular bonding. With ice, there is a rigid structure to the hydrogen bonding since the individual water molecules don't have enough energy to break free. As the temperature increases, the molecules are able to break free and slide past each other which gives us the form known as water. With graphite and diamond, the intramolecular bonding is vastly different. When you go from graphite to diamond, you have to break the chemical bonds between each of the carbon atoms. This is much different than just breaking the intermolecular attractions between them.

 

A good analogy would be if you have two people holding hands. When you go from ice to water, it's like putting a broomstick between their hands and making them break apart. You're not really changing the physical structure of the combination, you're just separating them. Now changing graphite to diamond would be like taking a laser beam and cutting off their arms and then rearranging the severed appendages. In this case, you're making severe changes to the physical structure of the pair.

[LucidDreamer]

The definition of an allotrope: differerent forms of the same element in the same state. Ice and water are in different states, one is a solid and the other is a liquid. Graphite and diamonds are both solids.

[BigMoosie]

When H2O changes from ice to water, you are NOT changing ANY of the bonds involved. The only things that are changing are the intermolecular bonding[/b'] of the molecules,

 

Those two bolded sentences seem like a contradiction... But yeah, I see those bonds are far weaker so I guess it is different.

-Thanks

 

The definition of an allotrope: differerent forms of the same element in the same state

 

I don't think that definition is correct, I just found this on wiki:

These phases of water are not allotropes, since they are caused by changes in the physical bonding between water molecules, rather than changes in the chemical bonding of the water molecules themselves. Allotropes of an element can be in any state, gaseous, liquid, or solid.

 

On another note...

What is the term for a molecular structure where two molecules share no bonds but are trapped together by their geometric stucture or their topology? Like an atom stuck in a buckyball or two cyclic carbon chains linked together. I wanted to look it up on the net but couldnt remember what they're called.

[YT2095]

just as a side note, Allotropes usualy always tend to refer to single elements alone rather than Molecules.

[LucidDreamer]

I don't think that definition is correct' date=' I just found this on wiki:

[i']These phases of water are not allotropes, since they are caused by changes in the physical bonding between water molecules, rather than changes in the chemical bonding of the water molecules themselves. Allotropes of an element can be in any state, gaseous, liquid, or solid.[/i]

.

Are you sure that the wiki definition is saying that a liquid can be an allotrope to a solid and not that two allotropes can exist in any one of the states?

[H2SO4]

i thought alltropes could only be liquids.

[LucidDreamer]

i thought alltropes could only be liquids.

I'm pretty sure that's wrong because graphite and diamond are allotropes.

[Yggdrasil]

i thought alltropes could only be liquids.

 

I think you're thinking about azeotropes.

 

http://en.wikipedia.org/wiki/Azeotrope

[jdurg]

Allotropes can ONLY be of a single, solitary element. There is no such thing as allotropes of molecules. Those are called isomers.

 

Moosie - there are two types of bonding. One is intramolecular bonding and that is what is responsible for keeping a molecule together. If you break the intramolecular bonding, you destroy the molecule. Intermolecular bonding is what attracts molecules to each other. Think of intramolecular bonding as the concrete that makes up a building, and intermolecular bonding as the suspension bridge that connects the two buildings. If you break the bridge, you still have the original buildings as they are. If you break the concrete, those buildings don't exist anymore.

 

So when I'm saying 'bonding', I'm really talking about the concrete and not the bridge.

 

Allotropes are also pretty much isolated to solids as well. I really don't know of any liquid allotropes since you really can't get a 'structure' out of a liquid.

[LucidDreamer]

Somebody should revise the wiki definition.

[BigMoosie]

I have read that sulfer can exist as different liquid allotropes: http://inst.santafe.cc.fl.us/~jbieber/chem/s_alltrp.html

[jdurg]

Those are the same allotropes as their solid forms.

[akcapr]

graphite, charcoal, diamond are allotropes

[H2SO4]

sorry, i meant arent all altopres are solids. What are aezeotropes? Kinda like alltropes but liquid?

[Yggdrasil]

An azeotrope is a mixture of liquids that cannot be separated by (simple) distilation (i.e. the mixture has a constant boiling point). An example is 95% ethanol/5% water. The concept is similar to that of a eutectic mixture except it relates to boiling point instead of melting point.

[H2SO4]

why do some chemicals form these aezeotropes tha cannot be seperated easily?

[insane_alien]

to give people who want to seperate them a hard time.