Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jsmith613 on September 02, 2009, 06:29:05 PM
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I know that a molecule consists of 1 or more atoms, but (this might sound like a stupid question), is diamond a molecule
My doubts come from here: http://wiki.answers.com/Q/How_many_carbon_atoms_make_up_one_diamond_molecule
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I do not have an answer, but I like the question.
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A friend of mine - back in eighties - did his MS calculating (QM) how many atoms are necessary for a crystal to behave like crystal. Not that I remember anything else :-/
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Well, diamond is a covalent crystal, so it's made up "only" (I use the quotes as perfect crystals are really rare and most of the crystals we get in touch with are actually full of imperfection, e.g. different atoms in the structure which sometimes give the compund a characteristic aspect, such as the color in some kinds of diamonds) of C atoms linked with covalent bonds.
So obviously we can think at it like a "giant molecule", even if it's more correct to consider it a crystal (also because we could only write Cn for its formula, as there are no fixed edeges for the atoms that can link together).
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I read somewhere that chemically it's almost exactly like graphite (in pencil "leads") but it's just structured a little differently and more densely.
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I read somewhere that chemically it's almost exactly like graphite (in pencil "leads") but it's just structured a little differently and more densely.
It is almost as precise as if you have stated that notebook after being squeezed in hydraulic press doesn't change - its elements are just structured a little bit differently and more densely.
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I read somewhere that chemically it's almost exactly like graphite (in pencil "leads") but it's just structured a little differently and more densely.
Well, in graphite there are "plane surfaces" made up of carbon atoms linked together with Van der Waals forces, which allow us to easily break those bonds and write with a pencil ;D
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Though you might not always be able to write with a pencil, you'll always be able to scratch your message with a diamond-tipped pen. ;)
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Diamonds is not a molecule, it's a covalent network of carbonds arranged in a way that allows the diamond to form it's properties
so is graphite, graphite is also covalent network but the carbon atoms in graphite are arranged differently.
http://www.avogadro.co.uk/structure/chemstruc/network/g-molecular.htm
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@kunjal8015
So according to your definition is H2 a molecule
Can you compare and contrast this with a diamond
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I would consider it a molecule. If you are going more in depth you can most likely call it something else but it is a molecule.
Wouldn't the basic definition of molecule be ..2 or more atoms?
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@Ida Isotope -
What is a mixture?
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I know from Materials chemistry that diamond is classified as a covalent solid, something similar to a form of phosphorus (i cant remember which one). I guess the arguments in this thread depends on what the accepted definitions of a molecule, mixture etc are...but a the end of the day, that is more philosophical, and really, of no importance, as long as we know what is actually going on inside the diamond, or any other structure for that matter. ;)
But since we are on the topic of diamonds...a question...if diamond consists of a network of tetrahedral carbon atoms bonded to 4 other tetrahedral carbon atoms, what is happening at the surface of a diamond crystal? Just something I have pondered before... ???
Steve
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but a the end of the day, that is more philosophical, and really, of no importance,
Philosophically speaking I would tend to disagree
;D
For instance when we do calculations involving hydrogen there are times we have to look at it as H2 rather than H
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@Ida Isotope -
What is a mixture?
It is when 2 or more different subjects are "mixed" or combined. Not mixed chemically though.
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I would consider it a molecule. If you are going more in depth you can most likely call it something else but it is a molecule.
Wouldn't the basic definition of molecule be ..2 or more atoms?
Yes that is what a molecule is, but i just never though of diamond as being a molecule, and as you say at surface level it is, but what is it a little deeper than that?
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Is graphite a molecule also?
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I don't think so... it's composed of layers of graphene and if we ask ourselves if graphene is or not a molecule I think there's the same "philosophical" (;D) problem encountered with diamond...
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Won't diamond be classified as a crystal because it contains a unit cell in its structure? I know many inorganic solids that have unit cells such as sodium chloride are not considered molecules while other compounds that lack unit cells such as H2 are considered molecules. It is an interesting question, and it makes me wonder where the lines are officially drawn between the different types.
I guess the arguments in this thread depends on what the accepted definitions of a molecule, mixture etc are
Yeah, that's at the core of the issue I think. Nature just is how she is; we're the ones constantly getting frustrated trying to describe her.
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Apparently someone's missing something, yes, graphite and diamond are both carbon-bonded compounds, but the two differ in the type of bonding. Graphite bonds extends in a linear (or 2D) direction, the final structure is made up of layers upon layers of graphene (as MrTeo have pointed out) that rub off of eachother when you write with a pencil. Because paper is made up of cellulose, it binds to the layers of graphene tighter than the layers of graphene bind to each other.
Now, back to diamonds. I would say that a diamond might be a molecule, depends on how closely you want to look. If we consider "pure" diamond, as in absolutly pure, all carbon, no metal ligand (metal ions) of any kind trapped inside the crystal formation, then yes, the diamond is just one gigantic molecule. Unfortunately, most diamonds are not pure, stuff gets trapped inside, in more extreme cases, they actually change the colour of the diamond (such as the Hope Diamond, it has too much boron inside it, or chocolate diamonds, which has too much nickel). In most cases, you could say that a diamond is a mixture, though the carbon crystal structure that holds the entire thing together could be considered as one molecule.
One more thing, the tetrahedral carbon-carbon structure, although very rigid, is also a bit unstable. Remember that diamonds are formed under intense heat and pressure (so the notebook under the press idea, no; notebook under the press in an oven might work though), but on the earth's surface you don't have these conditions, so the diamond structure is shifting back to its original form, graphite, abide extremely slowly, though the process is spontaneous (i.e. exothermic, will happen without outside interference). I once did a calculation on the decomposition of diamond :rarrow: graphite, it turned out that for one gram of diamond to fully decompose into one gram of graphite, in completely isolated condition, takes around 2.4 billion years and gives off 4.7J of energy in heat, so yea, don't have to worry about waking up one day to find your wedding ring had turned into pencil lead.
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A friend of mine - back in eighties - did his MS calculating (QM) how many atoms are necessary for a crystal to behave like crystal. Not that I remember anything else :-/
Crystallographers think about crystals if it show at least 3x3x3 ordered unit cells.
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I think the problem here is more semantics than chemistry. A diamond can be considered a single molecule (an electrically neutral group of two or more atoms held together by covalent chemical bonds), but has properties of a crystal (repeating pattern extending in all three spatial dimensions).
But those are just words which do not completely describe what diamond is. Is it both molecule and crystal at same time or should it be called something else, a covalent solid, a covalent crystal, a diamond...
It's like asking is neutron star a single atom?
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Diamond is a polymer, a very large molecule made up of repeating subunits. A single diamond could in fact be all one molecule, just like a single bead of polyethylene could be all one molecule. It is not, strictly speaking, a crystal, because a crystal contains multiple molecules, atoms, or ions in a repeating, ordered array.
Graphite is also a polymer, but the graphene structure forms two dimensional sheets rather than three dimensional lattices. Each layer of graphite can be a single molecule, but a chunk of graphite large enough to examine would have an enormous number of layers, each one atom thick, of graphene "molecules". A chunk of diamond large enough to examine, if it was completely pure, could still be a single molecule, since diamond has a three dimensional structure.
Polyethylene, the third polymeric form of carbon, is a linear structure. Since the structure is not rigid, like graphite or diamond, a bead of polyethylene containing a single molecule would be very much like a ball of string. Or rather, a tangle of string containing a single thread, since balls of string are usually much more ordered.
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This is all thanks to Carbon being such an annoying element, with annoying, chain forming, covalent bonding, life making properties.
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Polyethylene, the third polymeric form of carbon, is a linear structure. Since the structure is not rigid, like graphite or diamond, a bead of polyethylene containing a single molecule would be very much like a ball of string. Or rather, a tangle of string containing a single thread, since balls of string are usually much more ordered.
I don't understand? Polyethylene has hydrogen, how is it the third polymeric form of carbon?
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All of the polymeric forms of carbon (diamond, graphite, and polyethylene) have hydrogen attached to carbon at any site on carbon which does not already have a carbon-carbon bond. On diamond, this occurs on the perimeter of the solid, on graphene it appears on the edges of each sheet.
Actually, to completely fill out the model, conjugated polyalkenes (polyacetylene) and polyalkynes would also have to be included as single-molecule polymers of carbon, although these are far less stable than the three previously mentioned.
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I know that a molecule consists of 1 or more atoms, but (this might sound like a stupid question), is diamond a molecule
My doubts come from here: http://wiki.answers.com/Q/How_many_carbon_atoms_make_up_one_diamond_molecule
According to IUPAC a molecule is defined as
An electrically neutral entity consisting of more than one atom (n > 1). Rigorously, a molecule, in which n > 1 must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state.
This definition is satisfied by diamond, therefore it is a molecule. More concretely diamond is often considered a typical example of (inorganic) macromolecule:
http://www.science.uwaterloo.ca/~cchieh/cact/applychem/macromolecule.html
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All of the polymeric forms of carbon (diamond, graphite, and polyethylene) have hydrogen attached to carbon at any site on carbon which does not already have a carbon-carbon bond. On diamond, this occurs on the perimeter of the solid, on graphene it appears on the edges of each sheet.
Actually, to completely fill out the model, conjugated polyalkenes (polyacetylene) and polyalkynes would also have to be included as single-molecule polymers of carbon, although these are far less stable than the three previously mentioned.
I though that diamond and graphite and amorphous carbon were allotropes.
polyethylene is a polymer. Hydrogen is part of the molecular structure. You can't have polyethylene without the CH2 units.
There is also another allotrope that was discovered recently. It is similar to diamond but has a boat shape alignment.
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Yes diamond is a molecule.
You can consider 02 to be a molecule as it is conbined by 2 oxygen atoms therefore a diamond which is a cobination of multiply carbon atoms is by extension termed to be a molecule.
Thanks,
DDZ and ZC