Molecules and compounds

[phl666]

What is the difference between a molecule and a compound?

[newtron]

A molecule is the smallest chunk of a certain substance that is still identifiable as that substance. In other words, to make this chunk any smaller, you would have to remove atoms and the substance would no longer be the substance you started with. A molecule of a compound is made up of more than one atom of different types, and a molecule of an element only has one type of atom.

[phl666]

I see, so:

O2 = Oxygen = Molecule
H2O = Water = Compound

Is that correct?

If so, why do we refer to "water molecules"? Is this an oxymoron?

[newtron]

You could have a molecule of a compound and of an element. A water molecule would be 2 hydrogen atoms bonded to an oxygen atom. Sorry if my answer was not very clear.

[lord molly]

newrton;

is an argon atom a molecule then? since it is not a diatomic gas, having a full outer shell of electrons it will not bond coveliantly or ionicly with anything?

[lord molly]

is a molocule of propane, rely a molecule then, as it can go on for ever since it can be polomerised?

[shammydodger]

Lord Molly

Argon is indeed a monatomic gas, as are the other noble gases. Molecules are made up of two or more atoms, chemically bonded together. So, no, an argon atom is not a molecule. The atoms in a molecule need not be the same, but often are, as Newtron correctly stated (in a different manner) in his/her initial post.
As for propane, this is a hydrocarbon with the chemical formula C3H8 and exists as discrete molecules. It cannot be polymerised, at least not in any way known to science, and still retain the chemical properties of propane. To put this another way, any polymerisation of propane, should it ever be found to be possible, would not still leave you with propane. Consider, for example, what the result would be of bringing two molecules of propane together and joining them �end-to-end�, kicking out a molecule of hydrogen at the same time. The result would have the chemical formula C6H14 and the structural formula of hexane. Indeed, it would be hexane, not �propane dimer� and have different properties to propane. For starter�s, hexane is a liquid at room temperature and propane is a gas.

Cont.

[shammydodger]

Lord Molly

cont.

I think you are getting confused as to what polymerisation actually is. Consider the simplest polymerisation, that of the hydrocarbon gas ethene (or ethylene, for our older ABers). The polymer formed from its polymerisation is polyethene (commonly known as polythene). I think you will agree that polythene has properties that are distinctly different from those of ethene.

Apologies if I�ve managed to confuse you further!

[wooohooo]

im doing that in science. its uber boring.. i think molecules are groups of one atom and a compound is a mixture of atoms that are chemically joined. ha thats probabaly completely wrong. sorry :( i should pay more attention is lesson

[wooohooo]

in*

[SarCaustic]

A molecule is two or more covalently bonded atoms. A compound is a molecule that comprises atoms of two or more elements.

[shammydodger]

Sarcaustic

Correct. And nothing different to what has already been posted (by Newtron as well as myself)

[Gef]

I'll try to clarify things and keep it simple.

A molecule is a group of two or more atoms joined by covalent bonds. The atoms can be the same (an element) or they can be different (a compound).

A compound is a single substance which contains different elements in fixed proprtions. They can be joined by either covalent or ionic bonds.