skeptic
Posts: 1163
Joined: May 2006
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| Quote (Louis @ Feb. 27 2008,10:37) | | Quote (Paul Flocken @ Feb. 27 2008,15:48) | | Does that mean the motions of atoms and molecules in space(to be sure, a very oversimplified definition of statistical mechanics) is not relevant to the organic chemistry of living things? Or, at least, minimally relevant? Louis? |
When I read this piece of Dave's my first thought is that Dave knows nothing about the physics or chemistry he pontificates upon. My second thoughts are less charitable.
The motions of atoms and molecules in space are VERY relevant to all chemistry. Of vastly greater relevance is the electronic nature of the atom/molecule in question. It's one of those things that you read and just throw your hands in the air and ask "where the fuck do I start?". I'm serious, where does anyone start with a person who is so utterly clueless about how atoms and molecules stick to each other or react. Where do we go? Huckel theory? Molecular dynamics and chemical reactivity? Spectroscopy? Quantum mechanics? Lattice field theories? I'm probably thinking too hard about this.
Do we want the Spot the Dog version of why molecules stick together for Davey?
A couple of simple things:
1) To a very rough first approximation, all chemistry boils down to the interactions of the valence electrons of atoms, and the interactions of certain pairs of electrons in molecules. This is incredibly oversimplified! So incredibly so I think it's more wrong than right but it will do!
2) If we're talking statistical dynamics a la Boltzmann etc, then the motions of a population of molecules for example is VASTLY significant to the chemistry those molecules will undergo. For two molecules to react there is a certain energy barrier, a resistance to this reaction, called the activation energy. A molecule must possess sufficient energy to overcome the activation energy barrier in order to react. At least part of that energy can come from the translational motion (i.e. the energy it has by virtue of moving) of the molecule, as well as other types (vibrational, rotational, electronic etc). There are even chemicals (i.e. not just materials) that react if you put pressure on them or poke them. It's a very cool area of chemistry.
3) If we're talking about the energy states of individual molecules (or atoms) when we talk about motion, then, as mentioned above, these are vital to what reactions the molecule can undergo but whether it will participate in any reaction at all. A simple example might be intramolecular cyclisations (i.e. the ends of a long chain like molecule joining together to make a ring). The motions of the molecule itself have enormous bearing on this. Consider the simple entropic aspects of the reaction, the longer and floppier the chain, the less likely it is those two ends will meet each other easily (and thus react and cyclise). It's much more complex than this involving a really profound understanding of molecular structure and orbital dynamics etc, but take it from me making a 24 membered ring is a lot harder than making a 5 membered ring in terms of the entropy (and a whole slew of other problems).
EDITTED TO ADD:
The Wikipedia article you quote is bang on in one sense. What it's talking about is actually quite important to the example of intramolecular cyclisation above. Imagine in your reaction flask you're attempting such a cyclisation, if the concentration of yout solution is wrong then the chances are the ends of the molecule you want to stick together are going to find an end from another molecule to stick to a lot quicker and easier than bending around on themselves to stick to their other end. If you get my drift. Polymerisation is the result (or at least oligomerisation). How and why things polymerise is, indeed, about more than the simple monomeric chemistry, like I said above, the thermodynamics of the system (in a global sense) has a big input. It's basically an ADDED problem. I wouldn't go as far to say that the behaviour (and certainly not the properties) of a polymer or a polymerisation reaction were in anyway independant from the chemical nature of the polymer, if only because modifying the chemical nature of the polymer can modify the degrees of freedom available to the system, and thus simplify/make more complex the problem. Think about the polymeric behavioural differences between polythene and teflon for example. Simple chemical change (F for H) radically alters the behaviour of the polymer in some sense. But granted without knowing precisely what they are referring to in that article it's hard to get anything useful out of such a generalisation.
The stuff from Dave is so confused I don't really know where to begin!
Louis |
Now this is the Louis that I know and love. :D Give 'em hell!
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