The Science Thread

[Corribus]

Alright, now what was the question again? Ah yes, how do molecules react.

Here's my brief (following my stretched definition of "brief") explanation.

Start with the scenario of a ball rolling down a hill. Why does it do so? Gravity, yes, but why? There are a number of ways to look at the problem but one of the most elegant is a thermodynamical explanation. A ball sitting atop a hill has some quantity of potential energy, a "high energy position". Potential energy is essentially a term that means "has energy to put elsewhere". At the bottom of the hill, once the ball has rolled, the energy has been dispersed. We call this a low-energy position. But why does the ball go from a high energy position to a low energy position? This is a thermodynamically favorable process, driven at least partially by the fact that the process "degrades" the potential energy into "less-useful" forms. Those are imprecise terms but sort of embody one of the ways some physicists like to define changes in entropy. You can kind of think of it like this: a ball sitting on top of a hill has all this potential energy bunched up in one place just waiting to do something. As the ball rolls down the hill, this energy is converted into kinetic energy, it's converted into heat (friction), sound, etc., all sorts of energy that eventually get dispersed throughout the environment and the rest of the universe. This is sort of another way of saying "order is decreased". Entropy. It's a bit more complicated than that but.. well it's also sufficient. This sort of framework also helps to understand reaction dynamics. Also if you plot out potential energy by some sort of position coordinate, it can be shown that this is related mathematically (by derivative) to a driving force, a term which is used very often in physical chemistry.

So, there is this natural inclination of balls sitting on hills, and molecules/chemical systems as it turns out, to go from high-energy, ordered states to low-energy, disordered states. These two energetic contributions (enthalpy and entropy) go together (along with temperature) to form in chemical terms what is known as the Gibbs energy, which is sort of a "chemical potential energy", or, the amount of energy a chemical system has to do useful work. Any chemical process which has a negative change in the Gibbs energy (delta G < 0) is analogous to a ball rolling down the hill - chemists call it a spontaneous reaction. That is, it will happen - in principle - with no external stimulus or energy applied to the system. These sorts of processes are also called "exothermic" because that energy that is released is released as heat energy (exo + thermic = heat out). Physicists are often unclear about what, exactly, heat is - they like to complicate everything - but one convenient way to look at is that it is friction caused by molecules/particles bumping into each other when they move. So, when reactions "roll down the hill", that Gibbs energy is often at least partially turned into translational motion (kinetic energy) which manifests itself macroscopically as heat.

Alright, enough of intro to thermo.

Now what you need to understand is that every molecule has some potential energy. This is based on an arbitrary scale - rather it is a value that only has meaning relative to the energies of other molecules - but for any given molecule this is a combination of a lot of things, in particular energies of bonds and of molecular structural factors. In condensed phases, you also have to take into consideration any interaction between the molecule of consideration and any other molecules nearby. Note that this also applies to atoms. For instance, with the exclusion of some exceptions (e.g., noble gasses) you rarely find atoms floating around merrily on their own. Why? Naked atoms have large potential energy because they almost invariably have unpaired electrons. For QM reasons which I can elaborate on if you wish, atomic systems are lower
energy (we call it "more happy") if they possess full sets (precisely, if they possess full shells) of paired electrons. So as it turns out ions are lower energy species than atoms in most cases. Depending on the atom in question, it may be easier to give up (oxidize) or acquire (reduce) the atom to attain this state. So atoms which float by each other will almost immediately react toform molecules by electron exchange (redox reactions, usually forming salts) or sharing them (forming molecules). A good example is table salt. Sodium has one electron too many and chloride one electron too few. Together they have a relatively high potential energy compared to sodium cation (Na+) and chloride anion (Cl-) and so a reaction between them (the atoms) would be fast and spontaneous. When such a process happens, energy is released to the environment and some is stored in chemical bonds. Why chemical bonds instead of free ions? Because while ions are happy, molecules
are happier - because ions are also charged and free charges, compared to paired (opposite) charges, are "high energy" (why do you think this is so?). Note that you are able to solubilize free ions in solution (such as dissolving table salt in water) because water, which is polar, helps to lower the potential energy of individual charges. You cannot dissolve table salt in nonpolar solvents (like gasoline) because the potential energy of free ions is too high, and so the ionic network of chlorides and sodium cations in a solid crystal lattice is the observed lowest-energy product in this case.

Again, everything is driven by relative energy and seeking out the lowest energy state.

To be continued...

[winterfate]

@Corribus: NICE!!

I really enjoyed it! Very very insightful!

Entropy.

I was reading in my Biology textbook that the universe will end in heat death eventually (as in billions of years from now eventually), due to the fact that heat is a waste product of energy processes and heat as an energy source is inefficient.

What happens to the universe after that? Interesting question indeed.

A good example is table salt. Sodium has one electron too many and chloride one electron too few. Together they have a relatively high potential energy compared to sodium cation (Na+) and chloride anion (Cl-) and so a reaction between them (the atoms) would be fast and spontaneous.

And otherwise both sodium and chloride are poisonous gases in their base form.
I like to think I know a thing or two about chemistry too.

because ions are also charged and free charges, compared to paired (opposite) charges, are "high energy" (why do you think this is so?)

Hmm...does it have anything to do with the fact that positive and negative energies cancel each other out? (become neutral)

[Corribus]

I was reading in my Biology textbook that the universe will end in heat death eventually (as in billions of years from now eventually), due to the fact that heat is a waste product of energy processes and heat as an energy source is inefficient.

That is one theory, but it's no longer the only accepted one. There's a term called omega which relates to the density of the universe. If it is on one side of one, you get heat death (expansion accelerates infinitely). If it is on the other side of one, expansion stops and you get collapse (the big crush). And if it equals one exactly you get another sort of heat death. You might try looking up "Big Crunch" or "Dark Matter" in wikipedia.

And otherwise both sodium and chloride are poisonous gases in their base form.

Chlorine is a poisonous gas (used in WWI as a chemical weapon) - but it's Cl2, not atomic chlorine. Sodium is a solid metal that has a tendency to burst into flame (due to oxidation with water) if it's not stored under mineral oil.

Hmm...does it have anything to do with the fact that positive and negative energies cancel each other out? (become neutral)

In a way, yes. The charges do balance out when they are paired. The reason free charges are high energy in most media is because there are electrostatic forces which disturb the surroundings. When dissolved in a polar solvent, free ions are stabilized, however. For instance, in water because water is polar, water molecules can order themselves around the free charge and form "hydration spheres" which serves to delocalize the charge over a larger area and make it less...er... disruptive. Water is actually quite an impressive molecule and it is properties like this that make it so important for life.

[winterfate]

Chlorine is a poisonous gas (used in WWI as a chemical weapon) - but it's Cl2, not atomic chlorine. Sodium is a solid metal that has a tendency to burst into flame (due to oxidation with water) if it's not stored under mineral oil.

Sodium is a metal...oh...
I did know that chlorine was a gas though!

That is one theory, but it's no longer the only accepted one. There's a term called omega which relates to the density of the universe. If it is on one side of one, you get heat death (expansion accelerates infinitely). If it is on the other side of one, expansion stops and you get collapse (the big crush). And if it equals one exactly you get another sort of heat death. You might try looking up "Big Crunch" or "Dark Matter" in wikipedia.

Woah...so there's no way to stop it then? There isn't some sort of anti-entropy?

In a way, yes. The charges do balance out when they are paired. The reason free charges are high energy in most media is because there are electrostatic forces which disturb the surroundings. When dissolved in a polar solvent, free ions are stabilized, however. For instance, in water because water is polar, water molecules can order themselves around the free charge and form "hydration spheres" which serves to delocalize the charge over a larger area and make it less...er... disruptive. Water is actually quite an impressive molecule and it is properties like this that make it so important for life.

And its ability to form hydrogen bridges (not 100% if that's how you say it in English...have to check textbook later to verify). Surface tension and other such things too...its one of the first things we covered in Biology I...for without water there can be no life (the few organisms that could survive without water are bacteria that use fermentation instead of aerobic respiration for energy).



I love this thread!

[Corribus]

We call them hydrogen bonds but I understand your meaning.

[winterfate]

Ah there we go, hydrogen bonds. Thanks Corribus!

It's kind of funny how most of the textbooks are in English...severe disadvantage if you aren't fluent in English. Gotta love those 12 years I was in the States!

I hope I'm not being a bother. I'm sure you have lots of things you could be doing right now, besides indulging a microbiologist-to-be on the finer arts of chemistry.

[Corribus]

So, on to molecules. The molecular potential energy is, as I said, a function of many variables. For the time being, we can restrict the discussion to gas-phase reactions, in which, to an approximation, intrinsic molecular energy is determined only by intramolecular considerations: i.e., molecular structure. Molecules now are too far apart to be, on average, influencing each other. Molecular structure plays a large role in determining reactivity. For instance, there is a class of ethers called epoxides which are highly strained. Due to QM considerations, molecules prefer to bond in certain ways, and angles and lengths between certain atomic configurations tend to prefer certain values. (This of course, has to do with finding the "lowest energy" conformation.) So when I say "highly strained" I mean that the epoxide features bond angles that are quite far removed from what carbon-carbon-oxygen bond angles would normally prefer. So if your reactant is an epoxide and your product is the normal products of combustion (i.e., water and carbon dioxide) which we know are quite stable, you can imagine that this reaction is quite favorable AND due to the difference in energy of the starting material and the final products, gives off a lot of heat. Point of fact: epoxides are quite dangerous and explosive, and that's due to potential energy stored in the highly strained epoxide structure. It's sort of like a spring that compressed really tightly - give it a chance and it will try to release that energy.

Back to gasses. Let's consider the most simple case of two atoms, initially far apart, that speed towards each other. What happens?

We can make a lot of predictions in statistical mechanics and quantum mechanics using what are called potential energy surfaces. Sounds sophisticated but it's really no more than plotting out the potential energy of your system as a function of position. For a ball rolling down a hill, in the X direction, your potential energy surface would look something like the shape of the hill. In complex systems, potential energy surfaces are generally many dimensions in space, and so they can be hard to visualize, but in a diatomic system, it's quite easy. Since potential energy is relative, we can set the potential energy of two isolated atoms as an arbitrary zero point. Then we can plot the energy of the two atom system as a function of the distance between them. One of the best functions that simply models a potential interaction is the so-called Morse potential. It looks like this:



Don't worry about the red lines right now. Only the blue is important. This is your potential energy surface. The X axis is your intermolecular distance. The Y axis is an energy axis. If you think about it, the shape makes pretty good sense. Focus on the limits first. As X = very large, the function sort of assymptotically approaches some limiting value. I defined as 0, and the figure defines it as 1. It doesn't really matter. What's important is the concept: obviouslly as you bring the two atoms further and further apart from one another, they feel each other less and less. Interactions between atoms are electrostatic in nature, and you know that the Coulomb force falls off with distance. (The force experienced between the two atoms can be determined quantitatively by taking the derivative of the potential function. You can show this using some very basic physics equations.) Anyway - so as you bring these two atoms closer together, they begin to attract one another.

(tangent: the fact that they attract one another to form a bond should strike you as odd. The electron clouds of each atom are quite repulsive to one another, and yet, defying logic, they actually feel an attractive force. That, my friend, is just one of the bizarre consequences of quantum mechanics that really has not parallel in the macroscopic world. This phenomenon is maybe best described as a consequence of the ability of electron position to be ill-defined due to Heisenberg Uncertainty and the bonding electron on the first atom to actually be part of the second atom, and vice-versa, at the same time. If that sounds weird and poorly described by me, it is. )

As you bring the atoms together, they attract and the potential energy of the system is stabilized significantly. You eventually reach an energetic minimum (this is the equilibrium bond length) and then as you bring them even closer, the potential energy sky-rockets to infinity. You can imagine that this is because two atoms can't occupy the same space at the same time. Coulombic repulsion also may start to dominate.

Of course, the potential energy is only half of the equation. It does not reflect the total energy of the system. The atoms are moving and have kinetic energy as well. The total energy is the kinetic energy plus the potential energy and so the real energy of the system always (well... in classical physics) is higher than the potential energy. The kinetic energy is of course related to the temperate of the system.

So now you are ready. If it helps, imagine one of your atoms to be stationary and the other to be moving towards it with some speed. Remember that total energy is always conserved. So as your moving atom moves towards the stationary one, the total energy is slightly above the blue line by some finite amount - and has to stay at the value unless some energy can be removed from the system. As the atoms get closer to one another, the attractive force gets larger, the potential energy drops (more favorable "structure"), and because the total energy must remain constant, the moving atom speeds up, much like a ball rolling down a hill. Faster it goes (but your total energy is still way above your assymptotic limit!) until it passes through the minimum and "smashes against the potential barrier" at small interatomic distance. At this point the system may LOOK like a molecule, but it is not. Because energy is conserved, the collision with the potential barrier is sort of like two billiard balls smacking into each other. They bounce off each other and go merrily on their way until they exit stage right with essentially the same total energy that they had when they started.

Boring.

So the only way for the diatomic molecule to form is if, when the moving atoms are at an appropriate distance that they are above the "well", a third, spectator atom or molecule collides with the excited complex. By transfering some of that energy to the spectator (which then goes merrily on its way), the system loses energy. If it loses enough so that it is below the assymptotic limit of two isolated atoms, it becomes trapped in the well and starts to bounce back and forth between the two walls, sort of like a spring. Bonds behave this way. This is now referred to as a bound system. Congratulations, you have a baby molecule.

Notice the red lines in the figure. These represent so-called vibrational states. As it turns out, the laws of QM dictate that only certain vibrational energies are allowed for small particles, and these are depicted by the figure. As you approach the "dissociation limit", which is the energetic limit at which, given that much energy, the atoms can fly apart, the vibraitonal states get infinitely close together. A vibrating molecule is easy to visualize using this figure. The red line represents the total energy of the molecule in that vibrational state. The blue represents (classically) the bond at its most compressed and least compressent limits. At this point, the total energy equals the potential energy and the atoms are not in motion. Then they go back the other way, through the mid-point - where the potential energy is the lowest but the kinetric energy is the highest - back toward the other limit. And so on. If the molecule exists in a vacuum, this would happen indefinitely because there would be no avenue for the molecule to lose energy. Eventually, through enough collisions, the new molecule can rest in the lowest vibrational state (indicated by V0). Notice that the zero level is not at the bottom of the well. This is another peculiarity of QM. A molecule is a spring that can never stop springing back and forth - there is always, no matter how cold, vibrational motion, a latent energy that cannot be removed from the system.

(Two additional points: (1) There are also rotational states, and these, like the vibrational states, are restricted to certain energy. Each vibrational state is associated with a set of rotational states. (2) The blue line represents the classical limit of vibration because if the spring were to extend beyond that limit, there would be more potential energy than total energy, which is not allowed. Actually though there is a phenomenon called tunnelling which means that, in QM, this CAN be allowed, although the probability drops off FAST as a function of particle size. Unless you're dealing with protons or smaller, it's pretty insignificant. But it is actually very significant for biology - you wouldn't be alive without it. And it's kind of a cool concept, to think that the spring can actually be more stretched out than, classically, it should be allowed to be.)

The depth of this well depends highly on the nature of the atoms involved. The more stable the molecule, the deeper the well. Not all groups of atoms form molecules. Note that ALL molecules have potential energy wells - it is just that it may take 100s of dimensions to plot them out.

Alright that's enough for now. I'm going on vacation tomorrow so I'll let you digest that for a while winterfate. When I get back, I will get to the interesting stuff. Reactions between molecules rather than just simple molecular formation, reaction kinetics, and then tie that into statistical mechanics, which is essentially the statistical behavior of large groups of molecules.

Which of course will bring us finally to the primordial soup.

[winterfate]

Alright that's enough for now. I'm going on vacation tomorrow so I'll let you digest that for a while winterfate. When I get back, I will get to the interesting stuff. Reactions between molecules rather than just simple molecular formation, reaction kinetics, and then tie that into statistical mechanics, which is essentially the statistical behavior of large groups of molecules.

Sure thing! It's a lot to digest! I should understand it by the time you get back.

Thanks Corribus. Have fun on your vacation!

[Gaidal Cain]

Physicists are often unclear about what, exactly, heat is - they like to complicate everything - but one convenient way to look at is that it is friction caused by molecules/particles bumping into each other when they move.

Heat's easy: it's energy. You should see what Temperature looks like though.

That is one theory, but it's no longer the only accepted one. There's a term called omega which relates to the density of the universe. If it is on one side of one, you get heat death (expansion accelerates infinitely). If it is on the other side of one, expansion stops and you get collapse (the big crush). And if it equals one exactly you get another sort of heat death. You might try looking up "Big Crunch" or "Dark Matter" in wikipedia.

I think it's pretty widely accepted by now that the universe will continue expanding forever. Dark energy takes care of that.

Interactions between atoms are electrostatic in nature, and you know that the Coulomb force falls off with distance.

Not to mention the fact that atoms are neutral on average, and you need to get really close to "see" the difference between the core and the electrons.

This phenomenon is maybe best described as a consequence of the ability of electron position to be ill-defined due to Heisenberg Uncertainty and the bonding electron on the first atom to actually be part of the second atom, and vice-versa, at the same time.

It's actually a bit simpler to understand for the noble gases, where the bonding comes from fluctuations in the electron cloud (if you've ever seen a figure where atoms go in nice orbits around the core, forget about it. That's a simplistic picture from when quantum physics where young and we didn't really know how strange it really is. Electrons move around very randomly, even though they on average do tend to be close to those orbits). A fluctuation in one atom would mean that there is on average a little less or a little more charge on the side that's facing the other one. the electrons there would notice this, and move towards or away from it, depending on which it is. This would form a very, very weak bond between the atoms- so weak it almost doesn't matter. This is called a van der Waals bond. It happens for larger molecules as well, where it might be a good deal stronger.

Because energy is conserved, the collision with the potential barrier is sort of like two billiard balls smacking into each other. They bounce off each other and go merrily on their way until they exit stage right with essentially the same total energy that they had when they started.

Actually, this is quite wrong. As you've pointed out, there are several internal degrees of freedom in the molecule (this basically means "several ways for the molecule to store energy in itself"), and the whole molecule could also start to move at a lower speed. It's in fact another quantity that's preserved that means that a third atom or molecule has to be involved: momentum (since there are no external forces on the atoms). Kinetic energy is quadratic in speed, and momentum is linear in velocity (Notice the terms "speed" and "velocity". There is a reason for them, but it's sort of involved.). This means that ultimately, you can't just smash the two atoms together and have them continue moving at a lower speed, because a speed that would conserve energy wouldn't conserve momentum. And since it's energy that's quadratic, conserving momentum would mean that you'd need to get new energy from somewhere.

[Corribus]

Heat's easy: it's energy.

Isn't that what I said?

I think it's pretty widely accepted by now that the universe will continue expanding forever. Dark energy takes care of that.

Really? I was under the impression it was still very much debated.

It's actually a bit simpler to understand for the noble gases, where the bonding comes from fluctuations in the electron cloud (if you've ever seen a figure where atoms go in nice orbits around the core, forget about it. That's a simplistic picture from when quantum physics where young and we didn't really know how strange it really is. Electrons move around very randomly, even though they on average do tend to be close to those orbits). A fluctuation in one atom would mean that there is on average a little less or a little more charge on the side that's facing the other one. the electrons there would notice this, and move towards or away from it, depending on which it is. This would form a very, very weak bond between the atoms- so weak it almost doesn't matter. This is called a van der Waals bond. It happens for larger molecules as well, where it might be a good deal stronger.

van der Waals aren't typically strong enough to hold atoms together at ambient temperatures, although they do have quite an impact on bulk molecular properties (such as, for instance, boiling point). They are also more relevant in condensed phases where molecules are closer together.

Noble gasses do not typically form diatomic molecules at ambient temperatures either, for this reason. There may be a potential well formed by van der Waals forces but it's in most cases too shallow to trap anything due to latent (heat) energy. Although, diatomic noble gasses DO exist - if you oxidize the complex you can actually form an attracitve well that will trap the species in molecular form. But... I was trying to keep this simple.

And since it's energy that's quadratic, conserving momentum would mean that you'd need to get new energy from somewhere.

Energy and momentum are related. It's too ways of looking at the same coin.

And now I'm really off.

[Gaidal Cain]

Energy and momentum are related. It's too ways of looking at the same coin.

Well, if you consider time and space to be the same thing, so OK. Most people don't, so then it's to oversimplify things.

[Corribus]

Well, if you consider time and space to be the same thing, so OK. Most people don't, so then it's to oversimplify things.

The main goal in this thread will be to keep things simple. Most people without formal training in physical sciences cannot easily visualize the funneling of energy through various vibrational/rotational/translational degrees of freedom that necessarily accompanies any molecular energetic relaxation process.

What they can visualize are classical analogies that, while perhaps not completely accurate, at least preserve the spirit of what is going on a quantum level. There is a fundamental challenge in describing quantum phenomena using classical terminology. Treating colliding atoms like billiard balls elastically transferring kinetic energy (or momentum) is certainly not a completely realistic picture of what is going on, but most people are familiar enough with the concept from every day life that they can use it as a starting point to see what is going on in colliding atoms and reacting molecules in the gas phase.

In truth, GC is correct that momentum is a better variable to use as in reality collisions between atoms are not perfectly elastic and kinetic energy is NOT necessarily conserved - some kinetic energy can be stored internally in the molecule. For that matter, atoms aren't hard spheres either, and billiard balls doesn't have electrostatic forces that cause them to stick together. But in the interest of answering winterfate's question without invoking too much complexity, the kinetic energy argument is simple and classically appealing and makes sense on a superficial level.

The take home point - in the classical sense - is that in most cases atoms or small molecules in motion in the gas phase are too energetic to form stable complexes (i.e., bigger molecules) unless some of that excess energy is transferred elsewhere. It's really secondary to the question at hand, though.

More to follow.

[Caradoc]

In some of the murkier depths of the Internet, I have come across references to something called monatomic gold, which takes on a white powder form. "In monatomic gold, the electrons in the outer shells re-arrange from 5d^10 6s^1 to 5d^9 6s^2 leaving a hole in the 5d orbital. The nucleons move into higher energy shells, and the nucleus becomes elongated and begins to spin." There appears to be some experimental evidence that this can happen. And a lot of speculation on the marvelous properties of such a substance. Could there be anything to this?

[Corribus]

I have not heard of such a substance, and I'm usually pretty on top of the latest in pseudoscience.

A quick google search leads me to feel that this is a typical case of people taking real scientific findings and extrapolating them to ridiculous conclusions and using them as "evidence" to support their claims about the amazing properties of weakly-connected commercial products.

Some explanations of terminology - read if you wish:

High spin states, particularly for electrons, are nothing unusual. A simple example is in diatomic oxygen. Each electron has an associated "spin" which can be classically thought of as analogous to the angular momentum of a spinning sphere. As is typical of quantum phenomena, electron spins can only assume certain values (two, in fact, assigned "ms" values of +1/2 and -1/2, which have the same energy). The total spin magnitude for an atom or molecule is equal to the sum of all the individual electron spins to be considered. In a hydrogen atom, which only has one electron, said electron can have only a ms value of 1/2 or -1/2, and so the total (Ms) values are 1/2 or -1/2, and the total (absolute magnitude) spin angular momentum (S) is equal to 1/2. Often a quantity called the "multiplicity" is defined as M = 2S + 1, and so we say the spin multiplicity of a hydrogen atom is 2, or that it exists in a "doublet" spin state, a state which is characteristic of any atom/molecule with a single unpaired electron. In all orbitals there can only be at most two electrons, and if said orbital is filled to capacity, the two electrons must necessarily have opposite spins, and so any filled orbital has a total spin-momentum (S) equal to zero because the individual angular momenta cancel. diatomic oxygen is peculiar in that it has two unpaired electrons, giving it a total spin of 1, and the lowest energy spin multiplicity state is called a triplet. It is possible to excite one of these electrons so that it pairs with the other, forming a spin-state with no spin momentum, or a singlet. The stable triplet is a "high spin state" and the excited singlet is called a "low spin state". The reason these states have different energies is that each isolated spin generates magnetic/electric fields associated with the electron's intrinsic spin angular momentum and its charge. As a result, when electrons are located in close proximity to each other, there is a resulting interaction energy. All other things being equal, higher spin states are more stable than low spin states for electrons located in orbitals have the same energy. Actually spin states are very important in biology - the electronic spin states of iron are responsible for the binding and releasing of oxygen in hemoglobin.

Like electrons, nuclei have spin states as well, although not being fermions themselves (though they're made up of fermions) they may take on values other than just +1/2 and -1/2. Nevertheless, if two nuclei could be brought into close enough proximity, their nuclear spins would interact in an analogous fashion, giving rise to nuclear spin states as well. However, you'd have to be able to bring the nuclei close enough together to observe an interaction, which could be difficult without the existence of bonding electrons to mediate the effect. Incidently, MRI utilizes the nuclear spin states of water to make images of your body. Nuclear spin states are excited all the time every time you step into an MRI machine!

Gold does not exist, under normal circumstances, as discreet atoms for substantial lengths of time. Either it forms ionic complexes (salts) OR it forms metal solids. When in metallic form, the nuclei sort of just sit there and the electrons sort of flow freely among them, which is why metals are conductive. If you could some how eject a single gold atom from the surface of the metal, it would eventually ionize and form a salt, probably with oxygen - although gold is very difficult to ionize which is why it is always shiny (doesn't tarnish easily) and very nice for jewelry. And even if it didn't (say, if you were in outer space) I'm not convinced there would be anything that spectacular about it. If you break gold metal (or most homogeneous substances, as well) into small enough pieces (think, 10s of nanometers scale), you DO get some bizarre effects due to what is called "quantum confinement" of electrons. Such is the basis of much nanotechnology research. I would be happy to elaborate as it is a topic that is much near and dear to my heart at the moment.

Anyway:

Some webpages having to do with so-callled "monatomic gold" cite some research where physicists were able to prepare complexes of 2 or so gold atoms that seem to collide together. This seems to have been done using some high energy experiments, my guess is probably in vacuum I guess in principle if you were able to bring two high energy gold nuclei in close enough proximity to form some sort of high energy complex, you could observe some coupling of the respective nuclear spins and form a "high spin state", which you might be able to refer to as "elongated". Given that such stuff seems to have been reported in scientific american, I have no doubt that the original work was true. Unfortunately, such complexes were reported to last only a fraction of a second, not surprising given how much energy it appears was required to manufacture them. I did not track down the SciAm articles, so I'm not familiar with the details.

Reading over some of the articles on this mysterious substance, I note a lot of jargon is thrown around, most of which is very outdated (we know a lot more about nanomaterials now than in the early 1990s) and much of which is irrelevant. Even if you could chemically "re-arrange" the valence electrons of a single gold atom, a species which would be short-lived, it is unclear to me how this would have any impact on the structure of the nucleus. Nuclei and electrons exist in very different worlds and exert only indirect influence over each other. Well, I should rephrase: Electronic structure DOES greatly affect nuclear configuration, but only in the way one nucleus is oriented with respect to another (i.e., molecular structure). Nuclear structure can also affect electronic structure by changing the degree of interaction between electron spin momenta and electron orbital momenta. But, while I am not a nuclear physicist, I just don't see any physical reason why the electronic configuration of a single gold atom - which you could change using light energy - would exert any major influence over the internal structure of the nucleus, certainly not before the timescale of relaxation to the stable electron configuration has occurred

Given that I can't find anything like this on any credible website, I think it's a hoax.

Hmmm... sorry if that was way more information than you wanted.

[Gaidal Cain]

The nucleons move into higher energy shells, and the nucleus becomes elongated and begins to spin.

There are some nuclei (=compounds of nucleons) that have elongated shapes and can spin (as in the classical definition of the word). I do believe it takes nuclei with higher mass than you can get with gold that won't decay over nanoseconds to be able to do that, though.

[winterfate]

Such is the basis of much nanotechnology research. I would be happy to elaborate as it is a topic that is much near and dear to my heart at the moment.

I read your spin explanation...very intriguing.

As for the quoted part, please do! Nanotechnology is cool!

[Ethric]

And here we are!

Corribus, I believe it's your turn.

[Corribus]

Alright 'Fate. I haven't had too much time this week, but just to let you know I haven't forgot about you, I'll post a little teaser here.

Of course, asking someone to tell you about nanomaterials is a little bit like asking someone to tell you about fish. There are a lot of different types of fish, just as there are a lot of different types of nanomaterials, and they are all interesting for different reasons. So really we kind of have to narrow it down a bit and focus the discussion.

Now let's just get a few nomenclatural things out of the way first. "Materials" is sort of one of those words that people use right now a lot because it's trendy, but doesn't really mean anything. What is a material? Well, anything can be a material. I mean, you probably usually think of materials as things like plastic, fibers, concrete, that sort of thing. And that's kind of the classical definition, but with the renaissance of materials chemistry due to the advent of polymers and nanoscale structures, materials has become a word used to encompass a lot more than just "stuff things are made of". For instance, what used to be called "molecules" are now, in scientific jargon, referred to as "materials", if they do something interesting. Mostly because "New Material" sounds a lot more relevant to commercial application than "New Molecule". But is a molecule really a material? No, but when you have lots of molecules together that exhibit some neat property, that's a material. If that sounds confusing, it's because it is. As I said, the meaning of "material" has become very elastic. Also note that materials chemists can use inorganic (ceramics) or organic (plastics and polymers) materials. Of course, the FIRST materials chemists were plants and animals - I mean, what are the most basic materials if not biological membranes and plant fibers like cotton? Note that some animals use inorganic materials also - seashells, for instance, are composed primarily of calcium carbonate, an inorganic material, and let's not forget bones and teeth!

Anyway, most people seem to agree that materials are things in the solid state. And materials are usually subdivided into two categories: structural materials and electronic materials. Structural materials are best described as "stuff things are made of". Things like plastics, fibers, ceramics, glasses. While they seem boring, a lot of chemistry is involved in making stronger, lighter, more heat resistant structural materials. But, it's a whole separate area of chemistry than what I know. "Electronic materials" are best described as "stuff that does something". These are things like: semiconductors, superconductors, magnetic materials, etc. So, they're important. Also note that these two categories are not mutually exclusive. Especially today, many electronic materials can also have interesting structural applications, such as carbon nanotubes, conducting polymers, etc.

Nanomaterials (an even hotter word than materials) are basically the same as bulk materials but chopped up into very tiny (nanometer-scale) pieces. You might ask why that's interesting. Well it is because it turns out that when materials are made on a nanometer (molecular) scale, strange things start to happen. For instance, take a semiconductor (we'll talk about them later) in bulk. Basically, a big hunk of semiconducting material has a lot of useful, interesting properties. They can be made into all sort of useful things: solar cells, LEDs, transistors, lasers, etc., all use bulk semiconductors in some form for their function. However, an interesting thing is that when you take a semiconductor and break it up into small crystals that are several nanometer in diameter, you get this:



These are called semiconducting nanocrystals, or "Quantum Dots". What you see here are different colored luminescent solutions, and you might be surprised to know that they are all composed of the same semiconducting material (cadmium selenide). The only difference is how small the pieces of the bulk material are broken down into. Here they probably range from around 2 nm (blue dots) to 6 nm (red dots) in diameter. This is a purely quantum mechanical effect. They also do a lot of other weird things, but the point is that when you take bulk materials and cut them into tiny pieces, new properties emerge. While QDs are still a topic of intense investigation because their physics are not completely understood, they are already being developed for a lot of interesting applications, from lasers to biological sensors. This is because unlike a fluoresent molecule, which is typically prone to decomposition after long irradiation times, QDs are (in principle) very stable, and also it is not straightforward how to synthesize a molecule that fluoresces a particular color. For quantum dots, all you have to do is vary their size!

Anyway, quantum dots are what we'll work up to, but first we're going to have to go back and discuss bonding and atomic structure in a little more detail. Pretty much we'll pick up where we left off... at some point.

[Kalah]

Oh, look at all the pretty colours! Wheee...

Groovy, man.

[winterfate]

@Corribus: Cool!

I second what Kalah said about the colors!

I've learned some things about nanotechnology in General Chemistry. (carbon nanotubules, for example.)

You know...now that I mention that, there's a seminar here (at college; have no connection at home right now...so sorry in advance if I don't post much/frequently) today about nanotechnology.

Hmm...I think I'll go. Take care and thanks for the teaser!
Much appreciated!