Curious about the structure of a molecule, I went to wikipedia for basic information.
Pretty interesting, but I couldn’t find the answer to my basic queation, which is:
What would a molecule look like if you could pull one out and expand it to a visible size?
Also, can one molecule of a substance exist by itself? Can there be one lead (Pb, eh?) molecule floating around all by it’s lonesome?
Peace,
mangeorge
Unfortunately by expanding it to visible size, you are fundamentally changing how a the constituents of a molecule behave. What you see all molecular models is a probability distribution, and that distribution is governed by quantum mechanics.
Sure a molecule can exist by itself (for the most part depending on how exact “by itself” means).
C’mon, the question isn’t “could it exist”, but "what would it look like. Zoom in on that rascal with a video camera. Show it on your 52. 
One of the space-filling models is the sort of the best approximate representation, but there is no real answer - most of the molecule is empty space, and (assuming you could see the electrons and nuclei) it changes shape with time - bonds flex and vibrate, and the electron orbits expand and contract as the bond gets excited by radiation and then emits radiation. Each bond and atom will glow somewhat - maybe visibly, but probably not - bond excitation energies are often infra-red (at least for carbon chain compounds). So it will be fuzzy, averaging to something that looks like the Space-filling model.
But there really is no answer. One of the big fields in biochemistry is protein structure analysis - we know what the chemical makeup is, but we don’t know how the protein actually folds itself to a minimal energy configuration (let alone an activated configuration to accomplish something). Attempting to analyse this sort of thing required distributed computing (thus folding@home, a co-operative network of computers running a screensaver analysing protein folding patterns).
You do get single molecules - the air you breath consists of molecules of Oxygen (O[sub]2[/sub]) and Nitrogen (N[sub]2[/sub]), as well as a few other things (CO[sub]2[/sub] included). Some atoms (Helium, Argon, Neon, Radon) do not form molecules, they will exist as single atoms. Metals (like Lead) do not form molecules as such either. They can be vapourised into single atoms (by heat), but form metals (collections of atoms, possibly structured, generally sharing electrons over the whole mass) when they condense. However, a Boron-Boron bond has apparently been recently identified, giving B[sub]2[/sub] in an ionic structure with B[sub]12[/sub](Boron is a metalloid).
Si
It would be simultaneously invisible and pink.
Seriously, how is one supposed to say how something that cannot exist would look?
Mangeorge wants an answer to a question that is easy to ask and at first sounds like a legitimate question, or at least a plausible one.
Chronos is right - it’s an invisible pink color. Moreover, it has a shape kind of like disenfranchisement, long like a repair, bent in the middle like an idiom.
But there is at least a little more that we could say.
It is interesting to consider two important radii for an atom. One is the radius such that two atoms that have bonded together have their centers as far apart as the sum of these radii. In other words, it’s the radius you would use to draw spheres for the atoms, if you wanted atoms that are bonded together to just touch at their surfaces. This is a little weak, because the radius of a particular kind of atom would be somewhat different when it was next to different other kinds of atoms. In other words, there isn’t a single distance for each atom such that all their mutual separations match. But I think this is useable to a few percent.
The other kind of radius is the van der Waals radius, which is the radius such that atoms that are not bound to one another start pushing back when you try to crowd them into this distance. So, if you want to draw atoms as spheres and see them crowding, given that they are not bonded, you’d use this radius. This is always bigger than the first one. My impression is, maybe twice as big, roughly. But I think it’s also a bit weak.
There is a concept of stearic hinderance, that describes how parts of a molecule interfere with one another and don’t let the molecule take on certain shapes. The point of this is that all the surface atoms have van der Waals radii describing repulsion bumpers of a sort, and you can’t easily have these things intercept each other’s space. Similarly, a chain cannot take on certain shapes because multiple parts of the chain would have to be in the same place. Or, similarly, if you have your elbow bent at 90 degrees and your upper arm hanging down parallel to your spine, you have to have your forearm and hand in front of your trunk or behind it, and you can’t move between these positions without changing your elbow angle or upper arm orientation, because your hand can’t pass through your body.
I think all of these things are useful in picturing molecules and their activities. Moreover, the temptation to try to think of what a molecule looks like is just awful to resist. I think any good introductory chemistry text would have to make the point that molecules don’t have a visual appearance because the very idea of an appearance falls apart at such small sizes; and yet I know these texts are all going to draw molecules anyway.
Ah, well - most of them also seem to describe electrons circling around nuclei, last time I looked…
I’m not asking about god, just a simple molecule. The methane molecule in the linked article would be a good example.
But, those are atoms! Sister Mary Lawrence told me so.
Wah!
Einstein wouldn’t have treated me like this.
It’s not an impossible task. You need to specify what you’re going to model, though. For example, model an electron, or the nucleus, as occupying the most likely volume where it has a, say, 90 percent chance of being. This is often done for showing individual electron orbitals. For a molecule, you may want to only include the valance electrons (shown semi-transparent), since those are the ones involved in bonding, and the nucleus (maybe enlarged so you can see it).
Here’s a site, and another, that show visualizations of molecules. I don’t think either matches what I suggest above.
That is not the same as what a molecule looks like. That is just the probability function for the location of the electron.
There are ways of looking at molecules direcly. You can’t get close enough to see the individual atoms, but you can certainly make out individual molecules. On the other hand, these aren’t actually “looking” at molecules with your eyes. A Transmition Electron Microscope can get really close to looking at individual atoms. Mostly what you see is pi-clouds. Sigma bonds are pretty close to invisible. There is no real distinction between one atom and the next. In fact, the bonds between the atoms can actually be more visible than the atoms themselves.
Come to think of it, there is a meaningful answer to the OP’s question in many cases, though it’s probably not what he’s thinking of. Some molecules are already macroscopic size, so if you want to know what any of them looks like, you can just look at one and see. All good-quality crystals are single molecules, as are many plastic objects (depending on the type of plastic).
It is my interpretation of what mangeorge is asking for. In the OP, he says he’s curious about the structure of a molecule. When he asks what a molecule “looks like”, I believe he’s asking about the structure of a molecule and its electrons.
Yes, you can get an interperetation of the way a molecule is shaped this way. It has nothing to do with what color it is. Maybe you could fugure out a color, but I’m not sure. Woud different areas be colored differently?
I work at the research facility for a huge multi-national oil company. We have labs inhabited by a few scientists, lotsa chemists, and a mob of lab rats. They like to display these models, and they are the stick-and-ball variety shown in the linked article.
That’s what spurred my curiosity.
Chemistry people are an odd lot. I asked one of them what that is, and she said “it’s a molecule”. I then asked “is that what one actually looks like?” and she had a giggle fit.
Sounds familiar, doesn’t it. Maybe she thinks I’m cute. :dubious: She sure is.
Exactly.
:rolleyes: The OP said nothing about color. Nor did I. That was Chronos. I mentioned showing the electrons semi-transparent, but that was only so you could see where the nuclei were.
The stick and ball model is what a molecule looks like in roughly the same sense as a stick figure is what a person looks like. It just shows where the atoms are in relation to each other, and which ones are bonded with each other.
According to Feynman it would require magnifying a quarter inch drop of water till it was three thousand eight hundred miles in diameter before you could see an actual molecule.
That is, of course, if you could actually see a molecule, which, of course, you can’t. But it does give some idea of how small one of these suckers is.
http://www.energyandmatter.com/pages/physics/matter/feynmanexcerpt1.html
ZenBeam It’s nice to see you back.
Light is too corse a tool to depict the structure of a single molecule - things that are smaller than half the wavelength of a lightwave cannot be depicted. Visible light has wavelengths between 400 and 700 nanometers (4-710e-7 m), while the distance between two atoms in a molecule is in the order of 0.1 nanometer (1-310e-10 m). With x-rays, which have a much shorter wavelength, one can probe the shape of molecules. By scattering x-rays on crystals of a substance, one can determine the shape of even very complex molecules, such as proteins. From the scattering pattern, one can deduce the distribution of electrons in space. These electron densitities are the most direct atomar resolution depiction of a molecule we can make. However, there is no clear-cut “surface” of the atoms in the molecule, instead, the electron density just weakens as the distance to the atoms increases. In the pictures shown in the link above, points of equal electron density were connected to show the shape of the molecule, in the same way as points of equal altitude are connected by lines in a topological map.
These electron density maps are then used to determine the center of the atoms and fit a more abstract “atom and bond” model of the molecule.
This model can be used to produce the different kind of depiction of molecular structure you can find in various textbooks: The Van der Waals-surface depicts the atoms as spheres whose radii show how close a non-bonded atom could get, while the solvent accessible surface shows how close a solvent molecule can get to the atoms of the depicted molecule. Stick-an-Ball-models are more of an abstraction and emphasize which pairs of atoms share electrons in covalent bonds. For very complex molecules, we use even more abstract representations, emphasizing the way chain-shaped molecules protein chains fold to form the complex shapes that determine their function: Cartoon-models and ribbon models.
I read some years ago about a trick that makes individual atoms, and even isolated electrons visible. You hold the thing in a magnetic “Penning trap”, and shine a laser on it. Seen with a small telescope mirror, it’s a point of light. Not much practical use, but cool I thought.
It probably is stretching the definition of visible. I don’t know specifically what you are talking about, but single molecule detection is definitely well known. Another way to get a look at individual atoms is with atomic force microscopy. In reality though, what you are doing is “feeling” the atoms with a probe. They have a pretty nice picture of sodium chloride on that wiki.
Technically this is true, but of course the only reason this works is because you have a large repeating unit. You aren’t really looking at individual molecules. Also, you can’t really see protons with x-ray crystallography. Usually the position of the proton is just guessed at by the crystallographer. Neutron scattering can pick out protons. Structures of complex molecules such as protiens have additional difficulties in that they rarely crystalize out in the same form they are in solution.
It is possible to detect single photons emitted from a fluorescent molecule, and even detect spectral changes resulting from conformation changes in a molecule. You can use this to observe the folding and unfolding of individual proteins molecules. Light just does not have the spacial resolution to depict the shape of a molecule.
Atomic force microscopy can show individual atom. However, this is more like the sense of touch than sight. It can also be used to directly measure the binding forces between two individual molecules, e.g., between an antibody and an antigen