Atoms

Sell it?!!! I'm not squeezed into the new place enough to force me to do that.However I do have a number of moderately good condition Mad magazines from the '55 to '57 time frame.Also, as hard as it is to contemplate, I'm going to pack up my complete (I hope) from issue 1 of Isaac Asimov's Science Fiction magazine and put it on Ebay.

Argh! Am I the only person who's never met a big-name scientist?

As far as colour goes, I believe you are correct. My understanding is that "colour" is a meaningless concept at the level of individual atoms, because they are smaller than the wavelengths of light that our eyes interpret as colour. So, if you want to get technical about it, nothing really has colour. What things have are specific properties that reflect the wavelengths of light that we perceive as colour.Now, whether or not these properties are inherent in individual atoms, I don't know. But even if they are, you won't see their "colour" until you have a large enough group of them to reflect the necessary light. In a sense, you might say that a large enough group of atoms has colour, but a single atom does not.Of course, I'm no expert. This is all half-remembered information from years ago. Somebody can correct me if anything I've said here is wrong.

Yukawa (an abysmally bad lecturer - he visited the physics dept I was working in -- it wasn't much more than a hello)
Samulson (economics -- just a short discussion after a talk)
Freeman Dyson (another discussion about SETI etc. His son lives near here)So does, btw, Spider Robinson whom I've spoken to a few times in our local Science Fiction book store.Gloat!
This message has been edited by NosyNed, 11-20-2004 04:12 PM

Yes, a single atom can send out light. Each atom (or molecule) has a certain configuration of electrons and thus can send out a specific configuration of light. I'm not sure if there are any instruments that are sensitive enough to pick up single photons, though.Atoms have colour in exactly the same way a painting do.

Heh, indeed.I'm starting to see a pattern here. You've met Richard Feynman, who is now dead. Brad has met Carl Sagan, who is now dead. Both of you stay the hell away from Stephen Hawking, you hear me?

Hi Melchior,Thanks for your reply. I'd just like to clarify a few things, if that's ok.As I understand it, when light encounters matter it gets scattered, with some frequencies being absorbed and others being reflected (depending on the properties of the matter in question), thereby determining what colour we see. Is this correct, so far? I always thought that individual atoms were too small to be detectable by any wavelength visible to humans. I'm sure I remember reading something to the effect of: "It would be like trying to take a photograph of a grain of sand by firing cannonballs at it." Something like that, anyway. It's possible, though, that what I read was about something completely different; it was years ago.I seem to recall that "photos" have been taken at the atomic level, using electrons instead of photons (I think it was electrons). Is this correct? Are there any true photographs of atoms (using actual visible light)? It doesn't have to be one single atom; just anything that shows actual atomic structure. If so, do you have a link? I'd love to see. Just to be sure I understand correctly, when you say that atoms "have" colour, do you simply mean that the material properties which cause a given element to reflect the light that my eyes interpret as a certain colour are contained within each of the element's individual atoms?Or are you saying that each of its individual atoms actually reflects light in exactly the same way as does the whole? That if we had an ordinary photographic camera, with an atomic-level magnification, the individual atoms would actually show up on the photographs as having colour? If so, would their colour be the same as that of the macroscopic whole (assuming, for the sake of argument, 100% purity of the element in the overall grouping)?

Id be interested in the MAD magazines if you would be selling those

Atoms all have a characteristic spectra consisting of one or more colours. When they absorb energy, the electrons in them get excited from one orbital to another, and the energy gap between orbitals is very well defined. When the electrons fall back down to their original orbital, they are forced to get rid of this extra energy. This is emitted as a photon, and because the energy difference in the orbitals is well defined, the energy of this photon is also well defined.This means that the colour of light that the atoms emit is totally characteristic of that particular atom, and can be used to detect what elements exist in stars etc. You were right that the width of an atom is much less than the wavelength of visible light though (measured best in angstroms rather than microns).

Correct, if you'll let me replace "detectable" with "able to be imaged." The gas in a neon light, for instance, emits photons at one per atom that we can see, so the atoms are "detectable" at our eyes' wavelengths.
There are "pictures" of atoms lined up in crystals and the like - these are made using atomic force microscopy or AFM. I know almost nothing about how it works, though http://stm2.nrl.navy.mil/how-afm/how-afm.html helped somewhat. I haven't Googled up anything yet that has both explanations and some good pictures, though. No, it's not that simple. Your cannonball analogy still applies, for one thing. And secondly, a piece of silver or copper looks the way it does mostly because of the "sea" of electrons that surround the individual atoms in the crystals. I read a little more detail on this 30 years ago, but that detail is gone, along with its source, from my brain. Now in the case of a colored gas or liquid - chlorine or bromine - I suspect that the color is intrinsic to the molecules - sets of just two atoms in these cases. These actually absorb certain wavelengths of light, leaving a color we can sense.

I believe that color is the electron making quantum leaps to and from higher and lower valance shells. The light emitted is electrons in a higher energy state. Thats why steel glows that beautiful color when heated, And also why elements emit they're prospective colors when 'excited'. edit to add...Humans perceive color by light that is reflected back to our retina. The wavelength that is not absorbed is the color we perceive. I think this is correct. This message has been edited by 1.61803, 11-21-2004 10:37 AMThis message has been edited by 1.61803, 11-21-2004 10:39 AM

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Just to be sure I understand correctly, when you say that atoms "have" colour, do you simply mean that the material properties which cause a given element to reflect the light that my eyes interpret as a certain colour are contained within each of the element's individual atoms?

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Or are you saying that each of its individual atoms actually reflects light in exactly the same way as does the whole? That if we had an ordinary photographic camera, with an atomic-level magnification, the individual atoms would actually show up on the photographs as having colour? If so, would their colour be the same as that of the macroscopic whole (assuming, for the sake of argument, 100% purity of the element in the overall grouping)?

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What gives an object a certain colour isn't reflection. It's absorption of certain frequencies of sunlight (or other energy, electrical lamps work) and the emitting of those towards any observer. This works ONLY on an atomic or molecular level, and if you have more of them, it just adds up the intensity.You are correct that reflection, and other similar phenomena like the usage of x-rays to examine crystalline structures, often (but not always) depend on more than one atom, but those are not what determines colour.

OK sorry I havent responded sooner but my question seemed unclear to me after i read it but what i really wanted to know is what is holding molecules together. like if I look at my arm at the skin cells, What is holding them together? The molecules to each other i mean. I read that some people said that it was electric charges or something but that doesnt seem strong enough to hold my skin together say i just barely bump into something. Anyone want to help clear this up for me thatd be great. Just looking for an answer. Basically I want to know whats keeping the molecules in our body from just separating and floating off.

Electrical forces - specifically the electron clouds around atoms, that are either shared between atoms or donated by one atom to another. It's about two chapters' worth of a beginning chemistry book - look for "ionic bonds", "covalent bonds", and "van der Walls bonds (or forces)".At 2000 degrees Celsius, all your molecules will indeed float off. Stay out of places that hot.

Ridiculous.......after all, this exchange of information should obviously be collapsing the wave function (right, Crash?)......therefore, molecules don't exist.