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Author Topic:   Atoms
NosyNed
Member
Posts: 9011
From: Canada
Joined: 04-04-2003


Message 16 of 80 (161881)
11-20-2004 3:51 PM
Reply to: Message 15 by sidelined
11-20-2004 2:57 PM


Re: Feynman
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.

This message is a reply to:
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Replies to this message:
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Tony650
Member (Idle past 4280 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 17 of 80 (161883)
11-20-2004 3:56 PM
Reply to: Message 10 by NosyNed
11-18-2004 9:45 PM


Re: Feynman
NosyNed writes:
I have Feynman's autograph on his "Character of Physical Law". He spoke here about 20 years ago.
Argh! Am I the only person who's never met a big-name scientist?

This message is a reply to:
 Message 10 by NosyNed, posted 11-18-2004 9:45 PM NosyNed has replied

Replies to this message:
 Message 19 by NosyNed, posted 11-20-2004 4:11 PM Tony650 has replied

  
Tony650
Member (Idle past 4280 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 18 of 80 (161884)
11-20-2004 4:06 PM
Reply to: Message 12 by Spencer
11-20-2004 2:18 PM


Spencer writes:
Is it true that atoms are tasteless, colorless and odorless?
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.

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Replies to this message:
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NosyNed
Member
Posts: 9011
From: Canada
Joined: 04-04-2003


Message 19 of 80 (161885)
11-20-2004 4:11 PM
Reply to: Message 17 by Tony650
11-20-2004 3:56 PM


Others
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

This message is a reply to:
 Message 17 by Tony650, posted 11-20-2004 3:56 PM Tony650 has replied

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Melchior
Inactive Member


Message 20 of 80 (161935)
11-20-2004 7:00 PM
Reply to: Message 18 by Tony650
11-20-2004 4:06 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.

This message is a reply to:
 Message 18 by Tony650, posted 11-20-2004 4:06 PM Tony650 has replied

Replies to this message:
 Message 22 by Tony650, posted 11-21-2004 6:02 AM Melchior has replied

  
Tony650
Member (Idle past 4280 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 21 of 80 (162003)
11-21-2004 5:53 AM
Reply to: Message 19 by NosyNed
11-20-2004 4:11 PM


Re: Others
NosyNed writes:
Gloat!
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?

This message is a reply to:
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Tony650
Member (Idle past 4280 days)
Posts: 450
From: Australia
Joined: 01-30-2004


Message 22 of 80 (162004)
11-21-2004 6:02 AM
Reply to: Message 20 by Melchior
11-20-2004 7:00 PM


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?
Melchior writes:
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.
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.
Melchior writes:
Atoms have colour in exactly the same way a painting do.
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)?

This message is a reply to:
 Message 20 by Melchior, posted 11-20-2004 7:00 PM Melchior has replied

Replies to this message:
 Message 24 by happy_atheist, posted 11-21-2004 8:46 AM Tony650 has replied
 Message 25 by Coragyps, posted 11-21-2004 9:58 AM Tony650 has replied
 Message 27 by Melchior, posted 11-21-2004 10:53 AM Tony650 has replied

  
Yaro
Member (Idle past 6744 days)
Posts: 1797
Joined: 07-12-2003


Message 23 of 80 (162005)
11-21-2004 6:12 AM
Reply to: Message 16 by NosyNed
11-20-2004 3:51 PM


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

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happy_atheist
Member (Idle past 5161 days)
Posts: 326
Joined: 08-21-2004


Message 24 of 80 (162013)
11-21-2004 8:46 AM
Reply to: Message 22 by Tony650
11-21-2004 6:02 AM


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).

This message is a reply to:
 Message 22 by Tony650, posted 11-21-2004 6:02 AM Tony650 has replied

Replies to this message:
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Coragyps
Member (Idle past 982 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 25 of 80 (162018)
11-21-2004 9:58 AM
Reply to: Message 22 by Tony650
11-21-2004 6:02 AM


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."
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.
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?
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.

This message is a reply to:
 Message 22 by Tony650, posted 11-21-2004 6:02 AM Tony650 has replied

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1.61803
Member (Idle past 1752 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 26 of 80 (162024)
11-21-2004 10:35 AM


leap of faith or quantum leap?
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 AM
This message has been edited by 1.61803, 11-21-2004 10:39 AM

  
Melchior
Inactive Member


Message 27 of 80 (162030)
11-21-2004 10:53 AM
Reply to: Message 22 by Tony650
11-21-2004 6:02 AM


quote:
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)?
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.

This message is a reply to:
 Message 22 by Tony650, posted 11-21-2004 6:02 AM Tony650 has replied

Replies to this message:
 Message 53 by Tony650, posted 11-24-2004 4:00 PM Melchior has replied

  
jacketsfan4life
Inactive Member


Message 28 of 80 (162072)
11-21-2004 2:11 PM


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.

Replies to this message:
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Coragyps
Member (Idle past 982 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 29 of 80 (162075)
11-21-2004 2:18 PM
Reply to: Message 28 by jacketsfan4life
11-21-2004 2:11 PM


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.

This message is a reply to:
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JasonChin 
Inactive Member


Message 30 of 80 (162222)
11-22-2004 3:32 AM
Reply to: Message 5 by NosyNed
11-18-2004 7:36 PM


Re: Holding atoms together
It is the electromagnetic force mediated by photons being exchanged that holds molecules together.
Ridiculous.......after all, this exchange of information should obviously be collapsing the wave function (right, Crash?)......therefore, molecules don't exist.

This message is a reply to:
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