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12-22-2002, 11:50 AM
#466
Goldfish
Originally posted by russ_watters
Why? the change in your pocket doesn't end up as a solid mass of metal, does it? Metal objects need to be chemically bonded together to become one object (a weld is chemical bonds).
No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).
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12-22-2002, 10:06 PM
#467
No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).
A brand new penny has very little oxidation and air doesn't make any difference since there will always be places where there is no air between the pennies (otherwise they woudln't jingle). And yes, the bonds are easy to form, but not so easy that they form sponatneously. They need a push - force or heat.
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12-22-2002, 11:11 PM
#468
OK, you seem to be saying that all solids are held together by chemical bonds, right? That would explain it, but I guess I don't see why that is. Is it somehow related to that "heat of fusion" stuff? Wait, nevermind..that is going the wrong way. (takes heat to *melt* it, so it gives off heat when it freezes)
I was under the impression that the only difference between solids and liquids was that liquid molecules had enough energy to freely move past one another, and solids do not. But the intermolecular forces involved would be exactly the same.
Anyway, that's what's going on in my mind. Am I making myself look like an idiot?
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12-22-2002, 11:50 PM
#469
Great White Shark
Originally posted by pcchen
No, I was talking about pure metals (without oxide or other things on the surface) in a vaccum chamber. Since the metal atoms can form bonds easily, I think it is possible for two metal objects to become one under room temperature. It is much easier under high temperature (that's how we weld metals).
I don’t believe the atoms at the surface would just “sit” in a state ready to fuse with another piece of metal even in a vacuum where there would be no way of oxidization, etc on the surface. The surface atoms would not have a complete complement of electrons in their outer shell, this is just about the least favorite state there could be, so I’m certain they would find a way to complete their shell. Once this occurred, there would be an energy barrier to overcome before the two pieces fused as you suggest. Gravity alone would not be able to overcome this.
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12-23-2002, 01:15 AM
#470
Goldfish
No, I don't know what happens if you just put two objects together. However, I believe that you don't need too much force to make two metal objects to become one. Some information about "cold welding" may be interesting (although I can't find much on google). However, cole welding works only on some types of metal...
Last edited by pcchen; 12-23-2002 at 01:19 AM.
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12-23-2002, 01:56 AM
#471
Catfish
Originally posted by Strogian
Two separated liquids of the same material will combine without any chemical bonds, right? So what makes solids different? Take water for example. If you take two ice cubes and put them together, they don't bond. But if you melt them down (just a layer of liquid on the surface may suffice) and refreeze them, they've become a single object. There aren't any chemical reactions going on there, right? What was preventing them from bonding when solid?
Actually chemical bonds do occur. The bonds between water molecules are called hydrogen bonds. Because the oxygen molecule is more electronegative (wants electrons really bad) compared to hydrogen the oxygen atom actually starts to draw hydrogens' electrons closer to itself. This causes oxygen to be slightly negatively charged and hydrogen slightly positively charged. Because H20 molecules have this small charge they actually bond to each other (hydrogen atom to an oxygen atom of another molecule and vice versa.) This is why water forms droplets. *edit* my ASCII diagrams didn't format correctly so you might want to do a search for hydrogen bonding in google to get some nice pictures.
Ice forms when these water is frozen into a crystal lattice; the molecules align themselves with their neighbors so that the oxygen of one molecule is near a hydrogen of another. When this happens the molecules actually spread out. This is why ice floats on water, not because there are air bubbles in the ice. Two ice blocks don't bond togeather because their crystal lattices have not made any connections.
Hydrogen bonding occurs when hydrogen is bound to highly electronegative atoms such as nitrogen, fluorine, and oxygen. This is not the only type of bonding that occurs between molecules. There is something called London Dispersion Forces, too. I won't get into that but you can do a search for Intermolecular Forces (IMFs) in google to learn more and get diagrams which will explain a whole lot.
Last edited by mozilla4; 12-23-2002 at 01:58 AM.
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12-23-2002, 09:04 AM
#472
Originally posted by mozilla4
Actually chemical bonds do occur. The bonds between water molecules are called hydrogen bonds. Because the oxygen molecule is more electronegative (wants electrons really bad) compared to hydrogen the oxygen atom actually starts to draw hydrogens' electrons closer to itself. This causes oxygen to be slightly negatively charged and hydrogen slightly positively charged. Because H20 molecules have this small charge they actually bond to each other (hydrogen atom to an oxygen atom of another molecule and vice versa.) This is why water forms droplets. *edit* my ASCII diagrams didn't format correctly so you might want to do a search for hydrogen bonding in google to get some nice pictures.
What do you do for living mozilaa? I am just wondering you have all this chemistry knowledge for business or pleasure?
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12-23-2002, 09:12 PM
#473
Catfish
Originally posted by Prince
What do you do for living mozilaa? I am just wondering you have all this chemistry knowledge for business or pleasure?
I do chemistry research for business. I work for Smith's Chemistry Corporation a wholly owned subsidiary of The College Board.
Desktop: Asus P4T533-c | Pentium 4 2.4B | Kingston 256 Mb PC1066 RDRAM | ATi Radeon 9800 Pro 128MB | Creative Audigy w/ 1394 | Western Digital 100GB Special Edition | HP CD-Writer 9500 | Toshiba DVD-ROM | Antec SX635 Case w/ 380Watt PSU | Viewsonic VX900 19" LCD
Laptop: Compaq Evo N800w | Pentium 4 Mobile 2.2 GHz | ATI Fire GL 9000 Mobility w/ 64 MB RAM | 15" 1600x1200 LCD | 512 MB RAM | 60 GB 5400 RPM Hard Drive | 24x/10x/24x/8x DVD/CD-RW
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01-21-2003, 11:10 PM
#474
Just thought of another question, regarding the speed of light. (what this topic was originally about, I think ) If the speed of light is measured in a vacuum, I know that it is always measured to be c, regardless of the velocity of the measuring platform. But, if it is measured in some other medium (air, glass, etc.), will the measurement depend on, say, the velocity of the medium? (i.e. if it is windy, will you measure light to be moving more quickly in the direction of the wind?) Or is it still measured as a constant, just less than c?
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01-22-2003, 12:12 AM
#475
Great White Shark
Light will travel slower in other mediums, but never faster then it travels in a vacuum. The speed is still not dependant on the motion of the underlying medium.
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01-22-2003, 01:35 PM
#476
Goldfish
Hmm... what if some winds change the density of air? Doesn't light travel slower in more dense air?
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