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turd
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| Quote: | | We did a q-dots lab in my pChem class some time back. We made black, blue, and red gold solutions. This was due to the size of the gold clusters
being comparable to the wavelength of the photons or something of that nature. |
These clusters are typically in the range of 1-100nm, far below the wavelength of visible light.
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12AX7
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AFAIK, metallic color in terms of steel gray to bluish zinc (it really does look kinda bluish, come to remember it) is usually the surface oxide at
work.
Hmm, now I need to know zinc's absorbtion spectrum...
Tim
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unionised
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There's a gold indium alloy that's really blue, not an oxide film.
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pyrochem
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Earlier in this thread, it was mentioned that gold and copper absorb the wavelengths they do not reflect. It seems like some of the light is
transmitted. Hold a bright light behind a piece of gold leaf and the transmitted light will look blue/green. I think the same effect occurs with
thin films of copper. Is the light really transmitted or is this the same effect as with the quantum dots?
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Jdurg
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Cesium metal is also a yellow color just like gold, and osmium metal has a blue hue to it. Pure bismuth and pure tantalum metal have a pinkish color
to them as well. Still, Copper, Gold and Cesium are the only three metals I know of that have a solid color to it and not a hue.
\"A real fart is beefy, has a density greater than or equal to the air surrounding it, consists of the unmistakable scent of broccoli, and usually
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neutrino
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Is osmium really blue or is this just refraction from its oxide layer? A quick google search revealed no answers.
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Nerro
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According to my professors the high mass of the nuclei near and past gold causes relativistic contraction of the s and p orbitals and relativistic
expansion of the d and f orbitals. This accounts for the chemically inert nature of Au, Pt, Hg and other elements, incidentally it also accounts for
the fact that Hg is a liquid at RT. It would seem to me that it also explains why lanthanides and actinided quite readily go to very high oxidation
states like +6 and +8.
The colour of gold, caesium and some other elements is said to be caused by the decreased energy requirement of the jump from 5d to 6s which is caused
by this relativistic contraction.
Why the s and p orbitals contract as the mass of the electrons increases I don't know. The same goes for the relativistc expansions. Just like I'm not
sure why the speed of electrons should vary according to their distance from the core.
-edit- I did some reading and apparently the electrons move in circles within their "probability clouds", as their masses increase because their
speeds do (I'm still fairly clueless why the speeds would vary...) the radii of these circles decrease and are thus brought closer towards the core.
It's the center of the electrons orbit that is used to calculate the properties of the particular electrons and so if the radius of the orbit
decreases so does the observed distance to the nucleus. The weird shapes of the probability clouds for d and f electrons might account for their
expanding rather than contracting.
This whole story makes a lot of sense to me except for one thing, why does the speed of an electron increase as it goes farther away from the nucleus?
[Edited on Mon/Jul/2006 by Nerro]
#261501 +(11351)- [X]
the \"bishop\" came to our church today
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turd
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| Quote: | | It would seem to me that it also explains why lanthanides and actinided quite readily go to very high oxidation states like +6 and +8.
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No, this is mostly non-relativistic effect: higher energy orbitals are more easily oxidised/polarised. You see the same effect for all groups:
Xe-compounds, but no He-compounds. I easily oxidised, F not so. Etc, etc...
| Quote: | | Why the s and p orbitals contract as the mass of the electrons increases I don't know. |
Gravitation.
| Quote: | | The same goes for the relativistc expansions. |
If the inner orbitals are contracted, the nucleus is shielded, therefore the electric field is weakened.
| Quote: | | Just like I'm not sure why the speed of electrons should vary according to their distance from the core. |
Electric and gravitational field diminish with distance.
| Quote: | | The weird shapes of the probability clouds for d and f electrons might account for their expanding rather than contracting. |
Kind of; it's not so much the shape as the radial probability distribution.
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Nerro
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| Quote: |
Electric and gravitational field diminish with distance. |
Why does that make the electrons travel
faster when they go farther from the core? Also, I thought gravitational pull was insignificant at the atomic level. Electrostatic
force is supposed to be something like 10^27 times stronger...
#261501 +(11351)- [X]
the \"bishop\" came to our church today
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Jdurg
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| Quote: | Originally posted by neutrino
Is osmium really blue or is this just refraction from its oxide layer? A quick google search revealed no answers. |
Osmium only forms the simple tetroxide (OsO4) under typical conditions, and this is a VERY volatile and very nasty smelling liquid. As a result, it
does not bond at all to the metal itself. Osmium metal itself is a nice bluish color and is really neat to see.
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praseodym
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something like this?
Alles sollte so einfach wie möglich gemacht werden aber nicht einfacher.
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woelen
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Just a few remarks about the past few posts in this thread.
Lanthanides do not form high-oxidation state compounds. The highest oxidation state, which can be achieved is +4 for cerium metal (and from experience
I know that this is DIFFICULT to obtain from the +3 ion). The lanthanides' main feature is that they are so uniformly restricted to their +3 oxidation
state. Some exist in +2 (but with great difficulty) and cerium as +4, and that's all.
Osmium does not only form OsO4. It also forms a lower, very hard, inert and high melting point oxide, OsO2. But I agree with Jdurg, that osmium has a
blue hue and I also think it is due to the color of the metal itself, and not due to oxide layers.
Gravity does not play ANY role at the chemistry at the atomic level. Gravity only plays an important role at super-macro scale (e.g. planets, moons,
solar systems), even two bodies of 100 kg, held close together have extremely low gravitational interaction. Even the slightest static charge on these
bodies will result in a larger electrolstatic force.
The relativistic contraction of orbitals in the heavier elements is not due to high mass of the nucleus, but due to high charge of the nucleus. If you
solve the wave equation for a two point-charge system, and you increase the charge of one of them, then you'll see that the orbitals shrink and
"velocity" increases. It is this increase of "velocity" which introduces relativistic effects. For large charges of the nucleaus, one should solve the
wave equations, but not in a classical sense, but in a relativistic sense. The math involved, however, is increadibly complex.
[Edited on 12-7-06 by woelen]
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turd
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Ugh. Of course gravity doesn't play a role, what was I thinking!
| Quote: | | The relativistic contraction of orbitals in the heavier elements is not due to high mass of the nucleus, but due to high charge of the nucleus. If you
solve the wave equation for a two point-charge system, and you increase the charge of one of them, then you'll see that the orbitals shrink and
"velocity" increases. It is this increase of "velocity" which introduces relativistic effects. For large charges of the nucleaus, one should solve the
wave equations, but not in a classical sense, but in a relativistic sense. The math involved, however, is increadibly complex. |
For qualitative statements you don't necessarily have to solve the Dirac equation and not even the Schrödinger equation. It's still the same laws of
nature you find on a macroscopic scale, just applied in a "funny" way. Isn't it as simple as more mass and same force gives less speed and thus a
smaller orbital?
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DrP
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| Quote: |
Quote: BROMIC
We did a q-dots lab in my pChem class some time back. We made black, blue, and red gold solutions. This was due to the size of the gold clusters being
comparable to the wavelength of the photons or something of that nature.
Quote TURD
These clusters are typically in the range of 1-100nm, far below the wavelength of visible light.
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I think that it comes into the wavelenght of the surface plasmons though. In Raman Spectroscopy, if your metal clusters are the right size (depending
on the sample and the laser wavethength) you can get the surface plasmons to resonate which enhances your Raman scattering about 50 fold. Usefull for
very weak/faint signals.
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Nerro
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I always thought the colour of a colloid had something to do with the way light is diffracted inequally by the particles. The perceived colour would
be the product of the bending of the light.
Can someone explain to me what plasmons are?
-edit- google really is a good friend sometimes 
I read that plasmons are the colelctive oscillations of the "electron" gas in a plasma. I can see how the valence electrons of a metal can move about
freely enough to enable similar effects on its surface. Can these collective electron-cluster oscillations also absorb and emit photons?
The coolness of theoretical chemistry never really wears off, does it? 
[Edited on Fri/Jul/2006 by Nerro]
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the \"bishop\" came to our church today
he was a fucken impostor
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DrP
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| Quote: | [quote: Nerro]
I read that plasmons are the colelctive oscillations of the "electron" gas in a plasma. I can see how the valence electrons of a metal can move about
freely enough to enable similar effects on its surface. Can these collective electron-cluster oscillations also absorb and emit photons?
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Thats right - SURFACE plasmons. I don't actually know if the photons are absorbed and re-emmited by the surface plasmons, but, it would make sense -
if the Raman scattering is increased 50 fold (it is at least 50 fold - I can't remember the exact amplification factor) and the plasmons are in
resonance then I could well imagine that a photon of the right wavelength could get absorbed and then thrown out again at right angles (Raman
scattered light is given of at 90 deg).
| Quote: |
The coolness of theoretical chemistry never really wears off, does it?
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Ha Ha - I might agree, but alot of people would call you a complete geek!  As for it being theoretical - a friend of mine done his Ph.D. back in the 90's on
Raman spectroscopy and the effect of surface plasmon resonances on the signal. The work was being undertaken with a view to being used for drug
delivery mesurements - diffusion co-efficients were mesured across membranes using Raman spec as the detection system for extreamly small
concentrations of the drug. Because the drug concs were so low - they were trying to use the surface plasmon resonances from coloidal films to
amplify the signal. I thought it was all pretty cool as well.
Oops! sorry - I've just realised this is all abit off topic - although as it has been said the particle size of the clusters effect colour.
[Edited on 14-7-2006 by DrP]
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