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Visual atomic physics

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Indi
There have been a couple of really awesome developments in atomic physics the last couple of weeks that have gone unmentioned here. Most of these developments are more cool than groundbreaking, and mostly about making long-held physics theories visual.

The first is an image taken of a single pentacene molecule - which is a molecule made up of five linked benzene rings. It is the first image taken of a single molecule (we have imaged atoms before, both by themselves and in crystalline structures, but never molecules because they are so fragile). You can clearly see the benzene ring structures, and the carbon-carbon bonds in the benzene rings, and if you squint you can even make out the hydrogen atoms on the periphery (they're the smudges that extend away from the outside vertices of the hexagons).



(source: http://news.bbc.co.uk/2/hi/science/nature/8225491.stm)

The second is an image of a single atom, but such a clear image that you can actually make out the individual electron orbitals. In this image, you can see the 1s and 2p orbitals as blue clouds. This is a neat way to show that quantum mechanics is probably right.



(source: http://insidescience.org/research/first_detailed_photos_of_atoms)
ninjakannon
This is amazing, I had no idea we had such precise methods of imaging!

I don't fully understand the explanation given for the generation of the second image, the electron orbitals.

Specifically, I do not see that this:
Quote:
The soft blue spheres and split clouds seen in the images show two arrangements of the electrons in their orbitals in a carbon atom. The structures verify illustrations seen in thousands of chemistry books because they match established quantum mechanical predictions.


is verified by this:
Quote:
The atom at the tip of the chain emitted electrons onto a surrounding phosphor screen, rendering an image of the electron cloud around the nucleus.


If an electron was a point, but a moving point, then it would be emitted from a certain location; if there are enough electrons, they would be emitted from different locations, thus giving the appearance of an orbital. I hope this explanation suffices.

Obviously, I don't understand something here, so what is it?
Indi
ninjakannon wrote:
This is amazing, I had no idea we had such precise methods of imaging!

Oh yes. i'm a big fan of imaging the very, very small. This is an image of the surface of a silicon crystal, cleaved across the {111} plane. The "balls" you see are the silicon atoms, and you can clearly see the hexagonal structure from cleaving the diamond cubic crystal across the {111} plane. You can even see where there are imperfections in the crystal structure!


ninjakannon wrote:
I don't fully understand the explanation given for the generation of the second image, the electron orbitals.

Both images are images of electron orbitals - the first image is an image of the 1s orbital, the second is an image of one of the three 2p orbitals.

ninjakannon wrote:
Specifically, I do not see that this:
Quote:
The soft blue spheres and split clouds seen in the images show two arrangements of the electrons in their orbitals in a carbon atom. The structures verify illustrations seen in thousands of chemistry books because they match established quantum mechanical predictions.


is verified by this:
Quote:
The atom at the tip of the chain emitted electrons onto a surrounding phosphor screen, rendering an image of the electron cloud around the nucleus.


If an electron was a point, but a moving point, then it would be emitted from a certain location; if there are enough electrons, they would be emitted from different locations, thus giving the appearance of an orbital. I hope this explanation suffices.

Obviously, I don't understand something here, so what is it?

Well, the paper hasn't been published yet - all we have is the very brief article that is rather vague about the process. But from what i understand (and some of this is guess work):

They set up a potential of hundreds of volts across the atom at the tip. A charge (like an electron), given a potential, acquires energy. That energy causes the electron to break free of the atom and fly off in a random direction. The atom quickly picks up another electron from the electric field set up by the potential, and the process repeats over and over. The atom keeps reacquiring electrons, then firing them off.

They put a filter to allow only electrons travelling in a certain direction, and a screen to record the emitted electrons. Over time, thousands of electrons were recorded, and the patterns are what you see. i suspect they select which orbital to image by changing either the potential field strength, or the temperature of the sample.

So in other words, you can think of it like one electron emitted over and over and over. Each time it gets emitted, it is at a different position in the orbital. Over time, we get the cloud image.
Voodoocat
Unbelievable! The top picture clearly shows the sharing of pi electrons, and the bottom! Wow! It's one thing to see the probability density drawings of orbitals, but to actually see them Razz

Thanks for the posting!!!!!
Roflcopter
[quote="Indi"]
ninjakannon wrote:
This is amazing, I had no idea we had such precise methods of imaging!

Oh yes. i'm a big fan of imaging the very, very small. This is an image of the surface of a silicon crystal, cleaved across the {111} plane. The "balls" you see are the silicon atoms, and you can clearly see the hexagonal structure from cleaving the diamond cubic crystal across the {111} plane. You can even see where there are imperfections in the crystal structure!


ninjakannon wrote:
I don't fully understand the explanation given for the generation of the second image, the electron orbitals.

Both images are images of electron orbitals - the first image is an image of the 1s orbital, the second is an image of one of the three 2p orbitals.

ninjakannon wrote:
Specifically, I do not see that this:
Quote:
The soft blue spheres and split clouds seen in the images show two arrangements of the electrons in their orbitals in a carbon atom. The structures verify illustrations seen in thousands of chemistry books because they match established quantum mechanical predictions.


is verified by this:
Quote:
The atom at the tip of the chain emitted electrons onto a surrounding phosphor screen, rendering an image of the electron cloud around the nucleus.


If an electron was a point, but a moving point, then it would be emitted from a certain location; if there are enough electrons, they would be emitted from different locations, thus giving the appearance of an orbital. I hope this explanation suffices.

Obviously, I don't understand something here, so what is it?

Well, the paper hasn't been published yet - all we have is the very brief article that is rather vague about the process. But from what i understand (and some of this is guess work):

They set up a potential of hundreds of volts across the atom at the tip. A charge (like an electron), given a potential, acquires energy. That energy causes the electron to break free of the atom and fly off in a random direction. The atom quickly picks up another electron from the electric field set up by the potential, and the process repeats over and over. The atom keeps reacquiring electrons, then firing them off.

They put a filter to allow only electrons travelling in a certain direction, and a screen to record the emitted electrons. Over time, thousands of electrons were recorded, and the patterns are what you see. i suspect they select which orbital to image by changing either the potential field strength, or the temperature of the sample.

So in other words, you can think of it like one electron emitted over and over and over. Each time it gets emitted, it is at a different position in the orbital. Over time, we get the cloud image.[/quote

wow i could never get this stuff if i tried to learn it looks like a very hard topic to study Surprised
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