Atom

[devayaani]

Can you enlighten me, please?
I will stick with the basic structure of the atom (of a nucleus with its protons and neutrons) and electrons moving in their orbitals.
This fundamental structure of an atom (without getting into quarks etc)- is it deduced by the experiments and is agreed as a model of atom or has anyone actually (I mean optically in an electron microscope for example) seen an atom?
If optically seen, which element's atom was optically seen? By whom? (I presume the size of an atom will increase as the atomic number increases.)
This is bothering me as I always thought the atom is not optically visualised so far.
Thanks in advance.

[Clanad]

Some results of experiments are, surprisingly ancient, by todaoy's rapidly expanding knowledge base scales...

Heres' one:

http://www.zurich.ibm.com/news/04/chargestates .html

And here's another:

http://www.ornl.gov/info/press_releases/get_pr ess_release.cfm?ReleaseNumber=mr20040917-00

[Ice.Maiden]

I think Erwin Muller first invented the Field Ion Microscope (FIM), by which atoms from gases could be studied, but I can't remember how this worked now.

[eltelioni]

Optical microscopy and electron microscopy are very different things. In optical microscopy you are using light that your eye can detect . The samllest thing you can see this way is approximately 1000 atoms across. As Clanad's references show, using an electron microscope you can just about "see" atoms but you are not "seeing them optically". The electron microscope scans the target with a very narrow beam of electrons and sensors detect the reflected electrons. In the examples given, a computer is used to derive an image from the sensor outputs.

[jake-the-peg]

It is difficult to "see" an atom because basically what you can see optically is limited by the wavelength of the light you use to observe it.

Over the years ways to get around this have been developed - most famously the electron microscope that uses beams of electrons.

Now this brings us to the question of what you mean by optically seen.

Now I can look out of the window and see a tree but without a microscope I can't see a bacteria. As we get smaller I need to look with beams of electrons as in the electron microscope or with probes like the scanning tunneling electron microscope.

In the same way Rutherford "saw" the nucleus when some of the radioactive particles he sent into a gold foil bounce right back.

So you have to think somewhat carefully about what you mean by optically seen.

You might also care to look at this

http://www.particlephysics.ac.uk/news/picture- of-the-week/picture-archive/tracks-in-a-hydrog en-bubble-chamber/000329_sm.jpg

These are the tracks made by subatomic particles colliding

Is this seeing?

Just something to think about

[fo3nix]

Just to add.

Since we, as humans, detect things in a very optical way by 'seeing', we tend to try and see if we can optically detect things too.

But really, all we want to do is detect whatever it is. It doesn't matter whether we detect this via sound waves, light, or whatever. It's the detection, to strengthen theory and current knowledge, that matters.

[beso]

There are other remarkable microscope technologies that can produce images that include the atomic sized bumps in a surface.

They use a ultra sharp needle to scan the surface of the sample and produce an image based on the movements of the needle.

The Atomic Force Microscope presses on the surface and feels the repulsion of the nuclei in the surface and the needle. Essentially it is like a miniature version a blind man imaging something repeatedly by poking it with a sharp stick.

The Scanning Tunnelling Microscope uses a similar principle but moves an electrically charges needle point above the surface so close that electrons jump the gap due to Quantum Tunnelling. Tunnelling occurs when the random position of an electron makes it turn up on the wrong side of the tiny gap. The current is exquisitely sensitive to distance.

Both devices scan the surface while maintaining either a constant force or constant current. The mechanism that drives the scanning can also measure the vertical position which is used to create the image.

[beso]

continued:

Another variant uses a needle with a tiny thermocouple in the tip. It scans the surface which is simultaneously being illuminated with a scan of electromagnetic frequencies. When the frequency matches the absorption frequency of a particular molecule the area heats up slightly and the temperature rise is detected by the thermocouple. Hence the type of molecule under the tip can be determined.

Consider the problems such as external vibrations that needed to be overcome to maintain the precise movements. The microscopes float in mercury and use magnetic eddy current dampers.

Imagine trying to position a needle with such incredible precision. Both the scanning and vertical positioning is doen with a single peizioelectric tripod.

The tungsten needles for the Atomic Force and Tunnelling microscopes are made by blasting a mechanically sharpened point with electric discharges and testing them until they work, indicating a single atom is at the tip.

The framework is made of laboratory glass. They are beautiful and elegant instruments which I place it at the pinnacle of human achievement. This technology sounds unbelievable yet it was invented about 1980. Its inventors quite deservedly received a Nobel Prize.

[devayaani]

Thank you all for explanation and providing em with the relevant website links.