Individual Atom Memory Created

azav writes "University of Wisconsin-Madison Scientists have created "atomic scale" memory using individual atoms of Silicon." A cool photo can be found on the site as well.

Comments

Sizes of atoms.

[Christopher Thomas]

Actually, they are all rougly the same size, regardless of atomic weight. This is one of the interesting things about quantum mechanics and atomic physics. *All* atoms are between 0.5 and 2.5 Angstroms (1e-10 m)with Cesium being the largest (bigger than Uranium) and Nitrogen? being the smallest. Silicon isn't very large, however.

Hydrogen's the smallest, according to my books, with a radius of something like 0.53 angstroms (been a while since I looked it up).

What confuses me is why the atomic radii don't go up as the square of the number of shells. The alkali metals will have a single electron in the outermost shell, with the nucleus shielded by the inner shells, and so having an apparent charge of one. This seems to give a system with size equivalent to the nth energy level of an electron in hydrogen, which goes up as the square of the shell number.

I and the friends I asked about this speculate that because the electrons in the sheilding shells are smeared out radially, the outermost shielding shell extends past the valence shell's nominal radius, and so the core is only partly shielded, but I haven't seen any description to date of how you work out what the radii actually end up being.

Any pointers/quick explanations?