I was taught that atoms are NOT like little billiard balls, STM pics of atoms look like little billiard balls!

Question

Why do images of atoms look like little balls? If (as I suspect) we're seeing the outermost electron shell of the atom, why are they all spherical? And since the 'shell' isn't really a shell, what are we seeing?

Answer 1

I think the reason that STM images of atoms look like little balls is because what you are actually seeing is the electron cloud of the atoms. I don't believe we have any sort of optical imaging technology capable of photographing atoms where their electrons are just merely standing still in space. Instead, the images you see are a composite of where the electrons were whizzing about when the image was being taken.

As for the reason that they look spherical and not like d-orbitals or whatever, you still have to remember that those orbitals are still probability shells and not definite shapes of the paths that the electrons will take; it just shows that 90% of the time, the electron will be somewhere within that orbital shape. When you combine it all together more or less, it'll look like a sphere; you're not going to see the individual orbiatls on each principal quantum number.

Answer 2

Little billiard balls have a well-defined, hard boundary. Atoms have a fuzzy boundary, and if you apply pressure you can push them closer together. And they're not all spherical. The wave function of, for instance, a hydrogen atom is spherically symmetrical, but the valence electrons of a carbon atom stick out like the lines from the centre of a tetrahedron to its 4 corners, at an angle of 109.5 degrees to each other, and they're shaped like 4 long pear-shaped party balloons with the thin ends tied together. STM pics of atoms only look spherical because the resolution is low.

Answer 3

The images you see from an stm are the result of computer programs that interpret data gathered by minuscule shifts in current as a conductive tip passes extremely close to a surface. These changes occur in a very regular fashion.

The true geometry of an atom is described by the wave equations for its electrons.