Why do atoms just have a general vicinity of which they rest in a solid?
A mass of electrons
My theory is that in a solid of like atoms, all of the electrons tend to be shared, forming a giant cloud of electrons that are shared among each other, and with all these negative electrons buzzing around, and positive nuclei, the atoms just kind of hold each other in place.
If you look at images from scanning tunneling or atomic force microscopes of solids, you can generally make out a regular crystal pattern. So, the atoms are localized fairly well in a crystal.
It's a consequence of the fact that, until measured, particles do not have specific locations, and instead have an area of space that they "occupy". I put that in quotations because I want to emphasize that defining the position of a particle is much more complicated than one might think.
Do you know anything about Quantum Mechanics, such as the Uncertainty Principle or what a wave function is?
Typically it is because they are bound together by some force. For ionic crystals it is an electrostatic force. For covalent molecules it is the exchange of the valence electrons. For metals it is the overall sharing of the "Drude cloud" of free electrons.
Note that the nucleus of any atom is thousands of times heavier than an electron, so their inertia will keep them localized even though they do have some motion. If their motion becomes too great (thermal motion) the material melts, and you no longer have a solid.
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