If the space between atoms is so vast, why do solids exist?

Answer 1

Here is how I think of it.

In everyday life we are accustomed to solids, liquids, and gas. We think of solids and liquids as very tangible. Gases are less so, but all you need to do to remind yourself that gases are also quite tangible is exhale quickly into your palm or walk outside on a windy day.

At the atomic level analogies to everyday experience are not strong. It's true that the nucleus of an atom is a tiny portion of the size of an atom, but it's misleading to think of the space between the nucleus and electrons as empty. Forces acting between the nucleus and electron determine its size. The space is in a sense not taken up by particles with mass but by the forces interacting between them.

It is a trivial matter to take something from your desk and throw it across the room. At the level of everyday experience such actions are easy because nothing is preventing such free movement. At the atomic level it is very challenging to move objects with mass closer together. Solids thus are more than about point masses; they are also about how point masses form rigid structures relative to each other and resist efforts to be compacted closer together.