Question

What is the difference between crystalline and amorphous solids?

Answer 1

A typical crystalline solid is held together by strong intermolecular forces (IMFs), and can usually be found as unit cells repeated in 3 dimensions (i.e. lattice structures).

An amorphous solid like glass or plastics has a less patterned structure, but is rigid nonetheless, and also has strong IMFs.

Because of those strong IMFs, many solids have rigid structures. By definition, rigid structure `->` fixed shape `->` fixed volume.

You can find more about properties of solids here.