http://www.u-helmich.de/che/09/04-ionen/ionen07.html (http://www.u-helmich.de/che/09/04-ionen/ionen07.html)
maybe you could explain at this point why elementary sulfur (for example) does form crystals?
Sulfur forms extremely strong bonds to itself. Its called catenation. It forms rings of 8 sulfur atoms. It does this because it has 4 sp3 hybridised orbitals, two have a lone pair of electrons and two have one electron which form bonds with the single electron of another S atoms sp3 orbital. Hence the formation of two bonds, leading to rings. 8 most stable arrangement - bond angles must be at lowest energy conformation with 8 S atoms. Because things tend to move towards lowest energy state, other allotropes of S rings tend to become S8 rings. Because atoms tend towards lowest energy conformation, molecules stack as orderly as possible: = crystal formation. There is a pretty simple explaination without really going into thermodynamics of it all... 8)