- Polymorphism is the ability of a solid to exist in more than one crystal form. For example, water ice is ordinarily found in the hexagonal formIce Ih, but can also exist as the cubic Ice Ic, the rhombohedral ice II, and many other forms.
- Amorphous phases are also possible with the same molecule, such as amorphous ice. In this case, the phenomenon is known aspolyamorphism.
- For pure chemical elements, polymorphism is known as allotropy. For example, diamond, graphite, and fullerenes are different allotropes of carbon.
|Crystal||Particles||Attractive forces||Melting point||Other properties|
|Ionic||Positive and negative ions||Electrostatic attractions||High||Hard, brittle, good electrical conductor in molten state|
|Molecular||Polar molecules||London force anddipole-dipole attraction||Low||Soft, non-conductor or extremely poor conductor of electricity in liquid state|
|Molecular||Non-polar molecules||London force||Low||Soft conductor|