Themes > Science > Physics > Solid State Physics > Atomic Bonding and Crystal Structure > Atomic Bonding Mechanisms > Categories of Solids > Categories of Solids Based on the Solid Pack

Solids can be divided into three categories on the basis of how the particles that form the solid pack.
  • Crystalline solids are three-dimensional analogs of a brick wall. They have a regular structure, in which the particles pack in a repeating pattern from one edge of the solid to the other.
  • Amorphous solids (literally, "solids without form") have a random structure, with little if any long-range order.
  • Polycrystalline solids are an aggregate of a large number of small crystals or grains in which the structure is regular, but the crystals or grains are arranged in a random fashion.

The extent to which a solid is crystalline has important effects on its physical properties.

Examples: The polyethylene used to make sandwich bags and garbage packs is an amorphous solid that consists of more or less randomly oriented chains of (-CH2-CH2-) linkages. Milk bottles are made from a more crystalline form of polyethylene, and they have a much more rigid structure.


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