The Structure of Solids (College Board AP® Chemistry)

The Structure of Solids

• Solids are a nearly incompressible state of matter with well defined shapes

  • This is because they are made of atoms, molecules and ions which are in close contact and in fixed positions

  • These particles do not move relative to each other

    • This explains why solids do not flow, unlike liquids

• We can visualize a solid as being formed by stacking a large number of small, identical structural units, in the same manner as building a wall by stacking identical bricks

• Structurally, solids can be divided into two categories:

  • Crystalline

  • Amorphous

• Solids in which atoms are arranged in an orderly repeating pattern are called crystalline solids

  • The arrangement of particles in a crystalline solid is such that the net attractive intermolecular forces are at their maximum

  • The forces responsible for the stability of a crystal can be

    • Ionic forces

    • Covalent bonds

    • Van der Waals forces

    • Hydrogen bonds

    • Or a combination of these forces

  • When most liquids are cooled, they eventually freeze and form crystalline solids

  • Examples of crystalline solids include sodium chloride, sucrose, ice and diamond

• An amorphous solid has a disordered structure; it lacks the well-defined arrangement of basic units found in a crystal

  • The structures of amorphous solids are similar to those of liquids on an atomic level, but the molecules, atoms and / or ions lack the freedom of motion they have in liquids

  • They may be formed when liquids cool too quickly before their molecules become arranged in an orderly pattern

  • Common examples of amorphous solids are rubber, glass and obsidian

Structures of crystalline and amorphous solids

The particles in solids may be arranged in a regular repeating pattern (crystalline) or randomly (amorphous)