The Structure of Solids (College Board AP® Chemistry): Revision Note

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 vibrate about fixed positions but do not move past each other

    • This explains why solids do not flow, unlike liquids

• A crystalline solid can be pictured as many small, identical structural units stacked together, like identical bricks in a wall

• Structurally, solids can be divided into two categories:

  • Crystalline

  • Amorphous

• Solids in which the particles (atoms, ions or molecules) are arranged in an orderly repeating pattern are called crystalline solids

  • The particles in a crystalline solid are arranged so that the attractions between them are as strong as possible

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

    • Ionic forces

    • Covalent bonds

    • London dispersion forces and dipole-dipole forces

    • Hydrogen bonds

    • a combination of these forces

  • The structure of a solid also depends on how well its particles can pack together

  • 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)