Study Notes on Solids

Classification of Solids

• Solids are classified as:

  • Amorphous

  • Example: Glass (window panes, Pyrex)

  • Disorder in structure; different sections show different structures.

  • Crystalline

  • Regular arrangement of components; sections show consistent structures.

Unit Cells

• Unit Cells: Repeating units in crystalline solids that form a lattice.

• Types of Crystalline Solids:

  • Ionic Solids:

  • Example: Sodium chloride (NaCl); ions sit at lattice points.

  • Molecular Solids:

  • Example: Sugar (glucose molecules at lattice points).

  • Held together by intermolecular forces, not covalent bonds.

  • Atomic Solids:

  • Atoms at lattice points, can be covalent or held by intermolecular forces.

  • Examples: Diamond (atomic crystalline), Ice (complex structure).

  • Metallic Solids: Subclass of atomic solids; discussed briefly.

  • Network Solids:

  • Example: Silicon dioxide; covalent bonds between atoms.

Types of Unit Cells

• Simple Cubic:

  • Atoms/ions at each corner.

  • 1 atom per unit cell.

• Body-Centered Cubic (BCC):

  • Atom in the center of the cube.

  • More complex than simple cubic.

  • 2 atoms per unit cell.

• Face-Centered Cubic (FCC):

  • Atoms on each face of the cube.

  • 4 atoms per unit cell.

Density and Atom Contribution

• Density increases from simple cubic to FCC.

• Contributions:

  • Corner atoms contribute $\frac{1}{8}$ each.

  • Face atoms contribute $\frac{1}{2}$ each.

  • Center atom contributes 1 whole.

• Total atom calculation per unit cell:

  • Simple Cubic: 1

  • BCC: 2

  • FCC: 4

Summary Statement

• Familiarity with the types and structures of solids and their unit cells is crucial for understanding materials science.