Q4 The Crystal Lattice and the Unit Cell

• Unit Cell


  The smallest portion of the crystal which shows the complete pattern of its particles
• Crystal Lattice


  Formed when unit cells are repeated in all directions
• Parallelepipeds


  Six-sided figures whose faces are parallelograms
• Basic Types of Unit Cells


  • Cubic
  • Tetragonal
  • Orthorhombic
  • Monoclinic
  • Rhombohedral
  • Hexagonal
  • Triclinic
• Cubic


  • Galena (Lead(II) sulfide)
• Tetragonal


  • Zircon (ZrSiO4)
• Orthorhombic


  • Topaz (Al2SiO4(F, OH)2
• Monoclinic


  • Gypsum (CaSO4•2H2O)
• Rhombohedral


  • Calcite (CaCO3)
• Hexagonal


  • Tourmaline
• Triclinic


  • Amazonite (K(AlSi3O8))
• 3 Kinds of Cubic Unit Cells

  • Simple Cubic
  • Body-centered cubic
  • Face-centered cubic
• Simple Cubic


  • Unit cell has an atom at each of the eight corners of the cube
• Body-centered cubic


  • Has an additional atom in the center of its cube
• Face-centered cubic


  • Has additional atoms on each of its six faces where each is shared with another neighboring cube