TYPES OF PROPERTIES OF CRYSTALLINE SOLIDS

• Crystalline solids


  Arranged in a definite repeating pattern held together by uniform, strong intermolecular forces
• Crystalline solids have different types and properties
• The use of crystalline solids can be explained by their type and properties
• Unit cell


  The small repeating unit in the structure of crystalline solids, composed of lattice points that represent the locations of ions or atoms
• Crystal lattice


  The arrangement of the geometrical patterns of points in the unit cell
• Motif


  An atom or a group of atoms that is repeated at each lattice point to generate a crystal structure
• 2D lattice unit cell

  • Parallelogram with two lattice vectors (a and b), four primitive lattices (square, rectangular, hexagonal, and oblique)
• 3D lattice unit cell

  • Parallelepiped with three lattice vectors (a, b, and c) and three lattice angles (α, β, and γ), seven primitive lattices (cubic, hexagonal, tetragonal, rhombohedral, orthorhombic, monoclinic, and triclinic)
• Cubic lattice


  • a = b = c; α = β = γ, primitive cubic lattice, body-centered cubic lattice, face-centered cubic lattice
• Types of crystalline solids

  • Metallic
  • Covalent network
  • Molecular
  • Ionic
• Metallic solids/metals


  Consist entirely of metal atoms, strong bonding due to dispersion forces, metallic bonding (uniform distribution of atomic nuclei within a "sea" of delocalized electrons)
• Metallic solids/metals


  • Adopt structures with symmetric close-packed arrangements of atoms, high electrical and thermal conductivity, malleable, ductile, varying melting points
• Pure gold is not suitable for making jewelry
• Covalent network solids


  Made up of atoms held together by a network of covalent bonds, can be made of one or more different atoms, valence electrons used to form covalent bonds
• Covalent network solids


  • Poor conductors, typically characterized by strength, hardness, and high melting points
• Covalent network solids


  • Diamond
  • Graphite
• Diamond


  Made up of carbon atoms, hardest known material, 3D crystals, good thermal conductor
• Graphite


  Made up of carbon atoms, 2D covalent network solid, can form flat sheets, good electrical conductor
• Allotropy


  The ability of a single element, atom, or molecule to form multiple structures of solids
• Although the majority of the covalent network solids have poor conductivity, graphite is considered a good conductor
• Molecular solids


  Made up of covalently bonded atoms or molecules that are held together by intermolecular forces such as van der Waals, valence electrons used in bonding, poor conductors (insulators), soft
• Molecular solids


  • The strengths of attractive forces between units vary widely, most are nonpolar, molecular solids with permanent dipoles (polar molecules) melt at a higher temperature and easily dissolve in water
• Ionic solids


  Composed of positive (cation) and negative (anions) ions that are held together by electrostatic attractions, difficult to break, high melting points
• Electrostatic attractions in ionic solids are stronger compared to van der Waals forces in molecular solids
• Ionic solids are poor conductors in solid form but conduct when molten or dissolved as their ions are free to move
• Polar molecular solids


  Have higher melting points than nonpolar molecular solids