Solids- 2 PUC Chemistry

Classification of Crystalline Solids

Based on the nature of intermolecular forces, crystalline solids are classified into four categories −

Molecular solids

• Ionic solids
• Metallic solids
• Covalent solids

• Molecular solids

• Constituent particles are molecules

Ionic solids

• Constituent particles are ions
• Hard but brittle
• Insulators of electricity in solid state, but conductors in molten state and in aqueous solution
• High melting point
• Attractive forces are Coulombic or electrostatic
• Example − NaCl, MgO, ZnS

• Metallic solids
  • In metallic solids, positive ions are surrounded and are held together in a sea of delocalised electrons.
  • Hard but malleable and ductile
  • Conductors of electricity in solid state as well as molten state
  • Fairly high melting point
  • Particles are held by metallic bonding
  • Example − Fe, Cu, Mg
• Covalent or network solids
  • Constituent particles are atoms
  • Hard (except graphite, which is soft)
  • Insulators of electricity (except graphite, which is a conductor of electricity)
  • Very high melting point and can decompose before melting
  • Particles are held by covalent bonding
  • Example − SiO₂ (quartz), SiC, diamond, graphite