1.5

• Ionic solids


  Consist of a regular arrangement of positive and negative ions. The structure is repeated over and over again.
• Crystal structure


  Depends on the relative number of ions and their size. Structures are such that the electrostatic attraction between oppositely charged ions is greater than the electrostatic repulsion between ions with the same charge.
• Sodium chloride


  Each Na+ ion is surrounded by six Cl- ions and vice versa. The coordination number of each ion is 6.
• Sodium chloride


  • Ball and stick model
  • Space filling model
• Caesium chloride


  The Cs+ ion is larger than the Na+ ion, therefore more Cl- ions can fit around it. Each Cs+ ion is surrounded by eight Cl- ions and vice versa. The coordination number of each ion is 8.
• Physical properties of ionic solids


  • High melting temperatures
  • Often soluble in water
  • Poor electrical conductivity in solid state, but good when molten or dissolved
• Giant covalent solids


  Consist of networks of covalently bonded atoms that extend throughout the whole structure. Also called macromolecules.
• Diamond


  Each carbon atom is covalently bonded to four others in a tetrahedral arrangement. The bonding is uniform throughout the structure.
• Physical properties of diamond


  • Very high melting temperature
  • Extremely hard
  • Insoluble in water
  • Poor conductor of electricity
• Graphite


  Consists of layers of hexagonal rings. Each carbon atom is joined to three others by strong covalent bonds. The fourth electron from each carbon atom is delocalised within the layer.
• Physical properties of graphite


  • Very high melting temperature
  • Soft, slippery feel
  • Insoluble in water
  • Good conductor of electricity parallel to layers
• Simple molecular solids


  Have covalent bonds within molecules held together by weak intermolecular forces.
• Physical properties of simple molecular solids


  • Low melting and boiling temperatures
  • Soft
  • Normally insoluble in water, but can form hydrogen bonds
• Simple molecular solids


  • Iodine
  • Ice
• Metallic bonding


  Metal atoms lose control over their outer electrons, which become delocalised and free to move throughout the metal. This leaves a lattice of positive metal cations surrounded by a 'sea' of delocalised electrons.
• Physical properties of metals


  • High melting temperatures
  • Hard
  • Insoluble in water
  • Good conductors of electricity and heat
  • Malleable and ductile
• Potassium iodide has the same crystal structure as sodium chloride