Solid structures

• Ionic solids (crystals)


  Giant lattices of positive and negative ions with structures made of the same base unit repeated over and over again. The structure depends on the relative number of ions and their sizes
• Cs+ ion compared to Na+ ion

  Cs+ ion is larger than Na+ ion, allowing more Cl– ions to fit around it
• Physical properties of Ionic solids

  • High melting and boiling temperatures due to strong electrostatic forces between oppositely charged ions
  • Often soluble in water as water molecules are attracted to the positive and negative ions
  • Hard but brittle, with layers of ions sliding over each other causing repulsion and shattering
  • Poor electrical conductivity when solid, but good when molten or dissolved
• Giant covalent solids


  Consist of networks of covalently bonded atoms arranged into giant lattices
• Diamond structure


  Each carbon atom is joined to four others by strong covalent bonds arranged in a tetrahedral shape, making it very hard
• Physical properties of Diamond

  • Very high melting temperature due to numerous strong covalent bonds
  • Does not conduct electricity due to the absence of free electrons or ions
• Graphite structure


  Consists of hexagonal layers with each carbon joined to three others by strong covalent bonds, with extra electrons delocalised within the layer
• Physical properties of Graphite

  • Very high melting temperature due to strong covalent bonds in the hexagon layers
  • Soft and slippery due to easily broken weak forces between layers allowing sliding
  • Good conductor of electricity due to delocalised electrons free to move along the layers
• Coordination numbers in NaCl and CsCl

  • NaCl coordination number 6:6
  • CsCl coordination number 8:8
• Metallic structures


  Metal atoms bond together to form a giant metallic structure with metal cations surrounded by a 'sea' of delocalised electrons due to strong metallic bonds from electrostatic forces of attraction between cation nuclei and the delocalised electrons
• Metallic bond


  Electrostatic forces of attraction between the nucleus of the cations and the delocalised electrons
• Metallic structures


  • Metal atoms bond together to form a giant metallic structure
  • Metals consist of a regular arrangement of metal cations surrounded by a 'sea' of delocalised electrons
  • Strong metallic bond due to electrostatic forces of attraction between the nucleus of the cations and the delocalised electrons
• Physical properties of metals

  • High melting temperatures
  • Hard
  • Good conductors of electricity in solid and molten state
  • Good thermal conductors
  • Malleable and ductile
• Conductivity of metals


  Delocalised electrons can carry a current because they will be attracted to and move towards the positive terminal of the cell
• Malleability and ductility of metals

  Layers of cations can slide over each other; delocalised electrons move with the cations preventing forces of repulsion between layers
• Simple molecular structures


  • Consist of covalently bonded molecules held together by weak intermolecular forces
  • Low melting and boiling temperatures
  • Poor conductors of electricity
• Simple molecular solids


  • iodine
  • ice
• Iodine structure


  • Atoms covalently bonded in pairs to form diatomic I2 molecules held together by weak van der Waals forces
• Ice structure


  • Molecules of water arranged in rings of six held together by hydrogen bonds; less dense than liquid water at 0˚C