Solid structures

• Ionic solids (crystals)


  Giant lattices of positive and negative ions
• Ionic solids


  • Structures are made of the same base unit repeated over and over again
  • The structure of the crystal depends on the relative number of ions and their sizes
• Cs+ ion is larger than Na+ ion


  More Cl– ions can fit around it
• Physical properties of ionic solids

  • High melting and boiling temperatures
  • Often soluble in water
  • Hard but brittle
  • Poor electrical conductivity when solid, but good when molten or dissolved
• It takes a large amount of energy to overcome the strong electrostatic forces between the oppositely charged ions in ionic solids
• The oxygen end of the water molecules is attracted to the positive ions, and the hydrogen ends of the water molecules are attracted to the negative ions in ionic solids
• When force is applied to ionic solids, layers of ions slide over each other causing ions of the same charge to be next to each other; the ions repel each other and the crystal shatters
• In the solid state, the ions in ionic solids are fixed in position by the strong ionic bonds; however, when molten or dissolved, the ions are free to move and will move to the electrode of opposite charge, so will carry the current
• Giant covalent solids


  Networks of covalently bonded atoms arranged into giant lattices
• Diamond


  • Each carbon atom is joined to four others by strong covalent bonds
  • The atoms arrange themselves in a tetrahedral shape
• Diamond


  • Very high melting temperature
  • Does not conduct electricity
• Graphite


  • Each carbon is joined to three others by strong covalent bonds
  • The extra electrons are delocalised within the layer
  • The layers are held together by weak van der Waals forces
• Graphite


  • Very high melting temperature
  • Soft and slippery
  • Good conductor of electricity
• Metallic solids


  • Metal atoms bond together to form a giant metallic structure
  • Metals consist of a regular arrangement of metal cations (a lattice) surrounded by a 'sea' of delocalised electrons
  • The strong metallic bond is due to the electrostatic forces of attraction between the nucleus of the cations and the delocalised electrons
• Physical properties of metallic solids

  • High melting temperatures
  • Hard
  • Good conductors of electricity both in the solid and molten state
  • Good thermal conductors
  • Malleable and ductile
• The melting temperature of metallic solids is affected by the number of delocalised electrons per cation and the size of the cation
• Simple molecular solids


  Consist of covalently bonded molecules held together by weak intermolecular forces
• Physical properties of simple molecular solids

  • Low melting and boiling temperatures
  • Poor conductors of electricity
• Iodine


  • Atoms are covalently bonded in pairs to form diatomic I2 molecules
  • These molecules are held together by weak van der Waals forces and are arranged in a regular pattern
• Ice


  • Molecules of water are arranged in rings of six held together by hydrogen bonds
  • The water molecules are further apart than they are in the liquid state, so ice is less dense than liquid water at 0˚C