Edexcel A Level Chemistry:复习笔记1.4.4 Physical Properties of Ionic Compounds

Physical Properties of Ionic Compounds


  • Most ionic, metallic and covalent solids are crystalline lattices
  • The ions, atoms or molecules are arranged in a regular and repeating arrangement

Giant ionic lattices

  • An ionic bond is an electrostatic force of attraction between a positively charged metal (cation) ion and a negatively charged non-metal (anion) ion
    • The metal becomes positively charged as it transfers electrons to the non-metal which then becomes negatively charged
    • When an ionic compound is formed, the attraction between the ions happens in all directions


  • Ionic compounds are arranged in giant ionic lattices (also called giant ionic structures)
  • The type of lattice formed depends on the sizes of the positive and negative ions which are arranged in an alternating fashion
    • The ionic lattice of MgO and NaCl are cubic



Ionic lattices of the ionic compounds NaCl and MgO



Electron density maps shown above show the likelihood of finding electrons in a region. This shows the electron density map for NaCl. The contours are lines of equal electron density. A = Na+ ions (smaller), B = Cl- ions (larger). Between the ions the electron density falls to zero.



General ionic lattice which shows the actual packing of the ions



  • The behaviour of ionic substances during electrolysis is a clear piece of evidence for the existence of ions
    • Positive ions in solution are attracted to the negative electrode
    • Negative ions in solution are attracted to the positive electrode

Electrolysis-aqueous-solutionsSet up of electrolysis


  • An example which is simple to see the separation is using copper(II) chromate(VI), CuCrO4
  • The solution contains
    • Cu2+ ions (blue)
    • CrO42- ions (yellow)ion-migration
  • Overall the solution is an olive green colour, but when the solution undergoes electrolysis a blue colour appears around the negative electrode, and a yellow colour appears around the positive electrode
  • This is because the Cu2+ ions are attracted to the negative electrode and their blue colour is observed and the CrO42- ions are attracted to the positive electrode and their yellow colour is observed