2,2,2 Sodium Chloride as a typical Ionic Solid
Crystals
Crystalline They have regular geometric shapes Lattice structure made up of positive and negative ions Shape depends on arrangements of these ions Arrangement depends on relative size and relative abundance of each type of ion Ions are tiny – positive ions are smaller than the corresponding atoms
Crystal Lattice Sodium ion Chloride ion
Face-centred Cube Sodium ions are smaller than Chloride ions 2 shells as opposed to 3 shells Ratio 1 Na+ : 1 Cl- Relative size and number of each ion determines arrangement Face-centred cube
Properties of Ionic Compounds
Melting and Boiling Points High Boiling and Melting Points Each ion held in place by 5 oppositely charged ions There fore difficult to break away
Conductivity Do not conduct when solid because electrons tightly held in full outer shells Ions are trapped by six oppositely charge ions Conduct with electrolysis when molten (fused) or in solution Ions are free to move in both conditions and have electrons added at cathode and pulled off at anode causing the chemical reactions
Solubility Many soluble in water due to polar nature of water Insoluble in organic solvents such as benzene and cyclopropane because these are covalent and like dissolves like
- - - - - Brittle + + + Force Hard as difficult to move because every ion is firmly held by 6 other ions with opposite charge Once they move the tiniest amount – the like charges line up and repel, and crystal shears along a plane + - Force - + - - - +
Ionic materials in everyday life You need to know two uses Salt [sodium chloride] tablets are taken especially in hot climates to replace salt lost by sweating. Iron sulphate tablets are taken to treat anaemia which has many causes. The iron is needed to make blood as it occupies the centre of haemoglobin molecules