EL 5 

==Covalent bonding-== electrons are shared between atoms on non-metallic elements (not energetically favourable to form ions). The compound is more stable than the elements individually.
==Lone pairs-== pairs of electrons that are not involved in bonding
Calculating the lone pairs

• Work out the number of valence electrons of the element
• Work out how many of those electrons are involved in bonding to another atom
• Subtract the number of bonding electrons from the number of valence electrons
• Ass electrons for every negative charge
• Subtract electrons for every positive charge
• Divide the number by 2 to get the number of lone pairs for the element
• You have to take into account the type of bond (eg. Single, double) and the charge on the molecule.
  ==Dative covalent bond==- when both bonding electrons come from the same atom.
  Determining shapes
  In molecules, bonding pairs of electrons arrange themselves as far apart as possible.
  Lone pairs have a greater repulsion than bonding pairs, therefore the presences of lone pairs can alter the shape of the molecules by pushing the bonding pairs closer together.

6 areas of electron density = octahedral molecule with a bond angle of 90 degrees
5 areas of electron density = trigonal bipyrmidal molecule with a bond angle of 120 degrees and 90 degrees
4 areas of electron density = tetrahedral molecule with a bond angle of 109.5 degrees
3 areas of electron density = trigonal planar molecule with a bond angle of 120 degrees
2 areas of electron density = linear molecules with a bond angle of 180 degrees
If one of the areas of electorn density is a lone pair it will repell the other electrons by an extra 2.5 degrees