Structure and bonding

• Relative charge of a proton, neutron, electron

  +1, 0, -1
• Relative mass of a proton, neutron, electron

  1, 1, 1/2000
• The atomic number is the

  number of protons in an atom
• The mass number is

  The number of protons and neutrons
• Steps to finding the shape of a molecule

  1. Find number of electron pairs
  2. determine how many pairs are bonding how many are lone
  3. Bonding shows basic shape, lone shows any additional repulsion
• shape of 2 bonding

  linear
• Shape of 2 bonding 2 lone

  non-linear
• Shape of 3 bonding

  trigonal planar
• Shape of 4 bonding

  Tetrahedral
• Shape of 6 bonding

  Octahedral
• Shape of 3 bonding 1 lone

  Pyramidal
• Linear bond angle

  $180^{\circ}$
• Non-linear bond angle

  $104.5^{\circ}$
• Trigonal planar bond angle

  $120^{\circ}$
• Tetrahedral bond angle

  $109.5^{\circ}$
• Octrahedral bond angle

  $90^{\circ}$
• Pyramidal bond angle

  $107^{\circ}$
• Question eg. Explain why the molecule has this bond angle

  1. Electron pairs repel as far as possible
  2. Lone pairs repel more
• Ionic bonding

  Is an electrostatic attraction between positive and negative ions
• Ionic bonding occurs between

  A metal and non metal - positive and negative ions
• Ionic bonding forms a

  Giant ionic lattice with electrostatic forces
• Ions with a greater charge have a greater attraction to other ions resulting in stronger ionic bonding
• The larger an ion is the greater the ionic radius and so the weaker the attraction as the attraction has to act over a greater distance
• Physical properties of ionic bonding

  • High melting and boiling point - Due to strong electrostatic forces of attraction which require lots of energy to overcome
  • Conduct electricity when melted or dissolved - Due to ions no longer held in a lattice and can act as mobile charge carriers
• Covalent bonding

  A strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms
• Covalent bonds form between

  Two Non-metals
• Multiple covalent bonds can form between two molecules. - double and triple bonds
• Shorter covalent bonds are stronger as atoms are held closer together so forces of attraction are greater
• Double and triple bonds are shorter than single bonds so are much stronger
• Average bond enthalpy

  Used to measure covalent bond strength
• Dative bonds

  Formed when both electrons in the shared pair come from one atom instead of one coming from each
• The properties of a dative bond are the exact same as a standard covalent bond
• Ammonium

  NH4(+)
• Hydroxide

  OH(-)
• Nitrate

  NO3(-)
• Hydrogen carbonate

  HCO3(-)
• Carbonate

  CO3(2-)
• Sulfate

  SO4(2-)
• Phosphate

  PO4(3-)
• Elecronegativity

  The attraction of a bonded atom for the pair of electrons in a covalent bond