Chapter 6

• Electron pairs repel each other so they are as far apart as possible


  Electron pair repulsion theory
• 109.5


  Tetrahedral bond angle
• 4


  Bonded pairs in tetrahedral shape
• 0


  Lone pairs in tetrahedral shape
• 107


  Pyramidal bond angle
• 3


  Bonded pairs in pyramidal shape
• 1


  Lone pairs in pyramidal shape
• 104.5


  Non-linear bond angle
• 2

  Bonded pairs in non-linear shape
• 2


  Lone pairs in non-linear shape
• Electron pairs repel each other as far apart as possible. Number of pairs of electrons determine shape


  How can you determine the shape of a molecule?
• 180


  Linear shape bond angle
• 2


  Bonded pairs in linear shape
• 0


  Lone pairs in linear shape
• 120


  Trigonal planer bond angle
• 3


  Bonded pairs in trigonal planer shape
• 0


  Lone pairs in trigonal planer shape
• 90


  Octahedral bond angle
• 6


  Bonded pairs in octahedral shape
• 0


  Lone pairs in octahedral shape
• The ability of an atom to attract the bonding pair in a covalent bond


  Electronegativity
• Pauling scale


  How is electronegativity measured?
• Flourine with a Pauling value of 4.0


  Most electronegative element
• The electron pair is shared equally

  Non-polar bond
• The bonded atoms are the same, or they have similar electronegativity


  A bond will be non-polar when...
• The electron pair is shared unequally


  Polar bonds
• Nuclear charge, atomic radius and shielding effect


  Which factors affect electronegativity?
• Decreases


  Down a group, electronegativity...
• Increases


  Across a group, electronegativity...
• Difference in electronegativity of atoms


  Permanent dipole
• Dipoles reinforce one another to produce an overall dipole


  Polar molecules
• Act between all molecules, and are the weakest type of intermolecular force


  Induced dipole-dipole interactions
• Electrons move randomly, creating instantaneous dipoles. This induces a dipole on a neighbouring molecule, and they will attract one another


  How do IDD (London) forces form?
• A weak attractive force between permanent dipoles on neighbouring molecules.


  Permenant Dipole-Dipole Interactions
• Small molecules with a definite molecular formula


  Simple molecular lattice
• Low.


  Melting and boiling point of simple molecules
• Polar solvents dissolve polar molecules. Non-polar solvents dissolve non-polar molecules


  Solubility of simple molecules
• All covalently bonded and held together by London forces


  Why are the melting and boiling point of simple molecules low?
• A PDD force between hydrogen and oxygen, nitrogen or flourine.


  Hydrogen Bonding
• Hydrogen bonds


  Which intermolecular force is the strongest?