Intermolecular Forces

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  • Intermolecular Forces
    • London Dispersion Forces
      • Electrons are constantly moving around the nucleus and can align at one side of the nucleus at times
        • When this happens, a partial positive and partial negative side of the atom arises
          • The weak attraction between the partial positive and partial negative side of two atoms is known as a London Dispersion Force
      • These forces are the weakest of the three types of inter-molecular force
      • London dispersion forces can be found in all molecules, but non-polar molecules are the only molecules which have no other force acting between their molecules
        • We can say that non-polar molecules are likely to have low melting and boiling points as London Dispersion Forces are easily broken by small amounts of energy
    • Dipole-Dipole Interactions
      • Different elements have different values of electro-negativity
        • In molecules, one element will have a partial positive charge and one a partial negative charge
          • The force found between the partial positive and partial negative of two molecules is known as a Dipole-Dipole Interaction
      • These interactions are slightly stronger than London Dispersion Forces but a lot weaker than Hydrogen bonding
      • Dipole-Dipole Interactions can be found only in polar molecules
        • Use the trick: Polar bears live at the north and south pole
    • Hydrogen Bonding
      • Hydrogen Bonding can be found between hydrogen and either fluorine, nitrogen or oxygen
        • The most common example of hydrogen bonding is in water molecules or molecules which have hydroxyl groups
        • Use rhyme: Hydrogen Bonding is FON (like fun but fon for the elements:))
      • Hydrogen Bonding is the strongest form of inter-molecular force
        • We can say that molecules with hydrogen bonding have high melting and boiling points as the inter-molecular forces require a lot of energy to break them

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