2C - Intermolecular forces

     1)    Describe how Van der Waals' forces arise. [6]

                 Electrons in shells are continually moving [1]   the electrons are continually fluctuating [1]

            this creates an uneven distribution of electrons [1]  which sets up an instantaneous dipole [1]

            this induces a dipole in neighbouring atoms / molecules [1]  creating weak forces of attraction [1]

     2)    Arrange the elements of Group 0 in order of increasing boiling points.  Explain your answer.  [4]

            He, Ne, Ar, Kr, Xe, Rn  [1]  As you go down the Group, the atoms have more electrons [1]

            which gives a greater uneven distribution of electrons [1] 

            giving stronger instantaneous dipole - induced dipole forces of attraction [1]

     3)    Which of the following have hydrogen bonding:  [6]

     4)    Draw diagrams of hydrogen bonding between the following molecules.  Include any dipoles:

            a)  2 molecules of water  [2]     Labelled bond between LP and H [1] Dipoles shown [1]

            b)  2 Molecules of ammonia  [2] 

                 Labelled bond between LP and H between the 2 molecules [1] Dipoles shown [1]

            c)  1 molecule of water and 1 molecule of ammonia  [2]

                              Labelled bond between LP and H [1] Dipoles shown [1]

    5)    State 3 anomalous properties of water and explain each property:  [6]

Unusually high melting / boiling point  [1] H bonding is strongest IMF, more energy needed to overcome  [1]

Ice less dense than water  [1] H bonds are longer than covalent bonds  [1]

Surface tension  [1]  extensive H bonds across the surface of water  [1]