1. Intermolecular Forces

2. Dispersion or London Forces Weakest intermolecular force Constant motion of electrons may lead to uneven distribution of electrons at any particular moment: –“temporary dipole” which may induce a dipole in nearby molecule. Acts on all molecules all the time Only intermolecular force acting among noble gas atoms and nonpolar molecules http://www.chem.unsw.edu.au/coursenotes/CHEM1/nonunipass/HainesIMF/dispersion.html

3. Dipole Force Attraction between two polar molecules: (-) end of one polar molecule attracts the (+) end of another polar molecule More polar  stronger dipole force Closer together  stronger dipole force

4. Hydrogen Bonding Special type of dipole bond Always involves H Usually involves O, F or N (small, high electronegativity) Strongest intermolecular force How strong? 5% of the strength of a covalent bond Results in higher b.p. and high viscosity e.g. H 2 O http://myhome.sunyocc.edu/~weiskirl/water.htm

5. Comparing All Bond Types Which is stronger? metallic > ionic > covalent > H bond > other dipole > dispersion e.g. Compare melting points: Fe > NaCl > C 12 H 22 O11 > H 2 O iron > salt > sugar > ice