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Intermolecular Forces

Intermolecular Forces. 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

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Intermolecular Forces

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  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. H2O 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 > C12H22O11 > H2O • iron > salt > sugar > ice

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