Intermolecular Forces - van der Waals forces (sometimes the...

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Intermolecular Forces Intermolecular forces are generally much weaker than covalent bonds Only 16 kJ/mol of energy is required to overcome the intermolecular attraction between HCl molecules in the liquid state (i.e. the energy required to vaporize the sample) However, 431 kJ/mol of energy is required to break the covalent bond between the H and Cl atoms in the HCl molecule Thus, when a molecular substance changes states the atoms within the molecule are unchanged The temperature at which a liquid boils reflects the kinetic energy needed to overcome the attractive intermolecular forces (likewise, the temperature at which a solid melts). Thus, the strength of the intermolecular forces determines the physical properties of the substance Attractive forces between neutral molecules Dipole-dipole forces London dispersion forces Hydrogen bonding forces Typically, dipole-dipole and dispersion forces are grouped together and termed
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Unformatted text preview: van der Waals forces (sometimes the hydrogen bonding forces are also included with this group) Attractive forces between neutral and charged (ionic) molecules ion-dipole forces Note that all of these forces will be electrostatic in nature Ion-dipole Involves an interaction between a charged ion and a polar molecule (i.e. a molecule with a dipole ) Cations are attracted to the negative end of a dipole Anions are attracted to the positive end of a dipole The magnitude of the interaction energy depends upon the charge of the ion ( Q ), the dipole moment of the molecule ( u ) and the distance ( d ) from the center of the ion to the midpoint of the dipole Ion-dipole forces are important in solutions of ionic substances in polar solvents (e.g. a salt in aqueous solvent)...
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This note was uploaded on 11/22/2011 for the course CHEMISTRY CHM1025 taught by Professor Laurachoudry during the Fall '10 term at Broward College.

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Intermolecular Forces - van der Waals forces (sometimes the...

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