Chapter 12

intramolecular - forces that hold the molecule together, like covalent bonds.

intermolecular - attractive forces that hold molecules/atoms/ions to each other in condensed phases (liquid and solid). weaker than intramolecular forces. all attractive forces between neutral atoms and molecules called van der Waals forces.

types of van der Waals forces:

#1 dispersion forces - result from the Coulombic attractions between instantaneous dipoles of non-polar molecules, fleeting charge separations or the movement of electrons. magnitude depends on how mobility of electrons; instantaneous or induced.

#2 dipole-dipole attractions - attractive forces between polar molecules. magnitude of attractive forces depends on magnitude of dipole (how polar the bond is). as the dipole increases, so does the attractive force, resulting in higher melting and boiling points.

#3 hydrogen bonding - special type of dipole-dipole interaction that only occurs in molecules with H bonded to a small, highly electronegative atom like N, O, F. within a group, teh boiling point increases with mass UNLESS H-bonding adds more attractive forces.

when a substance has each IMF - all molecules, even nonpolar ones, exhibit dispersion forces, polar molecules (w/ polar bonds not cancelled by symmetry) exhibit dipole-dipole attractions plus dispersion forces, and polar molecules with N-H, F-H, or O-H bonds exhibit hydrogen bonding, plus dipole-dipole attraction, and dispersion forces.

surface tension - tendency of liquids to minimize their surface area giving rise to a membrane-like surface, increases as intermolecular forces increase.

viscosity - measure of a liquid’s resistance to flow (free flowing = low viscosity, heat lowers viscosity) increases as intermolecular forces increases.

cohesive forces - intermolecular attractive forces between identical molecules of a substance (causes water droplets to form and water to have a “tough” surface).

adhesive forces - intermolecular attractive forces between different molecules (water creeps up the side of a glass tube forming a meniscus that is concave).

capillary action - ability of a liquid to flow against gravity, up an arrow tube to to adhesive and cohesive forces.

phase changes - a phase is a homogenous part of a system that is separated from the rest of the system by a well defined boundary. when a substance goes from one phase to another phase, it has undergone a phase change:

  • freezing of water: liquid to solid

  • melting of ice: solid to liquid

  • evaporation/vaporization of water: liquid to gas

  • condensation of water vapor: gas to liquid

  • sublimation of dry ice: solid to gas

  • deposition of iodine: gas to solid