CHEM 123N Lecture Notes - Lecture 2: London Dispersion Force, Intermolecular Force, Polarizability

• School: Old Dominion University
• Department: Chemistry And Biochemistry
• Course: CHEM 123N
• Professor: John Donat

Document Summary

Intra - force reflected in physical properties of a substance. If two polar molecules have comparable mw, shape, then dipole dipole forces likely dominate. If one molecule has greater mw than another, then dispersion forces likely determine its physical properties. Nonpolar particles can become instantaneously and temporarily polarized to form dispersion force, considered an (cid:718)induced dipole(cid:719). Polarizability - the tendency of an electron cloud to distort. Molecular weight determines the magnitude of a dispersion force. Small molecules = less polarizable = weaker force, the opposite being true as well. Longer molecules have a greater surface area and greater dispersion forces. Dipole-dipole forces (collectively (cid:718)van der waals(cid:719) forces) These are only significant if the molecules are in close contact. This is amolecule with hydrogen bonded to no or f. H atom bonded to a highly electronegative atom, and an electron pair on an electronegative atom in an adjacent molecule or chemical group.