Intermolecular Forces Essay

8818 Words Nov 3rd, 2011 36 Pages
Oakland Schools Chemistry Resource Unit

Intermolecular Forces
Brook R. Kirouac David A. Consiglio, Jr. Southfield‐Lathrup High School Southfield Public Schools

Bonding: Intermolecular Forces
Content Statements:

C2.2: Chemical Potential Energy Potential energy is stored whenever work must be done to change the distance between two objects. The attraction between the two objects may be gravitational, electrostatic, magnetic, or strong force. Chemical potential energy is the result of electrostatic attractions between atoms. C3.3: Heating Impacts Heating increases the kinetic (translational, rotational, and vibrational) energy of the atoms composing elements and the molecules or ions composing compounds. As the kinetic
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Hydrogen bonding exists only in molecules with an N-H, O-H, or F-H bond. Dipole-Dipole: Dipole-dipole interaction is the attraction between a partially negative portion of one molecule and a partially positive portion of a nearby molecule. Dipole-dipole interaction occurs in any polar molecule as determined by molecular geometry.

Dipole-Dipole Interaction

www.lbl.gov/images/MicroWorlds/H2OH-bond.gif

Hydrogen Bonding (unusually strong Dipole-Dipole)

London Dispersion: London dispersion forces result from instantaneous nonpermanent dipoles created by random electron motion. London dispersion forces are present in all molecules and are directly proportional to molecular size. Effects of Intermolecular Forces: The strength of intermolecular forces present in a substance is related to the boiling point and melting point of the substance. Stronger intermolecular forces cause higher melting and boiling points. EXAMPLES: CH4 - Methane: has only very weak London dispersion forces (lowest b.p. & m.p.) CHCl3 - Chloroform: has dipole-dipole interaction (moderate b.p. & m.p.) NH3 - Ammonia: has hydrogen bonding and dipole-dipole interaction (high b.p. & m.p.)

The Forces between Molecules All matter is held together by force. The force between atoms within a molecule is a chemical or intramolecular force. The force between molecules is a

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