CHEM 11A Lecture 20: CHEM11achapter11

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The state in which matter exists depends on the strength of the forces of attraction between molecules relative to the amount of thermal energy in the sample. The macroscopic physical properties of liquids and solids are determined by the intermolecular forces that hold them together at the microscopic level. Intermolecular forces are the result of electrostatic interactions between charges permanent and symmetrical (ions) partial (polar molecules) temporary. If q1 and q2 are opposite in sign (+/-), potential energy (e) decreases as the separation between the charges (r) decreases. If q1 and q2 are the same sign (+/+ or -/-), potential energy (e) increases as the separation between the charges (r) decreases. Even the strongest intermolecular forces are much weaker than the intramolecular forces that comprise chemical bonds between atoms. Intermolecular forces smaller charges interacting at greater distances. Intramolecular forces (chemical bonds) large charges interacting at very close distances. Present between all particles in the condensed phases.