CHEM 101 Lecture Notes - Lecture 35: London Dispersion Force, Intermolecular Force, Chemical Polarity

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CHEM 101-Lecture 35-Intermolecular Forces
States of matter
The state of a substance is dependant on two factors:
1. The kinetic energy of the molecules, which separates molecules
2. The intermolecular forces, which pull molecules together
In gases, the kinetic energy is greater than the intermolecular forces, and the molecules
are far apart and do not interact significantly (disordered)
In liquids, the intermolecular forces are strong enough to keep the molecules in contact,
but their kinetic energy allows them to move past each other
In solids, the intermolecular forces are greater than the kinetic energy, and the
molecules are held in place (ordered)
Intermolecular forces
Intermolecular forces are forces which act between two molecules
Intermolecular forces are much weaker than intramolecular forces (forces within a
molecule)
Intermolecular forces affect the physical properties of a substance (melting point, boiling
point, vapour pressure, viscosity, etc.)
The types of intermolecular forces are ion-dipole forces, dipole-dipole forces, hydrogen
bonding, and London dispersion forces
Ion-dipole forces
An attraction between a partial charge on a polar molecule and an oppositely charged
ion
Cations are attracted to δ- charges, and anions are attracted to δ+ charges
These intermolecular forces are responsible for the dissolution of ionic compounds in
polar solvents (ex: table salt dissolving in water)
Sodium chloride dissolving in water
http://forestchemistry.weebly.com/unit-15---intermolecular-forces--bonding.html
Dipole-dipole forces
An attraction between a partial negative charge on one polar molecule and a partial
positive charge on another
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