Intermolecular Forces of Attraction AP Chemistry 2 SNSH Spring 2000

Kinetic Molecular Theory 4 All matter is composed of atoms that are in constant motion

Kinetic Theory Facts 4 All phases of matter express the degree that they reflect the kinetic theory through their kinetic energy 4 kinetic energy is measured by temperature 4 phase changes involve changes in temperature due to the existence threshold temperature of each phase (i.e. ice naturally is found at cold not hot temperatures)

4 While gases have a great deal of random motion, solids and liquids exist at lower temperatures, thus allowing other forces of attraction to act upon them 4 these forces are the van der Waals forces

Definitions 4 Bonds are intramolecular forces of attraction 4 Forces of attraction between molecules are called intermolecular forces of attraction 4 intermolecular forces of attraction are commonly called van der Waals forces

The Condensed Phases 4 Solids and Liquids 4 Physical properties of the condensed phases reflect the degree of intermolecular forces (i.e. boiling point)

Dipole-dipole forces 4 Exist between neutral polar molecules 4 work best the closer the molecules are to each other 4 the greater the polarity of the molecules, the greater the force of attraction

H bonding 4 Special case of dipole-dipole interaction specifically between H of one polar molecule with N, O or F and an unshared electron pair of another nearby small electronegative ion (usually N, O, or F on another molecule) 4 VERY STRONG

London dispersion forces 4 Induced dipoles 4 not really dipoles on the AVERAGE, but instantaneously dipole conditions can exist thus allowing for pseudopolar regions to occur

4 No matter how strong the van der Waal force of attraction is, it is still not stronger than attractions involving ions

Ion-dipole forces 4 Attraction between ions and the partial charge on the end of a polar molecule 4 ex. NaCl in water solution