HS Chemistry Unit 2 - Intermolecular Forces

Intermolecular force

Force between separate molecules; weaker than intramolecular force, determines physical properties such as boiling point and vapor pressure

Intramolecular force

Force within a single molecule; stronger than intermolecular force

Note: This is because two atoms differ in electronegativity, and this will create a partial negative charge on one molecule and a partial positive charge on the other

Polar covalent bond

Covalent bond in which electrons are shared unequally between atoms because they differ in electronegativity

Nonpolar covalent bond

Covalenrt bond in which electrons are shared equally or almost equally between atoms with the same or similar electronegativities

Polar molecule

A molecule with uneven distribution of charge, so one side is partially positive and the other is partially negative (a dipole)

Nonpolar molecule

A molecule with even distribution of charge and a symmetrical shape, its bonds are nonpolar, or its polar bonds cancel due to symmetry

(London) Dispersion force

• a weak, temporary force that is caused by momentary shifts in electron distribution and exists between all molecules

• the only intermolecular force between nonpolar molecules

• gets stronger as molecules get larger

dipole-dipole force

a force between the partial positive end of one polar molecule and the partial negative end of the other molecule

Hydrogen bond

partially strong dipole-dipole bond between a hydrogen atom and a nitrogen, oxygen, or fluorine atom

Vapor pressure

pressure exerted by the vapor of a liquid when the vapor is in equilibrium at a given temperature, decreases as intermolecular force increases

Boiling point

The temperature at which a liquid’s vapor pressure is equal to external pressure acting on the liquid, so the liquid changes to a gas throughout; increases as intermolecular force increases

Normal boiling point

The temperature at which a liquid boils when the external pressure is equal to 1 atm (standard atomic pressure)

Surface tension

An elastic-like force on the surface of a liquid caused by the attraction of its molecules

Electronegativity

The measure of an atom’s tendency to attract shared electrons