2.2 Intermolecular Forces

Intermolecular Bonds

Intramolecular bonds- hold atoms in a molecule together

Intermolecular Bonds - hold two or more molecules together

much weaker and determine physical state of substance

Three types of intermolecular bonds:

1. London forces

2. Dipole-dipole forces

3. Hydrogen bonds

Collectively known as Van der Waals forces

London Forces

bonds that are formed due to a temporary unequal distribution of electrons in an atom

Very weak, occur between small nonpolar molecules (ex: methane)

Each molecule is weakly attracted to its neighbour

That is why methane is a gas at room temperature

CH4

Cumulative effect of London forces become more significant in large nonpolar molecules (ex: octane)

In larger molecules, many weak attractive forces result in a closer association

As a result, octane is a liquid at room temperature

C8H18

Dipole-Dipole Forces

occur between polar molecules, like HCl

Slightly positive end of one polar molecule is attracted to slightly negative end of another polar molecule

Stronger than London forces

Hydrogen Bonds

dipole-dipole forces that form between electropositive H of one polar molecule and an electronegative N, O, or F of another

Strongest intermolecular force

Summary