2.2 Intermolecular Forces

What is the difference between Intramolecular Bonds and Intermolecular Bonds? Simply define 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

What are the types of Intermolecular Bonds? What are they collectively known as?

1. London forces

2. Dipole-dipole forces

3. Hydrogen bonds

Collectively known as Van der Waals forces

Tell me about 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

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

Connect what you know about London Forces to Methane and Octane

Since methane’s molecules are small, it is a gas at room temperature. Whereas octane’s molecules are large meaning the forces accumulate rendering octane a liquid.

Tell me about 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

Tell me about 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

Compare and Contrast

Intramolecular Bonds	Intermolecular Forces
Holds one molecule together	Holds many molecules together
Strong attraction between atoms	Weak attraction between molecules
Commonly called “bonds”	Known as van der waals forces
Determines if electrons are transferred or shared	Determines state of substance
Ex: Ionic, covalent, polar covalent	Ex: London forces, dipole-dipole, hydrogen bonds