Intermolecular forces

Definition

Intermolecular forces are the forces of attraction and repulsion between molecules that influence the physical properties of substances. These forces are weaker than intramolecular forces, which hold atoms together within a molecule.

5 Must Know Facts For Your Next Test

1. There are three main types of intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonds.
2. London dispersion forces are present in all molecules, whether polar or nonpolar, and increase with molecular size.
3. Dipole-dipole interactions occur between molecules that have permanent dipoles, meaning they have regions of partial positive and negative charge.
4. Hydrogen bonds are a special type of dipole-dipole interaction that occur when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine.
5. Intermolecular forces significantly influence boiling points, melting points, vapor pressures, and viscosities of substances.

Review Questions

• What are the three main types of intermolecular forces?
• How do London dispersion forces differ from dipole-dipole interactions?
• Why do hydrogen bonds only form with certain elements like oxygen, nitrogen, or fluorine?

Related terms

London Dispersion Forces:

Weak intermolecular attractions arising from temporary shifts in electron density that create instantaneous dipoles in molecules.

Dipole-Dipole Interactions:

Attractions between oppositely charged regions of polar molecules that have permanent dipoles.

Hydrogen Bonding:

A strong type of dipole-dipole interaction occurring between hydrogen atoms bonded to highly electronegative atoms like O, N, or F and a lone pair on another electronegative atom.