Intermolecular Force

Intramolecular forces are forces within a molecule, ad intermolecular forces are forces between molecules.

For example, intermolecular force is the attraction force between hydrochloric acid, and intramolecular force is the force between hydrogen and chlorine acids.

Figure 1: Intermolecular attraction and intramolecular attraction

Dipole-Dipole

• Dipole–dipole forces (or attractions) only exist between polar molecules that have a permanent dipole, and this permanent dipole arises due to the difference in electronegativity between atoms

London dispersion forces

• London dispersion forces consist of temporary or instantaneous dipoles and induced dipoles
• A temporary dipole is caused by changes in electron density within an atom or molecule. 
• In general, as the molar mass of a molecule increases, so does its polarisability. This results in a larger temporary or induced dipole being formed within the molecule, which leads to stronger London dispersion forces between the molecules. 
• London dispersion forces exist between all molecules and atoms. 

Hydrogen Bonding

• Hydrogen bonding occurs between molecules that have an electronegative nitrogen, oxygen or fluorine atom directly bonded to a hydrogen atom.
• It is often described as a stronger type of dipole–dipole attraction that is responsible for the high boiling point of water (H₂O)

• hydrogen bonding is considered to be the strongest, followed by dipole–dipole attractions and finally London dispersion forces, which are considered to be the weakest.  
• hydrogen bonding > dipole–dipole forces  > London dispersion forces

• Intermolecular forces quiz 1

References