Inter & Intramolecular Forces (Cambridge (CIE) AS Chemistry): Revision Note

Comparing Bonds & Intermolecular Forces

Intramolecular forces

• Intramolecular forces are forces within a molecule

• Ionic bonding is the electrostatic attraction between positive (cations) and negative (anions) ions in an ionic crystal lattice

  • These ions are formed by transferring the electrons from one species to the other

• Covalent bonds are formed when the outer electrons of two atoms are shared

• Metallic bonding is the electrostatic attraction of positively charged metal ions and their delocalised electrons in a metal lattice

Intramolecular forces

The three types of intramolecular forces are ionic, covalent and metallic bonding

Intermolecular forces

• Intermolecular forces are forces between molecules and are also called van der Waals’ forces

• Permanent dipole - permanent dipole are the attractive forces between two neighbouring molecules with a permanent dipole

• Hydrogen bonds are a special type of permanent dipole - permanent dipole forces

• Instantaneous dipole - induced dipole (London dispersion) forces are the attractive forces between a temporary dipole and a neighbouring molecule with an induced dipole

Permanent dipoles as intermolecular forces

Permanent dipole - permanent dipole are the intermolecular forces that occur between two neighbouring molecules with a permanent dipole

Instantaneous dipoles as intermolecular forces

Instantaneous dipole - induced dipole (London dispersion) forces are the intermolecular forces that occur between a temporary dipole and a neighbouring molecule with an induced dipole

Hydrogen bonding as an intermolecular force

Hydrogen bonds are a special type of permanent dipole - permanent dipole forces

• In general, intramolecular forces are stronger than intermolecular forces

• The strengths of the types of bond or force are as follows:

The varying strengths of different types of bonds

In general, ionic bonding is the strongest force while instantaneous dipole - induced dipole is the weakest force