Ideal Gas Law

Section 1: Overview of Intermolecular Forces

Intermolecular forces are forces of attraction between molecules. They are weaker than the forces within molecules, known as intramolecular forces.
These forces dictate the physical properties of substances like boiling and melting points, viscosity, and surface tension.
There are three types of intermolecular forces: London Dispersion Forces, Dipole-Dipole Interactions, and Hydrogen Bonding.

Section 2: London Dispersion Forces

London Dispersion Forces (also known as Van der Waals forces) are present between all atoms and molecules regardless of polarity.
These forces are the result of instantaneous dipoles caused by the movement of electrons.
The strength of London Dispersion Forces increases with the increase in size and shape of the molecule.

Section 3: Dipole-Dipole Interactions

Dipole-Dipole Interactions are present between polar molecules, i.e., molecules having a net dipole moment.
In these interactions, the positive end of one molecule attracts the negative end of another molecule.
Boiling points of molecules with dipole-dipole forces are higher than those with only London Dispersion Forces, all else being equal.

Section 4: Hydrogen Bonding

Hydrogen Bonding is a special type of dipole-dipole interaction occurring between a hydrogen atom and highly electronegative atoms like oxygen, nitrogen, or fluorine.
It’s the strongest type among the three intermolecular forces.
Hydrogen bonding is responsible for the unusual behaviour in water such as its high boiling point relative to its molecular weight.

Section 5: Properties Based on Intermolecular Forces

Intermolecular forces influence properties like volatility, viscosity, and surface tension.
Substances with strong intermolecular forces have higher boiling points and are less volatile as more energy is required to overcome these forces.
Viscosity is the measure of a fluid’s resistance to flow. Higher intermolecular forces result in higher viscosity.
Surface tension is the force that keeps a liquid together, making it droplet-like. It increases with the increase in intermolecular forces.