Intermolecular Bonding

Intermolecular bonds are the forces between molecules, which hold them together in a substance.
These forces are weaker than both ionic bonds (between cations and anions) and covalent bonds (shared pair of electrons between atoms).
There are three main types of intermolecular forces: dipole-dipole forces, London dispersion forces, and hydrogen bonding.
Dipole-dipole forces happen when the positive end of a molecule is attracted to the negative end of another.
They occur only in polar molecules, which have a difference in electronegativity between the bonded atoms.
The second type, London dispersion forces, also known as Van der Waals forces, are present in all molecules, polar and non-polar.
These forces occur due to temporary shifts in the electron clouds of atoms, creating temporary positive and negative regions, which create attractions between molecules.
The strength of London dispersion forces increases with larger molecules, as they have more electrons and a larger electron cloud.
Hydrogen bonds are the strongest type of intermolecular force and occur when a hydrogen atom bonded to a highly electronegative atom is attracted to a lone pair of electrons on another highly electronegative atom.
These commonly occur with nitrogen, oxygen, and fluorine atoms as they are the most electronegative elements.
The unique properties of many substances like water and DNA can be attributed to their hydrogen bonding. Water’s high boiling and melting points for a molecule of its size, and its ability to dissolve many substances, are due to its hydrogen bonds.
In terms of boiling and melting points, stronger intermolecular forces mean higher temperatures are required to break the bonds. Hence substances with strong intermolecular forces have high boiling and melting points.
When considering the properties of a substance, remember to consider both the type of atomic bonding and the intermolecular forces at play.