Intermolecular strength refers to the forces of attraction between molecules. These forces can be either weak or strong and are responsible for the physical properties of a substance, such as boiling point, melting point, and viscosity.
Intramolecular strength refers to the forces of attraction within a molecule, such as covalent bonds. These forces are much stronger than intermolecular forces, which only exist between separate molecules.
The main types of intermolecular forces are London dispersion forces, dipole-dipole interactions, and hydrogen bonding. London dispersion forces are the weakest and occur between all molecules. Dipole-dipole interactions occur between polar molecules, and hydrogen bonding is a special type of dipole-dipole interaction that occurs between molecules containing hydrogen bonded to a highly electronegative atom.
The strength of intermolecular forces determines the physical properties of a substance. For example, substances with strong intermolecular forces, such as water, have high boiling points and are liquid at room temperature. On the other hand, substances with weak intermolecular forces, such as methane, have low boiling points and are gases at room temperature.
Intermolecular forces can be manipulated by changing the molecular structure of a substance. For example, increasing the length of carbon chains in a hydrocarbon molecule can increase the strength of London dispersion forces. Introducing polar functional groups can also increase the strength of dipole-dipole interactions.