Intermolecular forces

Intermolecular Forces Overview

• Intermolecular forces are the forces of attraction between molecules, which are weaker than the strong covalent bonds within a molecule.
• They determine the state of matter (solid, liquid, or gas), boiling and melting points, and solubility.

Types of Intermolecular Forces

• Dispersion Forces (Van der Waals Forces): These are the weakest type of forces caused by temporary fluctuations in electron distributions. They exist in all molecules, with the strength increasing with the size and shape of molecule.
• Dipole-Dipole Forces: These are stronger than dispersion forces and occur between polar molecules with permanent dipoles, which have positive and negative ends due to uneven distribution of electrons.
• Hydrogen Bonding: This is the strongest type of intermolecular force and occurs between hydrogen and highly electronegative atoms (F, O, N). It gives water its unusual properties, such as high boiling point.

Impact on Boiling and Melting Points

• Substances with weak intermolecular forces usually have lower melting and boiling points due to less energy required to overcome these forces and change the state of matter.
• Conversely, substances with strong intermolecular forces usually have higher melting and boiling points.

Solubility and Intermolecular Forces

• Solubility depends on the ability of a solvent to break intermolecular forces in the solute.
• Polar solvents, like water, dissolve polar solutes (like sugar) well due to dipole-dipole interaction or hydrogen bonding.
• Non-polar solvents are good at dissolving non-polar solutes due to dispersion forces.

The Role of Intermolecular Forces in Real-Life Applications

• The variation in intermolecular forces can explain the vast differences in natural and artificial substances’ properties, including polymers, oils, and cleaning products.
• For instance, soaps and detergents can dissolve in water and grease due to having both polar and non-polar areas aligned with respective substances.