Intermolecular Forces
Intermolecular forces (IMFs) are forces of attraction or repulsion between molecules. They are weaker than intramolecular forces (bonds within a molecule) but play a crucial role in determining physical properties such as boiling point, melting point, solubility, and vapor pressure.
Types of Intermolecular Forces
-
London Dispersion Forces (Van der Waals)
- Present in all molecules, especially nonpolar.
- Caused by temporary dipoles due to electron motion.
- Strength increases with molecular size and polarizability.
-
Dipole-Dipole Interactions
- Occur in polar molecules with permanent dipoles.
- Positive end of one molecule attracts the negative end of another.
-
Hydrogen Bonding
- Special case of dipole-dipole.
- Occurs when hydrogen is covalently bonded to highly electronegative atoms (N, O, F) and attracted to lone pairs on another molecule.
- Responsible for water’s high boiling point and unique properties.
-
Ion-Dipole Interactions
- Occur between ions and polar molecules.
- Important in solutions where ionic compounds dissolve in polar solvents like water.
Importance
- Boiling and Melting Points: Stronger IMFs require more energy to overcome.
- Solubility: “Like dissolves like” depends on similar types of IMFs.
- Physical Properties: Vapor pressure, surface tension, and viscosity are influenced by IMFs.
Examples
- Water (H₂O): Hydrogen bonding dominates, leading to high boiling point.
- Iodine (I₂): Nonpolar, London dispersion forces dominate.
- NaCl in water: Ion-dipole interactions allow solubility.
Have Questions?
If you have any questions, or are looking for more resources, you can join our Discord Server