Intermolecular forces

Intermolecular Forces Forces that occur between molecules. Intramolecular (ionic and covalent) bonds are stronger than intermolecular forces.

Intermolecular Forces There are four kinds of intermolecular forces. Dipole–dipole forces (between polar molecules) Hydrogen bonding (between H of one polar molecule and O, N, F of another polar molecule) Ion-Dipole Forces (between ions and molecules) London dispersion forces (between nonpolar molecules)

Dipole–Dipole Attraction Polar molecules contain different atoms which have different electronegativities. Oppositely charged ends attract and like ends repel. Molecules organize themselves maximizing the attractive forces and minimize repulsive forces

Hydrogen Bonding Strong dipole-dipole forces. Hydrogen is bound to a highly electronegative atom – nitrogen, oxygen, or fluorine. Blue dotted lines are the intermolecular forces between the water molecules.

Hydrogen Bonding Affects physical properties Boiling point

London Dispersion Forces Instantaneous dipole in a given atom induces a similar dipole in a neighboring atom. Significant in large atoms/molecules. Occurs in all molecules, including nonpolar ones.

Ion Dipole Forces They are typically found in aqueous solutions of ionic compounds (salt water) Nonbonding electrons found on the oxygen atom are strongly attracted to the sodium ion.

Overview of intermolecular Forces Type of Force Relative Strength Present in Examples Dispersion Force (London Force) Weak, increasing with size atoms/molecules H2 (g) Polar molecules HCl Dipole-dipole force moderate Molecules with hydrogen bonded to N,O, or F Hydrogen bond Strong HF, NH3, H2O Ion-dipole Very strong Mixtures of ionic and polar compounds Na+,Cl-, and H2O