Intermolecular Forces & Physical Properties

Description - London Dispersion

Weak forces that result from temporary shifts in density of electrons in electron clouds.

Description - Dipole-Dipole

Attractions between oppositely charged regions of polar molecules.

Description - Hydrogen Bonding

Special dipole-dipole attractions that occur between molecules containing a hydrogen atom covalently bonded to a small, highly electronegative atom (N, O, F) and the lone pair of electrons on another molecule containing N, O, or F.

Description - Ion-Dipole

The result of an electrostatic interaction between a charged ion and a molecule that has a dipole.

Strength - London Dispersion

Greater attraction results as the size of the molecule or atom increases. This is due to greater polarizability of the electron cloud.

Strength - Dipole - Dipole

For small molecules, this intermolecular force is stronger than dispersion forces.

Strength - Hydrogen Bonding

Stronger than dispersion and dipoledipole forces due to the large electronegativity difference in the bonds and small size of the hydrogen atom.

Strength - Ion-Dipole

It is an attractive force that is commonly found in ionic compounds dissolved in polar liquids.

Example - London Dispersion

H2

Example - Dipole-Dipole

Hydrochloric acid, HCl

Example - Hydrogen Bonding

Hydrofluoric acid, HF

Example - Ion-Dipole

Sodium chloride (NaCl) dissolved in water.

Intermolecular forces

Forces of attraction and repulsion between molecules

Intramolecular forces

Forces between atoms (bonds)

Forces between substrate & enzyme

dipole-dipole

Forces that cause a protein to fold

dipole-dipole attraction and nonpolar-dipole repulsion

Miscible

forming a homogeneous mixture when added together (dissolving evenly)

Immiscible

liquids that do not form a homogenous mixture when added together (do not mix)

Nonpolar solutes are soluble in

nonpolar solvents

Polar solutes are soluble in

polar solvents

Ions are soluble in

polar solvents

"Like dissolves like"

Substances with charges (dipoles & ions) dissolve in other substances with charges. Substances without charges (nonpolar) dissolve in substances without charges.

Boiling point definition

Boiling point is the temperature at which a substance changes from liquid to gas at standard pressure.

Boiling point and intermolecular forces

Substances with higher boiling points have stronger intermolecular forces

Freezing point definition

the temperature at which a liquid turns into a solid when cooled.

Freezing point and intermolecular forces

Substances with higher freezing points have stronger intermolecular forces

Surface tension definition

the attractive forces between particles on the surface of a substance that tend to be arranged in a shape with the least surface area.

Surface tension and intermolecular forces

Higher surface tension requires stronger intermolecular forces

Capillary action

the tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension.

Vapor pressure definition

the pressure exerted by a vapor on the surface of a liquid.

Vapor pressure and intermolecular forces

Lower vapor pressure requires stronger intermolecular forces

Stronger London Dispersion forces

More electrons, larger electron cloud, larger molecule or atom