Intermolecular Forces

Ion-Dipole

The electrostatic interaction between a charged ion and a neutral molecule that has a dipole

Most commonly found in solutions

Attraction becomes stronger as either the charge on the ion increases, or as the magnitude of the dipole of the polar molecule increases

In this example, the oxygen atom in the water molecule has a slightly negative charge and is attracted to the positive sodium ion.

Dipole-Dipole

The force of attraction between the slightly positive end of one polar molecule and the slightly negative end of an adjacent polar molecule

Occurs between neutral polar molecules

Weaker than ion-dipole forces

Increase with an increase in the polarity of the molecule

Only has a significant effect when the molecules involved are close together

In this example, the partial negative charge of the chlorine atom attracts to the partial positive charge of the hydrogen atom of the other compound.

If the dipoles of a molecule cancel each other out, then the molecule is non-polar and symmetrical. If not, then the molecule is polar and asymmetrical

Induced Dipole-Dipole

The force of attraction that forms when a polar molecule induces a dipole in a non-polar molecule by disturbing the arrangement of electrons

A weak form of attraction

In this example, the water molecule (polar) induces a dipole into the oxygen molecule (non-polar) which results in a weak attraction between the two.

Hydrogen Bonding

The force of attraction between a hydrogen atom attached to a highly electronegative atom (N, O, or F) and a highly electronegative atom in another molecule

Dipole-dipole interaction

Positive charge is attracted to the negative charge of an electronegative atom in a nearby molecule

Stronger than dipole-dipole or dispersion forces

Important in the organization of biological molecules

In this example, the partially negative oxygen atom in one of the water molecules is attracted to the partially positive hydrogen atom in another nearby water molecule

London Dispersion

The force of attraction acting between all entities, including polar molecules, non-polar molecules and unbonded atoms, caused by the temporary imbalance of electrons within the entities

Temporary dipole induces a dipole into neighboring molecules

Weakest intermolecular force

The greater the polarizability, the stronger the dispersion forces

Larger the molecule, the greater the polarizability

In this example, the uneven distribution of electrons in the He atom (left) causes a temporary dipole (middle). This induces a dipole in the neighboring He atom (right).

The set of attractive and repulsive forces that occur between molecules

They strength of the intermolecular forces determines the following physical properties of molecular compounds:

Physical state of a compound at a specific temperature and pressure

Melting Point

Boiling Point

Surface Tension

Hardness and Texture

Solubility in various solvents