Chemistry

London Forces


This intermolecular interaction may also be called dipole-induced or Van der Waals forces.

It is the weakest interaction of all and occurs in nonpolar molecules. In this case, there is no electrical attraction between these molecules.

They should always remain isolated and that is what really happens, because at room temperature they are in the gaseous state.

They are about ten times weaker than dipole-dipole bonds.

The molecule, even though it is nonpolar, has many rapidly moving electrons. It may happen at any given moment that a molecule has more electrons on one side than on the other.

This molecule will therefore be momentarily polarized and, by electric induction, will cause the polarization of a neighboring molecule (induced dipole), resulting in a weak attraction between them. This attraction is the London force.

Examples: Cl2, CO2, H2

Summary table of physical properties and connection types

Substance Type

Metallic

Ionic

Polar covalent

Covalent apolar

Particle

Atoms and Cations

Ions

Molecules

Molecules

Attraction between particles

By "free electrons"

Electrostatic attraction

Hydrogen or dipole-dipole bridges

Van der waals

Physical state

Solid (except Hg)

Solid

Liquid

Gaseous

PF and PE

High

High

Low

Very low

Electric conductivity

High (solid and liquid) without attracting substance

High (cast or in solution)

Virtually null when pure. Conductive when in solution

Null

Solubility in common solvents

Insoluble

Polar solvent soluble

Polar solvent soluble

Non-solvent solvent soluble

Toughness

Hard but malleable and ductile

Hard but brittle

-

-

Generally, the rule that similar dissolves similar is used. This means that polar solvent dissolves polar substance and apolar solvent dissolves apolar substance.

But this rule is not always correct. Water, for example, is a polar substance and can dissolve ethyl alcohol, which is nonpolar.