Chemistry - Intermolecular and Intramolecular Forces

Intramolecular forces

Forces that act within a molecule (ionic, covalent, and metallic bonding).

Intermolecular forces

Forces that act between stable molecules. Differences in physical properties are the direct result of these forces.

Ionic Bonds

These forces are the strongest of the attractive forces found in compounds.

Most of these compounds are solids (crystalline) at room temperature.

Large amounts of energy are needed to overcome the strong attractive force between positive and negative ions in order to melt it.

Dipole-Dipole

All polar molecules are attracted to each other by these attractions.

Because polar molecules have dipoles, the negatively charged end of the dipole in one molecule is attached to the positively charged end of the dipole in another molecule.

Hydrogen Bonds

Polar molecules containing hydrogen atoms bonded to highly electronegative atoms, specifically fluorine, oxygen, or nitrogen, form especially strong dipole-dipole attractions.

This type of attraction occurs between the partially positive hydrogen atom in one molecule and the partially negative molecule either fluorine, nitrogen, and oxygen.

These bonds are the strongest type of attractive forces between polar covalent molecules.

These bonds are attractions between polar molecules, and no bonds that hold molecules together

Dispersion Forces

These forces are very weak attractions which only occur between nonpolar molecules.

Usually, the electrons in a nonpolar covalent molecule are distributed symmetrically, but the random movement of the electrons may lead to more electrons on one side of the atom than the other, making one side slightly more negative and slightly more positive.

This forms a temporary dipole known as an instantaneous dipole.