Intramolecular Forces

Forces present within molecules between the atoms

Comparatively strong forcesChemical properties of substance are related to

its intramolecular forces

Examples

Covalent bond Ionic bondCoordinate covalent bond

Intermolecular Forces

Intermolecular Forces

Set of attractive and repulsive forcesPresent between two moleculesWeak forcesPlay important role in determining the physical

properties of a substanceStates of substance is determined by these forces

Two or more atoms joined by chemical bonds form a molecule

Electrons travel up to the new molecule Electrons are concentrated in the most

electronegativity atom area

Physical Properties of Intermolecular forces

The stronger the intermolecular forces are, the more energy it will require to pull the molecules apart

Molecules that have strong intermolecular forces also have high melting points and boiling points

Examples

Dipole-dipole forcesDipole-induced dipole forcesLondon dispersion forcesHydrogen bonding

Dipole-dipole forces

The attractive forces present between oppositely charged ends of polar molecules are known as dipole-dipole forces

Factors affecting dipole-dipole forces

(i) Electronegativity differenceGreater the electronegativity difference,

greater will be dipole-dipole forces

(ii) Intermolecular distance

Forces are strong in liquids due to less distance between molecules

Forces are weak in gaseous phase due to greater distance between molecules

Dipole-induced dipole forces

The attractive forces present between permanent dipole and induced dipole are called dipole-induced dipole forces

A dipole-induced dipole attraction is a weak attraction

London dispersion forcesThe attractive forces between temporary

dipole in one molecule and temporary induced dipole in an adjacent molecule

The weakest intermolecular force. Present between any two molecules (even

polar molecules) when they are almost touching.

Hydrogen bondingThe force of attraction between

hydrogen atom and electronegative atom of another molecule

Strongest type of intermolecular forces Occurs in molecules with very polar bonds involving

hydrogen

H-F

H-N

H-O Strength of hydrogen bond is twenty times less than that of

covalent bond

The electronegative atoms responsible for creating hydrogen bonding are

Fluorine

Oxygen

Nitrogen

Chlorine

Essential Requirements For An H-bond Are:-

1. A hydrogen atom attached to a highly electronegative atom;

2. Unshared pair of electrons on the electronegative atom.

The

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