Molecular Theory of Matter

Key Points  

- All matter is made up of tiny particles called molecules.  

- Molecules of a substance are alike in size, shape, composition, and properties.  

- Molecules differ between different substances.  

- Molecules are in continuous and random motion, which gives them kinetic energy.  

- Molecules have spaces between them, known as intermolecular space.  

- Molecules are attracted to each other by a force called the intermolecular force of attraction.  

Intermolecular Force of Attraction Depends On  

a) Intermolecular Space  

- The greater the intermolecular space → weaker the force of attraction.  

b) Nature of the Molecule  

- Molecules of the same kind exert a force of cohesion.  

  - This binds molecules together.  

  - Cohesion is maximum in solids, lesser in liquids, and least in gases.  

- Molecules of different kinds exert a force of adhesion.  

- Kinetic energy of molecules increases with temperature.