Class 11 Physics Kinetic Theory Molecular nature of matter

Molecular nature of matter

John Dalton

  • Atomic hypothesis was given by many scientists. According to which everything in this universe is made up of atoms.
  • Atoms are little particles that move around in a perpetual order attracting each other when they are little distance apart.
  • But if they are forced very close to each other then they rebel.
    • For example: - Consider a block of gold. It consists of molecules which are constantly moving.
  • Dalton’s atomic theory is also referred as the molecular theory of matter.This theory proves that matter is made up of molecules which in turn are made up of atoms.
  • According to Gay Lussac’s law when gases combine chemically to yield another gas,their volumes are in ratios of small integers.
  • Avogadro’s law states that the equal volumes of all gases at equal temperature and pressure have the same number of molecules.
  • Conclusion: - All these laws proved the molecular nature of gases.
  • Dalton’s molecular theory forms the basis of Kinetic theory.

Why was Dalton’s theory a success?

  • Matter is made up of molecules, which in turn are made up of atoms.
  • Atomic structure can be viewed by an electron microscope.

Solids, Liquids, Gases in terms of molecular structure

Basis of Difference




Inter Atomic Distance(distance between molecules).

Molecules are very tightly packed.  Inter atomic distance is minimum.

Molecules are not so tightly packed. Inter atomic distance is more as compared to solids.

Molecules are loosely packed .Free to move. Inter atomic distance is maximum.

Mean Free Path is the average distance a molecule can travel without colliding.

No mean free path.

Less mean free path.

There is mean free path followed by the molecules.


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