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Introduction of Atoms and Molecules


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Introduction of Atoms and Molecules

Around 500BC. An Indian philosopher Maharishi Kanad, postulated that if he go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a time will come when we shall come across the smallest particles beyond which further division will not be possible which is known as “Parmanu”.

  • Ancient Greek philosophers-Democritus and Leucippus called these indivisible particles Atoms.
  • Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.

Laws of chemical combination

This law established after much experimentations by Lavoisier and Joseph L. Proust.

law of conservation of mass: law of conservation of mass states that mass can neither ne created nor be destroyed in a chemical reaction.

Ex-A (reactant) + B(reactant)=AB ( Product)

mass of A + mass of B=mass of AB

Law of constant proportion: In a chemical reaction, compounds always contain the same elements present in definite proportion by mass irrespective of their source.

Ex->

1.)18gm of H2O=2gm of Hydrogen+1gm of Oxygen

mass of hydrogenmass of oxygen=216=18

2.)36gm of H2O=4gm of Hydrogen+32gm of Oxygen

mass of hydrogenmass of oxygen=432=18

This verifies law of constant proportions as the ratio of mass of hydrogen to oxygen is always same.


Types Of Pure Substances

Dalton’s Atomic theory





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