Postulates Of Dalton�s Atomic Theory - Science Class 9

 

What is matter? What is the nature of matter? How the nature of matter can explain the Laws of chemical combination? John Dalton put forward a theory in 1808 about the nature of matter. The theory is based on certain postulates called Postulates of Dalton�s Atomic Theory.

The theory is based on the concept of matter, which was put forward by the ancient philosopher like great Indian philosopher Kanad & Greek philosopher Leucippus.

Postulates of Dalton�s Atomic Theory:-
� All the matter is made up of extremely small particles called Atoms.
� Atoms of the same element are identical in all aspects i.e. size, shape, mass, and properties.
� Atoms of different elements have different sizes, shapes, and masses and also possess different properties.
� Atoms of the same or different elements combine together to form molecules or compounds.
� When atoms of different elements combine together to form compounds, they do so in a simple whole-number ratio such as 1:2, 2:1, 2:3, etc.
� Atom of two different elements may combine in different ratios to form more than one compound.
� The number and kind of atoms in a given compound are always fixed.
� Atom is the smallest particle that takes part in a chemical reaction.
� An atom can neither be created nor be destroyed i.e. an atom is indestructible.

In this way, Dalton presented the Postulates of Dalton�s Atomic Theory, which has become a milestone in the study of matter.

 

Law of chemical combination by Dalton's Atomic theory

 

Explanation of Laws of chemical combination by Dalton�s Atomic theory.

 

Laws of Conservation of mass: According to Dalton�s atomic theory, the atom is the smallest particle that takes part in a chemical reaction and the atom can neither be created nor be destroyed. The total number and kind of atoms remain the same in a chemical reaction. Therefore, the total mass remains unchanged during a chemical reaction.

 

Law of constant proportion: According to Dalton�s atomic theory, the number and kind of atoms in a compound are fixed. This implies that a compound is always made up of the same elements. Further, the number of atoms of different elements in the compound is fixed. This means that in a compound, atoms combine in a fixed whole number ratio.

 

Since the atoms have fixed mass, therefore in a compound, the elements are combined in a fixed ratio by mass. Combination of both the results given us the law of constant proportion.

 

Read More: Laws of Chemical Combination: Explanation - Science Class 9