Dalton’s Atomic Theory - Know in detail here

Dalton’s atomic theory was the first theory of atoms and their properties. You will learn about the postulates and limitations of the theory here.
Dalton's Atomic Theory
Dalton's Atomic Theory

Dalton’s Atomic Theory: British physicist, chemist, and meteorologist John Dalton proposed Dalton’s atomic theory in the year 1808. This was the first theory that studied the matter in the form of atoms.

Dalton’s atomic theory suggests that atoms are the smallest particles that cannot be divided further. As per this theory, atoms are indivisible and indestructible.

This theory was based on four postulates. We will discuss the four postulates in detail below.


Postulates of Dalton’s Atomic Theory

  • All the matter in the world is made up of tiny indivisible particles, which are known as atoms.
  • The atoms of a specific element will be identical in mass, size, and other properties, and the atoms of different elements will vary in terms of mass and size.
  • Atoms are neither created nor destroyed which suggests that no atoms are created or destroyed during a chemical reaction.
  • The atoms of different elements can combine with each other in fixed rations to form a compound
  • Atoms can transform into new products by the rearrangement of the existing atoms.


Basis of Dalton’s Theory

Dalton’s atomic theory is based on two principles, which are the law of conservation of mass and the law of constant composition.


Let us learn what these two principles are all about.


Law of Conservation of Mass

The law of conservation of mass states that energy is not created nor transferred in a closed system, which means that during a chemical reaction, each element must be the same in the starting material and product.


Law of Constant Composition

This law states that in a pure compound, the proportion of the elements will be the same for each element.


This theory, although the first such theory in chemistry, had its share of drawbacks, and they were.


Drawbacks of Dalton’s Atomic Theory

The following are some of the drawbacks of the theory proposed by Dalton


  1. It does not consider subatomic particles such as neutrons, protons, electrons etc and the discovery of subatomic particles nullified this theory.
  2. It did not account for the isotopes which are atoms of the same element with different masses.
  3. It does not account for isobars which are elements that have the same mass but different atomic numbers.
  4. It also does not account for the allotropes which are two different compounds made from one element. Like graphite and diamond.
  5. Complex organic compounds do not adhere to the idea of fixed ratio.


When was Dalton's Atomic Theory postulated?

Dalton's Atomic Theory was postulated in 1808.
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