What Did Dalton’s Atomic Theory State?


Martha Robinson

John Dalton, an English chemist, proposed the Atomic Theory in the early 19th century. This theory was a significant milestone in the field of chemistry as it provided the first scientific explanation of matter. Let’s dive into Dalton’s Atomic Theory and what it stated.

What is Dalton’s Atomic Theory?

Dalton’s theory proposed that atoms are indivisible, indestructible, and fundamental units of matter. Atoms combine to form compounds in fixed ratios. The theory also suggested that chemical reactions occur when atoms are separated, combined, or rearranged; however, they do not change into other elements.

The Postulates of Dalton’s Atomic Theory

Dalton’s atomic theory had five postulates:

Postulate 1: Elements are made up of tiny particles called atoms

Atoms are the smallest particles of matter that retain the chemical properties of an element. For example, all carbon atoms have similar properties.

Postulate 2: Atoms of the same element are identical

All atoms belonging to a particular element have identical properties such as mass and chemical behavior.

Postulate 3: Atoms cannot be divided or destroyed

Atoms cannot be created or destroyed during a chemical reaction; they only rearrange their positions.

Postulate 4: Atoms combine in fixed ratios to form compounds

Chemical compounds consist of two or more different types of atoms combined together in fixed ratios by weight.

  • Law of Multiple Proportions:
  • Compounds containing the same two elements will have different ratios if the elements combine in different ways.

  • Law of Definite Proportions:
  • A pure compound always has the same proportion by mass for each element it contains.

Postulate 5: Chemical reactions occur when atoms are separated, combined, or rearranged

The chemical reaction involves the separation, combination, or rearrangement of atoms. However, atoms do not change into other elements.

Limitations of Dalton’s Atomic Theory

Dalton’s theory was groundbreaking and provided a foundation for modern atomic theory; however, it had some limitations.

  • The existence of subatomic particles:
  • Dalton’s theory did not account for the presence of subatomic particles such as electrons, protons, and neutrons.

  • Isotopes:
  • Dalton’s theory did not explain the existence of isotopes- atoms of the same element with different numbers of neutrons.

  • Molecules:
  • Dalton’s theory did not explain how atoms combine to form molecules.


In summary, Dalton’s Atomic Theory established that everything in our universe is composed of tiny particles called atoms. These fundamental units combine to form compounds in fixed ratios and chemical reactions involve their rearrangement but do not lead to their destruction or creation. While there were some limitations to his theory that later scientists addressed, it provided the foundation for modern atomic theory and helped us understand matter at an atomic level.