What Are the Postulates of Dalton’s Atomic Theory of Matter Class 9?


Vincent White

John Dalton was a renowned English chemist and physicist who is widely known for his contributions to the development of modern atomic theory. His groundbreaking research in the field of chemistry led to the formulation of the Dalton’s Atomic Theory of Matter, which forms the foundation of modern-day chemistry. In this article, we’ll explore the postulates of Dalton’s Atomic Theory of Matter Class 9.

Postulate 1: Matter is made up of tiny indivisible particles called atoms

Dalton proposed that all matter is composed of extremely small indivisible particles called atoms. According to him, atoms are the smallest units of matter that cannot be divided further.

Postulate 2: Atoms of an element are identical in all aspects

Dalton believed that all atoms belonging to a particular element have identical properties such as mass, size, and chemical behavior. This means that each element has its unique atom with specific properties.

Postulate 3: Atoms combine in definite proportions to form compounds

Dalton proposed that chemical compounds are formed when two or more different types of atoms combine in a fixed ratio. This means that the ratio between different types of atoms in a compound is always constant.


  • Water is composed of two hydrogen atoms and one oxygen atom (H2O).
  • Methane (CH4) contains one carbon atom and four hydrogen atoms.

Postulate 4: Chemical reactions occur when atoms are rearranged or combined

Dalton suggested that chemical reactions take place when atoms are rearranged or combined with other atoms to form new compounds. He also stated that during chemical reactions, no new atoms are created or destroyed; they only change their arrangement.

Limitations of Dalton’s Atomic Theory of Matter

While Dalton’s Atomic Theory of Matter was groundbreaking in its time, it had a few limitations that were later addressed by other scientists. For example, he assumed that atoms were indivisible and had no internal structure. However, later research showed that atoms are made up of subatomic particles such as protons, neutrons, and electrons.


In conclusion, Dalton’s Atomic Theory of Matter remains an essential contribution to the field of chemistry. His postulates form the foundation of modern-day chemistry and are still relevant today. While his theory had a few limitations, later research has built upon his work to create a more comprehensive understanding of atoms and their behavior.