Dalton’s Atomic Theory is one of the fundamental concepts in chemistry that laid the foundation for modern atomic theory. It was proposed by John Dalton in the early 19th century and was based on his experiments and observations of various chemical reactions.

The theory consists of several postulates that describe the behavior of atoms and molecules in chemical reactions. However, there is one postulate that is not part of Dalton’s Atomic Theory, and in this article, we will explore which one it is.

The Postulates of Dalton’s Atomic Theory

Before we dive into the missing postulate, let’s first review the postulates that make up Dalton’s Atomic Theory:

1. All matter is made up of tiny, indivisible particles called atoms. 2. Atoms of a given element are identical in size, mass, and chemical properties.

3. Atoms cannot be created or destroyed in a chemical reaction; they can only be rearranged. 4. When atoms combine to form compounds, they do so in simple whole number ratios.

These four postulates formed the basis for understanding atomic structure and chemical reactions at the time they were proposed by Dalton.

The Missing Postulate

So, which postulate is not part of Dalton’s Atomic Theory? It turns out that there isn’t a missing postulate per se – rather, it’s a limitation of the theory itself.

One limitation is that it assumes all atoms of a given element have identical properties. However, we now know that isotopes exist – atoms of an element with different numbers of neutrons – which have slightly different properties.

Another limitation is that it doesn’t account for subatomic particles such as protons, neutrons, and electrons. These particles were discovered after Dalton proposed his atomic theory and are essential to our current understanding of atomic structure.


In conclusion, there isn’t a missing postulate in Dalton’s Atomic Theory, but there are limitations to the theory that have since been addressed by modern atomic theory. Despite its limitations, Dalton’s Atomic Theory was a significant contribution to the field of chemistry and laid the foundation for our current understanding of atomic structure and chemical reactions.