The modern atomic theory is one of the most fundamental theories in chemistry, physics, and other related fields. It explains that matter is made up of atoms which are indivisible and cannot be created or destroyed.

But when was this theory first proposed Let’s take a look back in time.

Early Theories About Atoms

The concept of atoms has been around for thousands of years, dating back to ancient Greek philosophers like Democritus and Leucippus who proposed that everything is made up of small, indivisible particles called “atomos.” However, these ideas were purely theoretical and lacked scientific evidence.

It wasn’t until the 18th century that scientists began to conduct experiments that provided more concrete evidence for the existence of atoms. Joseph Priestley discovered oxygen gas in 1774, and Antoine Lavoisier later showed that oxygen was a component of many substances. John Dalton used this information to propose his atomic theory in 1803.

Dalton’s Atomic Theory

Dalton’s atomic theory consisted of four main points:

While Dalton’s theory was groundbreaking at the time, it had some limitations. For example, it couldn’t explain why elements sometimes combined in more than one ratio to form different compounds.

The Modern Atomic Theory

It wasn’t until the early 20th century that scientists began to develop a more complete understanding of atoms. In 1913, Danish physicist Niels Bohr proposed a new model for the atom based on his observations of atomic spectra.

Bohr’s model consisted of a nucleus made up of protons and neutrons, with electrons in orbit around the nucleus. He also proposed that electrons could only exist in certain energy levels, and that they could jump between levels by absorbing or emitting energy.

This model was further refined by other scientists like Erwin Schrödinger and Werner Heisenberg, who developed quantum mechanics to explain the behavior of subatomic particles.


In conclusion, the modern atomic theory was first proposed by Niels Bohr in 1913. This theory built upon earlier ideas about atoms and provided a more complete understanding of their structure and behavior. Today, the modern atomic theory is a cornerstone of chemistry and other related fields.