How Did JJ Thomson Discover His Atomic Theory?


Vincent White

In the late 1800s, the world of science was buzzing with excitement as new discoveries and breakthroughs were being made. One such discovery was that of the atom, and it was JJ Thomson who made a major contribution to our understanding of this fundamental building block of matter.

JJ Thomson: A brief history

Joseph John Thomson, also known as JJ Thomson, was born in 1856 in Manchester, England. He went on to study at Trinity College, Cambridge and eventually became a professor at the same institution. Throughout his career, he made significant contributions to the field of physics and is credited with discovering the electron.

The discovery of the electron

In the late 1800s, scientists were trying to understand what atoms were made of and how they behaved. It was believed that atoms were indivisible, but JJ Thomson’s work showed otherwise. In 1897, he discovered electrons by experimenting with cathode ray tubes.

Thomson reasoned that if he could determine how these rays were affected by electric and magnetic fields, he could learn more about their nature. He found that cathode rays were deflected by both electric and magnetic fields in a way that suggested they were negatively charged particles.

This led him to propose his famous “plum pudding” model of the atom – an atom composed of negatively charged electrons embedded in a positively charged sphere.

The atomic theory

Thomson’s discovery of the electron paved the way for further research into atomic structure. His work on cathode rays provided evidence for the existence of subatomic particles and helped scientists understand how atoms behave.

Thomson’s atomic theory proposed that atoms are made up of positively charged material with negatively charged electrons dispersed throughout it. This marked a significant departure from previous theories which suggested atoms were indivisible.


JJ Thomson’s discovery of the electron and subsequent work on atomic structure revolutionized the field of physics. His contributions laid the foundation for further research and experimentation, which eventually led to a more complete understanding of atoms and their behavior.

Today, we still use many of the concepts that Thomson introduced in our understanding of the subatomic world. His work serves as a reminder that even small discoveries can have a big impact on our understanding of the world around us.