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J.J. Thomson: Biography, Facts & Atomic Theory

Instructor: Sara McCubbins

Sara has a background in chemistry education and is currently writing her dissertation in the field of curriculum and instruction.

J.J. Thomson's theories, models, and discoveries relating to electrons and the atomic model of the atom impact our understanding of chemistry today. Below we will explore his life, his discoveries, and his model of the atom.

Thomson and His Discoveries

Many people choose to pursue a career in science, but few impact their field in the way that one English physicist did in the mid 1800s and early 1900s. This physicist, through his experiments, discovered what would come to be known as the electron. He also contributed to the field of chemistry by using this discovery to advance the model of the atom. For these discoveries, he received the Nobel prize in physics, and seven of his former students and assistants also went on to receive Nobel prizes. His name was J.J. Thomson, and this is the story of his life and his discoveries.

J.J. Thomson Biography

Thomson was born on December 18, 1856. His mother was a textile worker, and his father ran an antique bookstore in England. From an early age, Thomson's interest in science was obvious, and he was admitted to Owens College in 1870 at the young age of 14. From there, he went on to Trinity College, Cambridge where he received his BA in mathematics in 1880 and his MA in 1883. He spent the rest of his academic career at Cambridge.

At the young age of 27, Thomson became director of the distinguished Cavendish Laboratory, where he made many discoveries and was an excellent teacher. He married Rose Elizabeth Paget in 1890 and had two children. In 1906, Thomson received the Nobel prize in physics for his discovery of the electron. Two years later, Thomson was knighted. He remained at Trinity College, Cambridge, until his death, and was buried in Westminster Abbey near Sir Isaac Newton.

J.J. Thomson, winner of the 1906 Nobel prize in physics.
J.J. Thomson

Perhaps his greatest contribution, in addition to his discoveries, was his role as a gifted teacher. One of his students, Ernest Rutherford, would go on to disprove Thomson's own model of the atom and eventually take over his post at Trinity College. In total, seven of Thomson's students as well as his own son, all received Nobel prizes for their work.

Discovering the Electron

In the mid-1800s, scientists were studying electrical discharge through evacuated tubes, or tubes that were pumped almost empty of air. These sealed glass tubes, known as cathode-ray tubes, contained a gas inside. When electricity was applied, the tube would glow and emit a ray. Different gases would glow different colors because these rays caused the gases to fluoresce, or give off light.

J.J. Thomson experiment with cathode rays. Cathode rays (blue) emitted by the cathode on the left were deflected by an electric field (yellow) in the center.
Cathode Ray Tube

J.J. Thomson used his experiments to learn more about the properties of these rays, including how different cathodes did not seem to change those properties. He observed that when a metal plate was exposed to the cathode rays, some negative electrical charges built up on the plate and deflected the ray. Not knowing yet what these charges were, he published a paper in 1897 describing his observations, and he concluded that these rays were actually streams of negatively charged particles that had mass. This paper is generally accepted as the discovery of what would later become known as the electron.

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