Once upon a time, after Dalton’s Atomic Theory was released to the world, J.J Thompson conducted experiments that led to contradicting Dalton’s theory. Thompson discovered the presence of subatomic atoms called electrons, disproving the theory that all atoms are indivisible. His model of atomic structure was known as the Plum Pudding Model (look carefully – it actually does look kind of like a plum colored pudding).
Scientists always debated the rightness of Dalton’s theory, as how electrical currents were carried still remained a mystery. If atoms made up everything and they were the smallest of the smallest particles, then how did something conduct electricity? The statics when you touch a metal, the lights that light your house – where did they all come from? This mystery was finally resolved with Thompson’s findings with the Cathode-Ray experiment. Cathode-ray, also known by electron beams, are streams of electrons observed in discharge tubes*. Thompson measured the mass of cathode-rays and proved that they were made of particles. However, he found out that they were still heavier than the lightest atom – hydrogen. Therefore, they were not atoms – indeed, they were the first subatomic particles ever discovered. (Fun fact: Thompson named these particles corpuscles, but they were later changed to electrons)
To summarize, Thompson discovered electrons(negatively charged subatomic particles) and proposed the Plum-Pudding Model, disproving Dalton’s Atomic Theory. In the next article, we will discuss about Ernest Rutherford’s Gold Foil Experiment.
*Discharge Tubes: an electron tube which contains gas or vapor at low pressure and through which conduction takes place when a high voltage is applied. (Merriam-Webster)
