The man who proved atoms are not the smallest building blocks
In 1897, the scientific world believed atoms were the fundamental, indivisible units of matter. J.J. Thomson changed everything by demonstrating that a much smaller, negatively charged particle exists within them, effectively shattering the idea of the atom as an unbreakable sphere.
At the end of the 19th century, physicists were divided over the nature of cathode rays. Many German scientists believed these rays were immaterial waves traveling through a weightless substance called 'the ether.' However, Thomson, using an improved vacuum technique in his Crookes tubes, sought to prove they were actually particles of matter.
By applying both electric and magnetic fields to these rays, Thomson observed that their deflection was consistent regardless of the gas used in the tube. He calculated a mass-to-charge ratio over 1,000 times smaller than that of a hydrogen ion. This led him to conclude that these 'corpuscles'—now known as electrons—were universal, subatomic building blocks present in all atoms.
This discovery led to Thomson's famous 'plum pudding model' in 1904, which envisioned the atom as a sphere of positive matter containing embedded, rapidly orbiting electrons. While this model was later refined, his work laid the foundation for modern atomic physics. His influence extended far beyond his own laboratory; Thomson was a prolific mentor, with seven of his students, including Ernest Rutherford, going on to win Nobel Prizes.
Thomson's legacy is also found in the development of mass spectrometry. In 1912, alongside Francis William Aston, he used canal rays to provide the first evidence of isotopes in stable elements, such as neon-20 and neon-22, by measuring the deflection of ions through electric and magnetic fields.
Source: J. J. Thomson
