Which scientist discovered the electron and proposed the plum pudding model?

• A. J.J Thomson
• B. John Dalton
• C. Empedocles
• D. Democitus

Answer: (A)

The idea being tested is identifying who first discovered the electron and proposed a model of the atom that includes electrons arranged within a positively charged substance. That scientist is J. J. Thomson. He used experiments with cathode rays to measure the charge-to-mass ratio of particles, showing there are components much smaller than atoms and that these particles carry negative charge—the electron. From these findings he proposed the plum pudding model, envisioning the atom as a positively charged ball with negatively charged electrons embedded inside, like raisins in pudding. This helped explain why atoms are overall neutral despite containing charged particles. The model stood for a time but was later refined by Rutherford’s gold foil experiment, which revealed a tiny, dense nucleus at the center of the atom. For context, John Dalton proposed that matter is made of indivisible atoms, but he did not describe electrons or the plum pudding idea, and Empedocles and Democritus had ancient ideas about atoms that predate the discovery of electrons.