J.J. Thomson was the scientist who discovered the electron in 1897. Before his work, atoms were thought to be the smallest, indivisible parts of matter. Thomson used a device called a cathode-ray tube, which sends electric currents through rarefied gases in a glass tube.

Inside the tube, he noticed rays that moved from the negatively charged plate (cathode) to the positive plate (anode). By applying electric and magnetic fields, he measured how these rays bent. From the way they bent, he calculated the mass-to-charge ratio of the particles making up the rays. His measurements showed that these particles were much lighter than any known atom.

Thomson called these particles “corpuscles,” but today we know them as electrons. His discovery proved that atoms are not indivisible: they contain smaller, negatively charged parts. This finding was the first step toward our modern model of the atom, which includes a dense nucleus surrounded by electrons.

Thomson’s work led to a new understanding:
1. **Atoms have internal structure.** They are made of smaller parts.
2. **Electrons carry negative charge.** They play a key role in chemical bonds, electricity, and magnetism.
3. **Physics and chemistry advanced.** Knowing about electrons opened up the study of electronics, from light bulbs to computers.

Later scientists built on Thomson’s discovery. Rutherford found the nucleus, Bohr described electron orbits, and quantum mechanics gave us a deeper picture of how electrons behave.

In simple words, J.J. Thomson looked at how electric rays moved in a vacuum tube. He saw that these rays were made of tiny, negative particles. That was the first time anyone had seen an electron. His work changed science forever and led to everything from radios and x-rays to modern electronics.