Thomson's Atomic Model

Before 1897, atoms were thought to be indivisible. However, this belief changed when J.J. Thomson discovered the electron, the first subatomic particle.

Thomson’s discovery began with an experiment on cathode rays, which are the streams of particles seen in a cathode ray tube.

This glass tube, with metal electrodes at each end and no air inside, produced a glowing beam when an electric current was passed through the electrodes.

To identify the beam, Thomson placed positively and negatively charged plates near the tube. He observed the beam bent toward the positive plate, showing that it contained some particles that were negatively charged, which he called "corpuscles" and later renamed electrons.

This discovery showed atoms aren’t indivisible; they contain smaller particles like electrons. Since atoms are neutral, Thomson suggested there must be equal positive charges inside.

He proposed the plum pudding model, imagining the atom as a sphere of positive charge, like pudding, with electrons scattered like raisins in it.

This model was later refined by Rutherford and other scientists for a better understanding of the atom's structure.