J. J. Thomson Joseph John Thomson December 18, 1856 – August 30, 1940 English physicist Served as the President of the Royal

Society in England from 1915 – 1920 He served as the adviser or teacher of

other scientists such as Ernest Rutherford, Niels Bohr, J. Robert Oppenheimer, etc.

J. J. Thomson Published “Treatise on the motion of

vortex rings” that showed Thomson’s interest on atomic theory

Discovery of the electron Discovery of the isotopes of

elements Discovered the natural radioactivity

of potassium

Cathode Ray Tube

Plum-Pudding Model

Plum-Pudding Model The atomic model proposed by J. J.

Thomson in 1904 Atoms were known to consist of

negatively charged electrons Atoms were neutrally charged The negative electrons occupied a

region of space that itself was a uniform positive charge (often considered as a kind of "soup" or "cloud" of positive charge).

Plum-Pudding Model Thomson proposed that the shape of an

atom resembles that of a sphere having a radius of the order of 10-10 m. 

The plum pudding atomic theory assumed that the mass of an atom is uniformly distributed all over the atom.

The plum pudding atomic model was insufficient to explain the structure of an atom.