Final answer:
J.J. Thomson was a physicist known for his discovery of the electron and his plum pudding model of the atom. His work falls in the late 19th and early 20th centuries.
Step-by-step explanation:
J.J. Thomson was a physicist who is known for his discovery of the electron and his development of the plum pudding model of the atom. Thomson's experiments with cathode rays led to the discovery that cathode rays were streams of particles, called electrons, that are present in the atoms of all elements. His plum pudding model, proposed in 1904, described the atom as a uniform sphere of positive charge with embedded electrons.
In terms of the timeline of history, J.J. Thomson's work falls in the late 19th and early 20th centuries. He made his discovery of the electron in 1897 and proposed the plum pudding model in 1904. However, his model was later replaced by Ernest Rutherford's nuclear model of the atom around five years later.