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Period: 460 BCE to 370 BCE
Democritus
His ideas about atoms were rudimentary compared to our concepts today, they outlined the idea that everything is made of atoms, invisible and indivisible spheres of matter of infinite type and number (https://en.wikipedia.org/wiki/Democritus) -
John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
(https://en.wikipedia.org/wiki/John_Dalton) -
Joseph John Thomson
In 1897 he discovered the electron and the fact that it had a negative charge. Thompson knew that there must be a source of positive charge in the atom due to the atom because neutral charge. This lead to him discovering the plum pudding model in 1904. In this model, an atom is thought of as a round ball of positive charge with negatively charged electrons embedded in it. Like plums in a plum pudding, hence the name plum pudding model.
