-
500
Democritus
First person to suggest that matter can not be infinitely divided. He described atoms as tiny particles that make up matter and move through empty spaces. -
505
Aristotle
He disagreed with Democritus' idea that atoms move through empty space and he completely denied the existence of atoms due to his personal ideas about nature. He also developed the scientific method. -
John Dalton
He marked the beginning of modern atomic theory. He described atoms as small particles of matter that are indivisible and indestructible. He stated that the chemical reaction is a rearrangement of atoms. -
J. J. Thompson
He designed a series of experiments at Cambridge to determine the ratio of a particle's charge to its mass. He went against Dalton's theory that atoms were indivisible. He proved that the atom was divisible. -
Ernest Rutherford
He studied how positively charged particle interacted with solid matter. He designed an experiment to see if the particles would be deflected as they pass through a thin piece of gold foil. In a later experiment, he realized that protons were inside of the nucleus. -
Robert Milikan
He designed an oil drop apparatus to figure out the charge of an electron. He also discovered the mass of an electron. The charge carried by the electron also demonstrated the atomic structure of electricity. -
James Chadwick
He demonstrated that the nucleus had another particle, the neutron. He established that the atomic number is determined by the number of protons in an atom.
