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442 BCE
Democritus 460-370 BC
Democritus did his theory saying that everything was made of small particles that were indivisible. -
John Dalton 1766-1844
With his model he showed the "atomic theory of matter", in which he said that: everything is made of atoms, atoms made of the same element are alike, atoms are impossible to destroy or divide, atoms of different elements can combine to make compounds, and that chemical reactions happen when atoms are combined, separated, or rearranged. -
Eugen Goldstein 1850-1930
He discovered protons with the cathode ray experiment, the rays knocked the electrons of atoms and attracted them to positive charge electrodes. -
J.J. Thomson 1856-1940
His model was the "Plum Pudding Model". He described every atom as a circle full of positive charge fluid. Sparsed in it were electrons. -
Lord Ernest Rutherford 1871-1937
After many experiments with radioactive particles he discovered many things for his model. He said that atoms had a small center called the nucleus, filled with positive charge. Also he said that electrons surrounded the nucleus and were held in orbit. -
Niels Bohr 1885-1962
He expanded Rutherford's ideas. He added that electrons moved in circular orbits around the nucleus called "electron shells". Stated that the farther they were from the nucleus, the more energy thay had. -
James Chadwick 1891-1974
Chadwick said that there was more than just protons and electrons, and he discovered neutrons, but he said that they were hard to find. His experiments started a concept that consisted in saying that the protons and neutrons are made of smaller particles called quarks.