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400 BCE
Aristotle
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matte -
370 BCE
Democritus
The atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” According to Democritus atoms were miniscule quantities of matter. -
Antoine Lavoisier
Antoine Lavoisier was the first person to make good use of the balance. He was an excellent experimenter. After a visit with Priestly in 1774, he began careful study of the burning process. He proposed the Combustion Theory which was based on sound mass measurements. -
Joseph Louis Proust
Law of Definite Proportions (or Law of Constant Composition) in 1794. This law states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. -
John Dalton
Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Micheal Faraday
Faraday was an English scientist who contributed to the fields of electromagnetism and electrochemistry. His main discoveries include those of electromagnetic induction, diamagnetism and electrolysis -
Henri Becquerel
Henri Becquerel made an important contribution to our understanding of atomic theory when he discovered the existence of radioactivity. -
J.J Thomson
J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas. -
Marie & Pierre Curie
In 1898, they announced the discovery of two new elements, radium and polonium. ... In 1906, Pierre was killed in a traffic accident. -
Albert Einstein
Albert Einstein became famous for the theory of relativity, which laid the basis for the release of atomic energy. In 1905 Albert Einstein formulates Special Theory of Relativity. -
Robert Millikan
His oil drop experiment helped to quantify the charge of an electron, which contributed greatly to our understanding of the structure of the atom and atomic theory. -
Ernest Rutherford
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, heavy nucleus. -
Neils Bohr
In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. -
Max Planck
Max Planck, a German physicist, is best known as the originator of the quantum theory of energy for which he was awarded the Nobel Prize in 1918. His work contributed significantly to the understanding of atomic and subatomic processes. -
James Chadwick
James Chadwick played a vital role in the atomic theory, as he discovered the Neutron in atoms. Neutrons are located in the center of an atom, in the nucleus along with the protons.