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400 BCE
Democritus
However, Democritus greatest contribution to modern science was arguably the atomic theory he elucidated. According to Democritus' atomic theory, the universe and all matter obey the following principles: Everything is composed of “atoms”, which are physically, but not geometrically, indivisible. -
322 BCE
Aristotle
Soon after he died, complaining of stomach pains, in 322 BC. 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. -
Antoine Lavoisier
Antoine Lavoisier (1743-1794) 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
He was best known for his discovery of the law of constant composition in 1794, stating that chemical compounds always combine in constant proportions. -
John Dalton
Experiments with gases that first became possible at the turn of the nineteenth century led John Dalton in 1803 to propose a modern theory of the atom based on the following assumptions. ... Matter is made up of atoms that are indivisible and indestructible. 2. All atoms of an element are identical. -
Michael 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
The French scientist Henri Becquerel discovered radioactivity in 1896. ... He realized that some invisible radiation had been emitted from the uranium. He won the Nobel Prize in 1903, along with Marie and Pierre Curie, for his discovery, and the SI unit of radioactivity, the becquerel (Bq), was named after him. -
J.J. Thompson
J.J. Thomson discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He developed the Plum Pudding Model before the atomic nucleus was discovered. -
Marie Currie
For their joint research into radioactivity, Marie and Pierre Curie were awarded the 1903 Nobel Prize in Physics. As a team, the Curies would go on to even greater scientific discoveries. In 1898, they announced the discovery of two new elements, radium and polonium. -
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. Einstein calculates how the movement of molecules in a liquid can cause the Brownian motion. -
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. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. -
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. -
Niels Bohr
Niels Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. -
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. -
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. They have neither a positive nor negative charge, but contribute the the atomic weight with the same effect as a proton.