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500 BCE
The Alchemists
They laid down the basis for the periodic table of elements, which contributed to the atomic theory. -
450 BCE
Aristotle
He did not believe in the atomic theory, and instead taught that everything is made of small amounts of the four elements; earth, fire, water, and air. -
427 BCE
Plato
Introduced the theory that atoms of different types are all different shapes, and that there wasn't only 5 fundamental elements that make up atoms, and he labeled a sixth called "ether," which made up stars. -
400 BCE
Democritus
He created the theory that everything is made up of atoms, which cannot be seen, and that can't be destroyed and will always be in motion. -
Robert Boyle
He created an indefinite definition of an atom, saying that if it could be broken into two or more substances, it wasn't an atom. He also disproved the four element atom theory. -
Lavoisier
He figured out that oxygen was an element, and that it couldn't be changed because there was no way to break it down. He also named oxygen and proposed that it was key in combustion, along with discovering other elements. -
John Dalton
Created the theory that all matter is composed of atoms, which were invisible and indestructible, and atoms of the same element were identical, but atoms of different elements could be different shapes and/or sizes. He also created the "Billiard Ball" atom model. -
Dmitri Mendeleev
He put all known chemicals in an order of increasing atomic weight, resulting in the periodic table of elements. He also wrote the principles of chemistry. -
Robert Millikan
He discovered the value of an electron charge using an oil drop experiment, and continued research on elemental electronc charge and the photoelectric effect. -
J. J. Thompson
He discovered that all atoms have negatively charged electrons/subatomic particles, and he created the plum pudding model. -
The Curies
They studied radioactivity and won a Nobel prize for the discovery of the elements radium and polonium. -
Albert Einstein
Proved the existence of atoms through statistics and probability, and that all liquid is made of molecules that are always moving in random motion. He also created E=mc^2, which eventually gave birth to the atomic bomb. -
Ernest Rutherford
Created the theory for the nuclear structure of an atom, discovered alpha beta rays, and created the theory of radioactive decay, along with creating the Rutherford atom model. -
Neils Bohr
He created the Solar System model, which proposed how electrons could orbit around the nucleus and remain stable. -
Henry G. J. Moseley
He created the "Moseley Law," which states that the X-Ray frequency of an atom is determined by the atomic number and the atomic weight. -
Werner Heisenburg
He created the uncertainty principle, which states that it isn't possible to exactly guess a particle's position at any given time. He also contributed to quantum mechanics in terms of matrices, along with creating the electron cloud model.
