Atomic Theory



460 BC - 370 BC

An ancient Greek philosopher who adopted atomic theory from his mentor Leucippus who originally proposed it.


384 BCE - 322 BCE

Aristotle contributed to modern atomic theory by introducing alchemy, an ideology that chemists eventually rebelled against.

Antoine Lavoisier

1743 - 1794

He discovered the Law of Conservation of Mass which states that matter is neither created nor destroyed in a chemical reaction. Atoms are rearranged.

Joseph Proust

1754 - 1826

He discovered the Law of Definite Proportions.

john dalton

09/06/1766 - 07/27/1844

John Dalton reintroduced atomic theory to explain chemical reactions. He also combined the work of Democritus’s definition of atoms and elements, Proust’s Law of Definite Proportions, and Lavoisier’s Law of Conservation of Mass.

William Crookes

1832 - 1919

British chemist and physicist known for his discovery of the element thallium, and his cathode-ray studies, crucial in the development of atomic physics.

Max Planck

April 23, 1858 - October 4, 1947

He found that the energies radiated by hot objects have distinct values, with all other values forbidden. This discovery was the beginning of quantum theory.

Pierre Currie

1859 - 1906

He discovered radium and polonium while studying radioactivity with his wife, Marie Currie.

Marie Curie

1867 - 1934

She is known for the discovery of the elements polonium and radium alongside her husband, Pierre Currie.

Robert Millikan

1868 - 1953

He discovered the charge-to-mass ratio of the electron.

Ernest Rutherford

1871 - 1937

He is the father of nuclear chemistry and physics. He discovered and named the atomic nucleus, the proton, the alpha particle, and the beta particle.

Lise Meitner

1878 - 1968

She along with fellow chemists, Hahn and Strassmann, collaborated with one another to discover uranium fission. She is an important figure in the fields of radioactivity and nuclear physics. She is also widely credited as the discoverer of protactinium.

Albert Einstein

1879 - 1955

Known for the theory of relativity which laid the basis for the release of atomic energy

Otto Hahn (German)

March 8 1879 - July 28 1968

He collaborated with both Lise Meitner and Fritz Strassmann. With Metner, he discovered protactinium, the long-lived mother substance of the actinium series. He also discovered uranium Z, the first case of a nuclear isomerism of radioactive kinds of atoms. He, Meitner and Fritz Strassmann, also collaborated on the processes if irradiating uranium and thorium with neutrons.

Louis Debroglie

1892 - 1987

known for research on quantum theory and predicting the wave nature of electrons

Henri Becquerel


He discovered radioactivity.

Irene Joliot Curie

1897 - 1956

A french scientist who collaborated with her husband, Frederic Joliot-Curie, in researching the structure of an atom. She discovered how to synthesize designer radioactive elements.

Frederic Joliot Curie

1897 - 1956

A french scientist who collaborated with his wife, Irene Joliot Curie, with research on the structure of an atom.

J.J. Thomson

1897 - 1898

He used the Cathode ray tube to describe negative particles called electrons and measured the charge to mass ratio.

Enrico Fermi

1901 - 1954

-An italian physicist who created the world's first nuclear reactor
-Called the "architect of the nuclear age" and the "architect of the atomic bomb

Werner Heisenberg

1901 - 1976

He contributed to the atomic theory by including quantum mechanics, the branch of mechanics, based on quantum theory, used for interpretating the behavior of elementary particles and atoms.

Ernest Lawrence

1901 - 1958

Lawrence invented the cyclotron which is used to discover a large number of new chemical elements and new isotopes.

Robert J. Oppenheimer

1904 - 1967

He was responsible for leading, collecting, and coordinating the team that developed and donated the first atomic bomb.

Niels Bohr


Proposed a theory for the hydrogen atom based on quantum theory. It has three rules:
1.) Electrons only exist in certain allowed orbits
2.) Within an orbit, the electron does not radiate
3.) Radiation is emitted or absorbed when changing orbits

Richard Feynman

1918 - 1988

known for his contributions to the quantum physics

James Chadwick


He found the neutron which has no charge.

Glenn Seaborg

1941 - 1951

He took part in the discovery of ten of the periodic table's chemical elements. Element 106 is named in his honor.