Ariel Johnson Timeline

Events

Democritus

460 BC

First proposed the existence of an ultimate particle. It was nicknamed "atomos".

Aristotle

384 BC

Believed all substances were made of fire, water, air, and earth. He also believed that if you cut matter in half, you would always have a smaller piece.

Antoine Lavoisier

1743 - 1794

Discovered the Law of Conservation of Matter. Matter is neither created nor destroyed in a chemical reaction.

Joseph Proust

1799

Proposed the Law of Constant Composition.

John Dalton

1803

Discovered the Law of Multiple Proportions and reintroduced the atomic theory to explain chemical reactions.

William Crookes

1870

Discovered Thallium and Cathode Rays

Lise Meitner

1878 - 1968

provided the first theoretical explanation for the splitting of the atom, and coined a new term in physics: fission.

Otto Hahn (German)

March 8 1879 - July 28 1968

Discovered Mesothorium, Protactinium, and Uranium

james Chadwick

1891 - 1932

Discovered this subatomic particle by using a neutron chamber in his experiments.

Henri Becquerel

1896

Discovered radioactivity while experimenting with uranium and a photographic plate.

JJ Thomson

1897

Discovered negatively charged electron. Measured electrons charge-to-mass ratio and identified electrons as fundamental particles.

Marie & Pierre Curie

1898

Discovered Polonium

Max Planck

1900

Proposed the quantum theory. E = H x frequency

Albert Einstein

1905

He proposed that light was made up of quantized photons.

Robert Millikan

1906

Discovered charge on electron. Studied charged oil droplets in an electric field.

Ernest Rutherford

1907

Developed the Gold Foil Experiment

Niels Bohr

1913

Proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined qualities.

Richard Feynman

1918 - 1988

Formulated quantum mechanics

Louis deBroglie

1924

Postulated matter waves. Matter waves in atoms are standing waves.

Werner Heisenberg

1925

Included quantum mechanics to the atomic theory

Robert Oppenheimer

1926

he published many important contributions to the then newly developed quantum theory, most notably a famous paper on the so-called Born-Oppenheimer approximation, which separates nuclear motion from electronic motion in the mathematical treatment of molecules.

Ernest O. Lawrence

1929

invented the cyclotron, a device for accelerating nuclear particles to very high velocities without the use of high voltages.

Enrico Fermi

1934

Evolved the beta-decay theory.

Frederic and Irene Juliot - Curie

1935

Discovered how to synthesize designer radioactive elements

Glenn Seaborg

1940

Discovered Plutonium and all further transuranium elements through element 102