Mike & Matts Atomic Theory Time-Line Project

Aristotle

322

Challenged ideas of Democritus, said there were 4 elements, air, earth, water, and fire. "No matter how many times you cut a form of matter in half, you would always have a smaller piece of that matter."

Domocritus

370

A philosopher, so his ideas were not based on experiments, he believed that atoms were tiny particles that were indestructuble and invisisble.

Joseph Louis Proust

Jan 1, 1724

Discovered "Law of Definite Proportions". In different samples of a chemical compund, proportions of each element in compound is always the same.

Antoine Lavoisier

Jan 1, 1743

Designed a balance that could measure mass.

John Dalton

Jan 1, 1803

First to say that the indivisible unit of an element is the atom and he found that all elemets are composed of tiny indivisible particles, that atoms of the same element are identical, that elements can combine to form compounds, and that chemical reactions occur when atoms are separated or joined or rearranged. Also used experimental methods.

Michael Faraday

Jan 1, 1832

Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism.

Henri Becquerel

Jan 1, 1896

While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.

JJ Thompson

Jan 1, 1897

Discovered electrons and that electrons are in an area within the atom of uniform positive charge.

Marie & Pierre Curie

Jan 1, 1898

Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

Max Planck

Jan 1, 1900

Used the idea of quanta (discrete units of energy) to explain hot glowing matter.

Albert Einstein

Jan 1, 1905

Published the famous equation E=mc^2.

Ernest Rutherford

Jan 1, 1911

Discovered that there is a positively charged nucleus in the atom, and that the nucleus has most of the mass of the atom.

Niels Bohr

Jan 1, 1913

Says there are fixed orbits around the nucleus for the electrons to travel.

Robert Milikan

Jan 1, 1916

Did exeriments with electrons and found out that electrons have one unit of negative charge and the mass is 1/1840 mass of hydrogen atom.

Louis Debroglie

Jan 1, 1923

Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.

Ernest Schrodinger

Jan 1, 1926

Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom. In the current model of the atom, electrons are in regions of space around the nucleus determinded by their energy.

James Chadwick

Jan 1, 1932

Discovered the neutron has no charge and the mass is almost equal to a proton.

Otto Hahn

Jan 1, 1938

Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

Lise Meitner

Jan 1, 1938

Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

Glenn T. Seaborg

Jan 1, 1941

Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.