Atomic Theory and Atomic Model

Democritus (460-370 BC)

460

Democritus was the first philosopher to propose the existance of the atom calling it the atomus.

Alchemists (500 BC- 1720)

500

Discovered that metals can be changed onto other substances making them study the particles of metals which led to the atom.

Benjamin Franklin

Apr 23, 1752

Proposed that matter has positive and negative charges from his stormy kite flight attached with a metal key experiment.

Stormy Kite flight

Apr 23, 1752

Antoine Lavoisier

Apr 23, 1777

Discovered the law of Conservation of Mass.

Joseph Proust

Apr 23, 1799

Developed the Law of Constant Composition which is the law that mass cannot be gained or depleted through a reaction or experiment.

John Dalton

Apr 23, 1803

John Dalton proposed that matter has positive and negative charges.

Michael Faraday

Apr 23, 1832

Michael Faraday developed the Laws of Electrolysis which is splitting molecules with electricity.

Electrolysis Experiment

Apr 23, 1832

Dmitri Mendeleev

Apr 23, 1869

Dmitri Mendeleev discovered the Periodic Law which help build the periodic table and the formula for atoms

William Crookes

Apr 23, 1879

William Crookes discovered cathode rays are deflected by electric fields and magnets suggesting a negative charge.

Cathode Ray Tube

Apr 23, 1879

G.J. Stoney

Apr 23, 1894

G.J. Stoney proposed that electricity was made of discrete negative particles he called electrons.

Henry Becquerel

Apr 23, 1896

Discovered radioactivity.

J.J. Thomson

Apr 23, 1897

J.J. Thomson discovered the charge to mass ration of an electron using the Cathode Ray Tube Experiment. This discovery also helped him create the Plum Pudding Model.

Cathode Ray Tube Experiment

Apr 23, 1897

Plum Pudding Model

Apr 23, 1897

Marie & Pierre Curie

Apr 23, 1898

Marie & Pierre Curie discovered that radiation breakes down particles spontaneously which released subatomic particles and radiation in the form of energy.

Max Planck

Apr 23, 1900

Max Planck used the idea of discrete units of energy to explain hot glowing matter. He called these discrete units of energy quanta.

Hantaro Nagaoka

Apr 23, 1903

Hantaro Nagaoka created the Saturnian Model which has flat rings of electrons revolving around a positively charged particle.

Saturnian Model

Apr 23, 1903

Albert Einstein

Apr 23, 1905

Albert Einstein developed the equation for for energy which is mass times speed of light squared.

Equation of Energy

Apr 23, 1905

Oil Drop Experiment

Apr 23, 1909

Robert Millikan

Apr 23, 1909

Robet Millikan determined the charge and mass of an electron through the Oil Drop Experiment.

Ernest Rutherford

Apr 23, 1911

Ernest Rutherford found that the positive charge and mass of the atom occupied a small volume in the center and the rest was empty space through the Gold Foil Experiment.

Gold Foil Experiment

Apr 23, 1911

Henry Moseley

Apr 23, 1914

Henry Moseley discovered the atomic number which is the number of protons in an element.

Francis Aston

Apr 23, 1920

Francis Aston discovered isotopes.

Niels Bohr

Apr 23, 1922

Created the Bohr Model

Bohr Model

Apr 23, 1922

Louis de Broglie

Apr 23, 1923

Louis de Broglie discovered that electrons had a duel nature similar to particles and waves.

Werner Heisenberg

Apr 23, 1927

Discovered the Principle of Indeterminancy.

Electron Cloud

Apr 23, 1930

Erwin Schrodinger

Apr 23, 1930

Erwin Schrodinger discovered the electron cloud.

James Chadwick

Apr 23, 1932

Discovered neutrons in the nucleus giving the world the third atomic particle.

Neutron

Apr 23, 1932

Aristotle (384-322 BC)

Mar 2, 2022

Aristotle proposed that all matter consisted of four elements: earth, air, water, and fire. He also proposed that all matter consisted of four qualities: dryness, hotness, coldness, and wetness.

Aristotle diagram

Mar 2, 2022

Atomic theory and Atomic Model Timeline

Period: Mar 2, 2022 to Apr 23, 1932