History of the Atomic Theory Timeline

Democritus

460

Democritus claimed that everything is made up of atoms, as he also said atoms could be physically divided but no geometrically. Democritus claimed atoms were constantly moving and there are an infinite number of them which are indestructible and always will be.

Isaac Newton

Jan 1, 1704

Proposed a mechanical universe with small masses in motion which was had given him the title of having a better perspective on atoms.

John Dalton

Apr 3, 1803

Developed the first useful atomic theory of matter, with spherical solid atoms based upon measureable properties of mass.

Michael Faraday

Sep 7, 1831

Claimed the term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis.

J. Plucker

Oct 19, 1859

Created one of the first gas discharge tubes.

Dmitri Mendeleev

Apr 25, 1869

Dmitri discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.

G.J. Stoney

Oct 19, 1879

Proposed that electricity was made of discrete negative particles he called "electrons".

James Chadwick

Oct 20, 1891

James Chadwick was the discoverer of the neutron. His experiment was to bombard a thin sheet of beryllium with alpha particles. After the experiment he found that the gamma rays emitted from the beryllium contained a third subatomic particle, the neutron.

William Conrad Roentgen

Feb 15, 1895

Discovered x-rays while using cathode-ray tubes. Found that x-rays could pass through solid objects.

George Johnston Stoney

Sep 30, 1897

George Stoney’s most famous work was his conception and calculation of the magnitude of the atom or particle or electricity.

J.J. Thomson

Dec 18, 1897

Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108 coulombs/gram.

Joseph John Thomson

May 30, 1912

In 1912 Joseph Thomson channelled a stream of ionized neon though a magnetic and electric field.In this this he discovered that neon was made of two different types of atoms, this proved the existence of isotopes.

Niels Bohr

Oct 20, 1913

Niels Bohr stated that electrons in an atom do not behave the same as the planets do around the sun. They move about the nucleus in a circular orbit at different distances, the more the energy the further the orbit is from the nucleus.

Ernest Rutherford

Oct 13, 1921

Studied radiations emitted from uranium and thorium and named them alpha and beta. Rutherford established that the nucleus was: very dense,very small and positively charged aswell as he also thought that the electrons were located outside the nucleus.

Aristotle

Mar 2, 2022

Aristotle stated that all matter is made up of the four elements: fire, water, earth and air. His statement was quite generalized and did not come from evidence rather from theories and religious beliefs. There were also four qualities for the elements: dryness, hotness, coldness, and moistness.