Atomic Model Timeline By Kaitlyn Dunbar

Democritus

325

He discovered the existence of invisible atoms,
characterized only by quantitative properties: size, shape, and motion.

Antoine Lavoisier

Dec 17, 1770

Lavoisier demonstrated that transmutation of water to earth was not possible, but that the sediment observed from boiling water came from the container. He burnt phosphorus and sulfur in air, and proved that the products weighed more than he original. Nevertheless, the weight gained was lost from the air. Thus he established the Law of Conservation of Mass.

John Dalton

Dec 17, 1803

He proposed the Atomic Theory which stated that (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules).
(not actual month and day)

Joseph Proust

Dec 18, 1808

He established the steadiness of the composition of chemical compounds.

William Crookes

Dec 17, 1875

He developed the Crookes tubes, investigating canal rays.
(not right month and day)

Henri Becquerel

Dec 17, 1896

He discovered the phnomen of natural radioactivity. (not actuall month and day of discovery)

Marie Curie

Dec 17, 1896

She and her husband discovered polonium, named after the country of Marie's birth, and radium.
(not the right month and day)

Joseph Thomson

Apr 30, 1897

Thomson discovered that cathode rays were negatively charged particles which he called 'corpuscles.' He also discovered that they had a mass about 1000 times smaller than a hydrogen atom, and he claimed that these corpuscles were the things from which atoms were built up.

Plum Pudding Model

Dec 18, 1897

J.J. Thomas found that an atom as a plum pudding that has negatively charged electrons uniformly arranged inside an atom.

Cathode Ray Tube Experiment

Dec 18, 1897

JJ Thomson discovered electron using a cathode ray tube; changed model to the Plum Pudding Model where negative electrons float in positive "pudding".

Rutherford's Nuclear Atom

Nov 18, 1909

Rutherford thought that all the alpha particles with a charge +2e were brought together into a little %u2018ball%u2019 by Coulomb%u2019s repulsive force, which has the charge +Ze. He called this area the atomic nucleus or nucleus.

Planetary or solar system model

Dec 18, 1909

Ernest Rutherford developed the Planetary Model where the nucleus is in the center and the electrons orbited around the nucleus like planets around the sun

Oil Drop Experiment

Dec 18, 1909

Robert Millikin measured charge and mass of electron doing the Oil Drop Experiment

Gold Foil Experiment

Dec 18, 1909

Ernest Rutherford did the Gold Foil Experiment where he discovered the nucleus- a small, dense, positively charged area in the center of the atom.

Robert Millikan

Dec 17, 1910

The Millikan oil-drop experiment was far superior to previous determinations of the charge of an electron.

Niels Bohr

Dec 17, 1913

He discovered that electrons travel only in certain orbits and that any atom could exist only in a discrete set of stable states.
(not the correct month and day)

Henry Moseley

Dec 18, 1913

Moseley published the results of his measurements of the wavelengths of the X-ray spectral lines of a number of elements which showed that the ordering of the wavelengths of the X-ray emissions of the elements coincided with the ordering of the elements by atomic number.

Electron Cloud Model

Dec 18, 1913

Neil Bohr discovered a small, positively charged nucleus is in the centre, surrounded by electrons in orbit.

James Chadwick

Dec 17, 1932

He proved the existence of neutrons.

Invisible, solid sphere model

Dec 18, 1932

Leucippus and Democritus%u2019s first ever atomic model.