The History of the Atomic Theory- Catherine Schilling & Leandra Nikont P.7

Printing Press Invented

Oct 3, 1450

Christopher Columbus discovered America

Oct 23, 1492

Copernicus Claims the Earth Circles the Sun

Oct 3, 1543

America gained Independence from Britain

Jul 4, 1776

Cotton Gin Invented

Oct 3, 1793

Joseph Louis Proust

Feb 27, 1799

In 1799, Proust published his findings and law of definite proportions which explained that if compounds are examined in their individual parts, they will continuously have the same proportions of their individual elements by weight. He also proposed the Law of Constant Composition which stated that the composition of a substance will always be the same, based on his previous findings.

John Dalton

Sep 26, 1803

Dalton had his own ideas about atomic theory. 1) Substances are made of atoms which cannot be created, divided, or destroyed. 2) Atoms of the same element are exactly alike. 3) Atoms combine with other atoms to create new substances.

First Photograph

Oct 3, 1839

Eifel Tower built

Oct 3, 1890

J.J. Thomson

Sep 24, 1897

Discovered negatively charged electrons which he called corpuscles. He disproved the part of Dalton's theory saying that atoms cannot be divided. He also recognized that there needed to be a positively charged part to balance the negative. Formed the Plum pudding model.

Ernest Rutherford

Oct 29, 1898

Rutherford introduced the existence of alpha and beta rays in uranium radiation. He also analyzed some of their properties. He and H. Geiger produced a method to detect an alpha particle and counting the number emitted from radium. Also, he and R.B. Owens discovered the isotope of radon, which is now known as thoron (a noble gas).

Henri Becquerel (1899-1900)

Dec 16, 1899

Becquerel, overall, made three contributions to the atomic theory. The first was that he measured the deflection of beta particles (a component of the radiation in magnetic/electric fields). He showed that the beta particle was also the same as Thomson’s, recently, discovered and not yet identified electron. Lastly he noticed that active substances in uranium would lose its radiation throughout time, but would regain its radioactivity over time again.

Max Planck

Oct 2, 1901

Planck discovered what he called quanta, non-continuous energy delivered in small pieces.

Robert Millikan

Sep 19, 1909

Millikan realized the single unit charge of any electron from an oil drop experiment at the University of Chicago, this allowed for calculation of mass of an electron and positively charged atoms. His equation was:
e = 1.60 x 10-19 coulombs

Niels Bohr

Sep 26, 1913

Bohrs suggested that electrons move in definite paths in energy levels. The also suggested that they could switch paths.

World War I Began

Jul 28, 1914

Louis de Brogllie

Dec 9, 1921

Brogllie introduced the idea that particles could sometimes behave as waves. With this is mind, waves could also behave as particles. He also introduced an equation to represent his findings:
=h/p
h=Planck's constant = 6.634x10-34 Js
p=(mass)x(velocity)

Erwin Schrödinger

Oct 2, 1926

Schrodinger created the basis for Bohr's model. It was called Schrodinger's wave equation used to find the probable location of an electron.

Werner Heisenberg

Jul 8, 1927

Although many rejected his ideas, Heisenberg ealized that if an electron was hit by gamma rays, to measure its properties, it would ultimately change the electron’s behavior. This idea became a fundamental law of nature.

James Chadwick

Oct 2, 1932

Chadwick, with the help of Ernest Rutherford, discovered that there are neutraly charged particles in the neutron. He determined that neutrons, as he called them, had .1% more mass than the proton and that this accounted for the atomic mass being so large. However, he believed that the neutron was an electron and a proton paired together. None the less he won a noble prize for his discovery 1935.

World War II Began

Sep 3, 1939

First use of Paper

Jun 18, 2004

Paper replaced stone, slate, papyrus and vellum.