History of Atomic Theory

Democritus (400 BCE)

Jan 1, 1001

Said that atoms were small and hard, are made of a single material, are always moving, and join together.

Aristotle (350 BC)

Jan 1, 1001

Believed in 5 elements, earth, wind, water, fire, and ether, and believed that they made up everything.
Images: http://no-pedia.com/aristotle.html, http://image.shutterstock.com/display_pic_with_logo/381733/381733,1326132509,3/stock-vector-the-four-elements-of-nature-air-earth-fire-water-92339143.jpg

John Dalton

Jan 1, 1808

Said that atoms make up everything and cannot be created, destroyed, or split, and that the same types of atoms are identical, and other types are different. Also said that atoms form different substances, and chemical reactions rearrange atoms in compounds
[https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcTZWVqEKiANj5n9TVuvOPmu2vEwJc3qdLg6WI6CIAqW5Hy0cUyK]
Image: https://commons.wikimedia.org/wiki/File:Coypel_Democritus.jpg, http://www.google.com/url?sa=i&source=images&cd=&docid=h-7AqvvbG

Sir William Crookes

Jan 1, 1855

Used a glass tube with electrodes to see the path of electricity, and discovered that electrons have mass, negative charge, and that they travel in straight lines

Dmitri Mendeleev

Mar 6, 1869

Created the first model of the Periodic Table of the Elements. While it did not contain all elements, it is what we work off of today.
[www.wikipedia.com/wiki/dmitri_mendeleev]
Image:http://scientistsinformation.blogspot.com/2011/01/dmitri-mendeleev-1834-1907.html, http://www.bpc.edu/mathscience/chemistry/history_of_the_periodic_table.html

Niels Bohr

Nov 25, 1885

Bohr was a Danish physicist who created the common Bohr Model. He made heavy contributions to everyday knowledge of atomic structure and quantum theory. http://en.wikipedia.org/wiki/Niels_Bohr

Erwin Shrödinger

Aug 12, 1887

1887 - 1961 Schrodinger was an Austrian physicist who contributed quite a bit to quantum physics and mechanics. His quantum model allowed people to calculate where electrons might appear. Shrödinger is also well known for his experiment, "Shrödinger's cat". http://upload.wikimedia.org/wikipedia/commons/1/1f/Schrodinger.jpg

J J Thomson

Nov 25, 1897

Thomson held a magnet to the Crooke’s tube, bending the light, showing that there were negative particles because they were attracted to the positive magnet. These particles were caled electrons. He created the plum-pudding model, because there were negative electrons spread throughout a positive field.

Enrico Fermi

Nov 25, 1901

Worked on the first nuclear reactor, and made heavy contributions to the quantum theory, particle and nuclear physics. Also known as the “father of the atomic bomb”. http://en.wikipedia.org/wiki/Enrico_Fermi

Einstein

May 11, 1905

Einstein's Brownian motion theory allowed scientists to find the average motion of a liquid. It also allowed scientists to find the size of atoms, verifying their existence.
[http://ansnuclearcafe.org/2012/03/20/albert-einstein-and-the-most-elemental-atomic-theory/]
Image: https://en.wikipedia.org/wiki/Albert_Einstein,https://upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Stylised_Lithium_Atom.png/200px-Stylised_Lithium_Atom.png

Rutherford

Jan 1, 1911

Created the nuclear model, which had a positive nucleus and a negative field around it. He also said that the nucleus was a lot larger than the electrons in the negative field. He found this by firing particles at a thin gold plate, and watching the particles bounce back from the nucleus.

HGJ Mosely

Nov 25, 1913

Developed the concept of the Atomic Number, which we use regularly today. http://en.wikipedia.org/wiki/Henry_Moseley

R.A. Millikan

Nov 25, 1917

Sprayed water and oil on ionized plates, and found that atoms that touched electrons floated up. Then was certain that electrons were 1000 times smaller than atoms(Thompson’s theory)
http://library.thinkquest.org/C006669/data/Chem/atomic/development.html

De Brogile

Jan 1, 1929

Theorized that electrons are also waves
[http://www-history.mcs.st-and.ac.uk/Biographies/Broglie.html,http://the-history-of-the-atom.wikispaces.com/Louis+de+Broglie]
Image:http://the-history-of-the-atom.wikispaces.com/Louis+de+Broglie,http://www.nobelprize.org/nobel_prizes/physics/laureates/1929/

Werner Heisenburg

Nov 25, 1932

Submitted 3 papers on a new neutron/proton model of the nucleus. Found that electrons do not move in set paths, which was part of his uncertainty principle. [wikipedia, the-history-of -the -atom.wikispaces.com]

Chadwick

Nov 25, 1932

Chadwick - 1932 Chadwick discovered neutrons by doing the joilot-curie experiment