Atom Timeline

Events

Democritus Classical Era In Greek

Approx. 400 BC

Believed the atom are hard solid circular and invisible.
Facts :He was a philosopher

John Dalton Industrial Revolution Lived In United States

1803

5 Theory
No subatomic particles/indivisible atoms
Most of his principles were right, he just didn't know about neutrons/isotopes
Said atoms of same element have same mass (NOT true because isotopes!)
Fun Fact:He identified the hereditary nature of red-green color blindness.

Dmitri Mendeleev lived in Russia

1869

Discover the Periodic Table, Pycnometer, and Pyrocollodion.
Fun Fact: Russian chemist and inventor

JJ Thomas Lived In the United Kingdom

1897

Discovered electron Used cathode-ray tube
Plum pudding model -- electrons evenly distributed throughout the model.
Fun Fact:In 1908 he was knighted for his contributions to science and in 1912 he received the Order of Merit.

Robert Millikan Lived In United States

1909

Discovered charge of an electron using oil drop apparatus
Fun Fact:When measuring the course of charged water droplets, they evaporated too quickly

Ernest Rutherford Lived in Canada, Nelson,England

1911

Gold foil experiment Discovered nucleus Nucleus very dense and it is positive.
Fun Fact: Element 104, rutherfordium, is named after him.

Aage Bohr Lived in Copenhagen

1912

Discovered electron's circular orbit explained the bright line emission spectrum with his planetary model.
Fun Fact: In April 1940, when Aage was 17, Denmark was invaded by the armed forces of Nazi Germany.

Henry Moseley Lived in Weymouth

1914

There was a repeating pattern to the properties of elements
Arranged the elements by increasing atomic mass.
Fun Fact:He was the first to use X-ray spectroscopy to measure the X-ray spectra of metals which was important in the invention of X-ray crystallography.

Werner Heisenberg Lived in Würzburg

1925

Modern atom interpretation: fuzzy cloud electron's whereabouts can only be known on average electron's position and momentum cannot be known at same time.
Fun Fact:His later work included study of plasma physics and the process of nuclear fusion.

James Chadwick lived in United States

1932

The properties and structure of atomic nuclei, specifically the neutron.
Determined that some "strong force" holds the nucleus together, a force distinct from the electromagnetism.
Fun Fact:In 1945, the British Government knighted him for his wartime contribution, and he became Sir James Chadwick.

Fun Fact
:Prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb.