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400 BCE
Democritus
460 BCE – 370 BCE
Democritus proposed that matter is composed of small, indivisible particles called "atomos," or atoms. This was the first concept of the atom, setting the foundation for atomic theory. -
Louisiana Purchase
The United states of America purchased the Louisiana territory from the French, doubling the size of their country -
John Dalton
September 6, 1766 – July 27, 1844
Dalton introduced the idea that atoms of different elements have different masses, creating the “marble” model, which proposed that atoms are solid, indivisible spheres. This helped establish the first modern atomic theory. -
Michael Faraday
September 22, 1791 – August 25, 1867
Faraday’s work with electricity and magnetism introduced the idea that atoms could interact through forces, laying the groundwork for atomic behavior and bonding theories. -
Eugene Goldstein
September 5, 1850 – December 25, 1930
Discovered canal rays (positively charged particles), contributing to the understanding that atoms contain subatomic particles. -
Spanish-American War
The Spanish–American War began in the aftermath of the internal explosion of USS Maine in Havana Harbor in Cuba, leading to United States intervention in the Cuban War of Independence. -
JJ Thomson
December 18, 1856 – August 30, 1940
Thomson discovered the electron, proposing the "plum pudding" or "chocolate chip cookie" model, where electrons are embedded in a positively charged sphere, introducing the concept of internal structure within atoms. -
Robert Millikan
March 22, 1868 – December 19, 1953
Millikan’s oil drop experiment determined the charge of the electron, providing essential data for understanding atomic structure. -
Ernest Rutherford
August 30, 1871 – October 19, 1937
Rutherford discovered the nucleus, creating the “nuclear” model with a dense, positively charged core and electrons orbiting around it. This shifted the understanding of atomic structure dramatically. -
Neils Bohr
October 7, 1885 – November 18, 1962
Bohr developed the “solar system” model, proposing that electrons orbit the nucleus in specific energy levels, which explained atomic stability and spectral lines. -
Period: to
WWI
World War I or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. -
Edwin Schrödinger
August 12, 1887 – January 4, 1961
Developed the “electron cloud” model, describing electrons in probabilistic orbitals rather than fixed orbits, leading to the quantum mechanical model of the atom. -
Werner Heisenberg
December 5, 1901 – February 1, 1976
Heisenberg’s Uncertainty Principle introduced the idea that one cannot simultaneously know both the position and momentum of an electron, reinforcing the probabilistic nature of atomic behavior. -
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The Great Depression
The Great Depression was a period of severe global economic downturn that occurred from 1929 to 1939. It was characterized by high unemployment rates, crisis of liquidity, and widespread business failures around the world -
James Chadwick
October 20, 1891 – July 24, 1974
Chadwick discovered the neutron, which led to the refinement of the electron cloud model by adding neutrons in the nucleus, explaining isotopes and atomic mass more accurately. -
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WWII
World War II or the Second World War was a global conflict between two coalitions: the Allies and the Axis powers.