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Period: 500 BCE to
Atomic Model
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442 BCE
Democritus
(460 BC- 370 BC)
Credited with 1st idea of Atoms; Believed atoms were indestructible -
430 BCE
Historical Event
Peloponnesian War begins -
Dalton
(1776-1844)
Confirmed that all matter is made up of atoms;
Thought that atoms were indestructible (false);
Said that atoms of the same element are identical (false);
Atoms of different elements differ in mass and other properties; When atoms of different elements combine to form compounds new and more complex particles form atoms in a given compound are always fixed in the same ratio. -
Historical Event
Louisiana Purchase -
Thomson
(1856-1940)
Discovered the electron; the plum pudding model said that electrons were floating around the model. -
Historical Event
Theodore Roosevelt becomes president -
Historical Event
The Boy Scouts of America founded -
Rutherford
(1871-1937) Discovered the nucleus of an atom; he said a nucleus is in the center of an atom with positive charges and most of the atom is empty space. -
Bohr
(1885-1962) Said that the nucleus was small and positively charged and was orbited by negatively charged electrons -
Historical Event
World War I begins -
Historical Event
The stock market crash of 1929 and start of The Great Depression -
Chadwick
(1891-1974) Discovered the Neutron; Found that the mass of the neutron is equal to the mass of the proton
