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405 BCE
World event within 10 years of Democritus’ discovery
The war between the Athenians and the Peloponnesians ended. -
400 BCE
Democritus
He discovered atoms in 400 BC.
Born: 460 BC
Died: 370 BC
Democritus discovered the atom and believed they were uniform, solid, hard, incompressible, and indestructible. He also believed that atoms moved in infinite numbers through space until they stopped. -
World Event within 10 years of Dalton’s discovery
End of the French Revolution. -
Dalton's Marble Model
Dalton called this model the marble model because he envisioned atoms as solid, hard spheres, so he used wooden, marble-like balls, in his model. -
John Dalton
Created the Atomic Theory in 1803.
Born: September 6, 1766
Died: July 27, 1844
Dalton’s discovery changed how scientists thought of atoms because he stated that elements consist of atoms, all atoms from the same element are identical, different elements have different types of atoms, and atoms cannot be created or destroyed.
“Matter is made up of solid marble-like particles (atoms).” -
Michael Faraday
Discovered the laws of electrolysis in 1833.
Born: Seprember 20, 1791
Died: August 25, 1867
Faraday’s discovery of the laws of electrolysis changed how scientists viewed atoms because he found a way to separate a molecule into its component atoms.
He did this by running an electrical current through water or another substance, and the substance would be separated into atoms, and it proved that atoms have an electrical component. -
Eugen Goldstein
Discovered the proton in 1886.
Born: September 5, 1850
Died: December 25, 1930
Goldstein changed the way that scientists thought about atoms by discovering the proton.
This was due to his “canal rays” experiment in which he used a cathode ray tube with holes in the cathode and noticed that rays were traveling in the opposite direction from the cathode rays. -
JJ Thomson
Discovered the electron in 1897 and created the "Plum Pudding" Model in 1898.
Born: December 18, 1856
Died: August 30, 1940
Thomson changed how scientists thought about atoms by discovering electrons. He discovered them with his experiment including a cathode tube. His experiment showed that all atoms contain tiny negatively charged subatomic particles (electrons). -
JJ Thomson's "Plum Pudding" Model
Thomson called it the plum pudding model because the electrons are distributed uniformly like raisins in plum pudding. -
World Event within 10 years of Thomson’s discovery
The Panic of 1907 - the first worldwide financial crisis. The New York Stock Exchange fell by almost 50%. -
Rutherford's "Nuclear" or "Jimmy Neutron" Model
This model is most commonly called the "nuclear model" because it is the first model to feature the nucleus at its core. -
Robert Millikan
In 1910, he found the charge of an electron.
Born: March 22, 1868
Died: December 19, 1953
Mililkan’s discovery changed how we thought about atoms by proving the existence of an electron and accurately determining the magnitude of one’s charge (negative charge). -
Ernest Rutherford
Discovered the atomic nucleus in 1911 and also created the "nuclear" model or the "Jimmy Neutron" model of an atom in 1909.
Born: August 30, 1871
Died: October 19, 1937
He discovered the nucleus from his gold foil experiment in which a beam of alpha particles was aimed at a piece of gold foil. Most of the particles passed through the foil but some were scattered backward showing that most of an atom is space surrounding a small nucleus. -
World Event within 10 years of Bohr’s discovery
The sinking of the RMS Titanic in the North Atlantic Ocean. -
Bohr's "Solar System" Model
It is called the "Solar System" model because it looks exactly like the solar system with electrons circling the nucleus instead of planets circling the sun. -
Niels Bohr
In 1913, he proposed that electrons orbit around the nucleus and created the "Solar System" model of an atom.
Born: October 7, 1885
Died: November 18, 1962
Bohr’s discovery of how electrons orbited around the nucleus changed how we thought about the atom because scientists were able to discover that the number of electrons in the outer orbit determines the properties of an element. -
Werner Heisenberg
Heisenberg formulated a type of quantum mechanics in 1925.
Born: December 5, 1901
Died: February 1, 1976
Heisenber’s discovery changed the way that scientists thought about the atom by formulating a type of quantum mechanics based on matrices and discovering the uncertainty principle.
The uncertainty principles state that a particle's position and momentum cannot both be known with perfect accuracy. -
World Event within 10 years of Schrödinger discovery
The death of stuntman Harry Houdini. -
Erwin Schrödinger
In 1926 he created a model that shows the area around an atom's nucleus where electrons are most likely to be found.
Born: August 12, 1887
Died: January 4, 1961
Schrödinger changed how scientists thought about the atom by formulating a wave equation that accurately calculates the energy levels of electrons in atoms.
The equation was: H ^ ψ = E ψ -
Schrödinger's "Electron Cloud" Model
It is called the "Electron Cloud" model because the cloud-like figure represents the many possible locations of an electron within a particular area. -
World Event within 10 years of Chadwick’s discovery
The Great Dust Bowl- severe dust storms in the US due to a drought. -
James Chadwick
Chadwick discovered the neutron in 1932 and added neutrons to the "electric cloud" model of an atom.
Born: October 20, 1891.
Died: July 24, 1774
Chadwick’s discovery changed the model of the atom by discovering neutrons and claiming that they are located in the nucleus of an atom.
His discovery changed the way that scientists thought about atoms because they realized that the neutron had a neutral charge and could be used to “probe” other nuclei. -
Chadwick's “electron cloud” model with neutrons added.
James Chadwick's version of "Electron Cloud".