Atomic Theory Sophie Lum


The Greek Model- 400 BC

A Small Solid Sphere

Democritus' theory was that atoms are small objects that cannot be divided, created, or destroyed. He believed that atoms are constantly moving. He also believed that different types of matter are made from different atoms. The properties of the atoms he believed were determined by the properties of matter.

John Dalton

The Billiard Ball Model- 1802

A Small Solid Ball

Dalton, like Democritus believed that all matter is made from atoms that cannot be divided, created, or destroyed. He believed that suring a chemical reaction that atoms of one element cannot convert into one atom of another element. He said that atoms of one element are identical but are different from atoms of another element. He believed that atoms could only combine in specific ratios

J.J. Thompson

Plum Pudding Model- 1897

Resembles a chocolate chip cookie

Thompson discovered that the atom wasn't a solid ball because there was negatively charged particles, electrons, in the atm along with the positive protons. He called it the Plum Pudding Model because the electrons are like the chocolate chips in a cookie, while the protons make up the rest of the cookie as the "dough" or "pudding".

Ernest Rutherford

Planetary Model- 1909-1911

The atom has electrons orbiting around the nucleus

Rutherford discovered that the atom has a positive nucleus in the center along with negative electrons that orbit it. He discovered all of this through The Gold Foil Experiment. In which he would fire positive alpha protons at a sheet of gold foil. The particles would either go through the foil or bounce off into a different direction.

Niels Bohr

Bohr's Atomic Model- 1913

Bohr discovered that subatomic particles move around the nucleus in a circular orbit. He also found that if energy gets added to an electron then it will move farther away from the nucleus and to a higher electron level. If energy gets taken away from an electron then it will move closer to the nucleus and be on a lower electron level.

Erwin Schrodinger & Louis de Broglie

Electron Cloud Model- 1923 & 1930

Electrons are in a very fast moving "cloud"

The Electron Cloud Modle is the modern atomic modle. Schrodinger discovered that there were waves of electrons which to find the exact location which created a long and complicated calculation. Broglie wrote a thesis about the Quantum Theory that was confirmed to be true by the discovery of the electron.

James Chadwick

Neutrons- 1932

In 1932, James Chadwick discovered that atoms contained something called neutrons. Neutrons are the third kind of subatomic parti la and they have no charge, they are neutral hence the name.

Atomic Theory Timeline

  • 400 BC ~ The Greek Model by Democritus
  • 1802 ~ Billiard Ball Model by James Dalton
  • 1897 ~ Plum Pudding Model y J.J. Thompson
  • 1909-1911 ~ Planetary Model by Ernes Rutherford
  • 1913 ~ Bohr's Atomic Modle by Niels Bohr
  • 1925 ~ Electron Cloud Theory by Erwin Schrodinger and Louis de Broglie
  • 1932 ~ Neutrons Discovered by James Chadwick

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