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Period: 400 BCE to
The very very very long historic timeline of the atom
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450
Democritus
Democritus was a Greek philosopher who wondered what would happen if you cut a piece of matter into smaller and smaller pieces. He thought that a point would be reached where matter would be cut so small it could no longer be cut. He called these "uncuttable" pieces atomos, and this is the very beginning of the long history of the atom. -
John Dalton
In 1800, John Dalton would start to experiment with different gases to find their pressure, and during his experiments Dalton decided that gasses have to be made out of tiny particles constantly in motion. This would to Daltons 3 ideas the consist of his atomic theory.
Although his theory was accepted, Daltons was wrong about exactly what atoms were. Dalton thought Atoms were just tiny solid particles of matter, he didn't know atoms consisted of smaller particles. -
Amedeo Avogrdo
In 1811, Amedeo Avogrdo proposed what is now known as Avogadro's Hypothesis in 1811. The hypothesis states that at the same temperature and pressure, equal volumes of gases contain the same number of molecules or atoms. Although at the theory was rejected at the time, it became excepted after his death. -
Wilhelm Roenburg
In 1895, Wilhelmina Roentgen was experimenting with the effects of cathode rays. His experiments involved the passing of electric current through gases. While working he discovered that the screen he was working with would become illuminated when the Rays passed though. He would continue his experiments with a photographic plate to capture images of objects placed in the path of the Rays. These would be the first X-rays. -
JJ Thomson
In 1897, JJ Thomson created an experiment that would lead to the discovery of the electron. Thomsons experiment was him passing an electric current through a vacuum tube. The current would always pass through the negative plate into bending towards the side of the positive one. This didn't only show electricity was negatively charged, but it was carried by small particles of matter.
Thomsons Plum Pudding Model
Thomsons Experiment -
Earnest Rutherford
Earnest Rutherford in 1911, would discover something that would change the way the atom would be viewed and further the atomic age. Rutherfords discovery was the nucleus, and he did this by firing alpha particles at a piece of gold foil. After seeing most of the particles go through, then seeing a few bounce of in different directions, Rutherford then concluded the positive charge of an atom is contained in a small center called the nucleus.
Foil Edperiment -
Neils Bohr
The discoveries of the electron and radioactivity at the end of the 19th century would led to different models of the atom. In 1913, Niels Bohr had theory for the hydrogen atom, based on quantum theory. Electrons should move around the nucleus but only in certian orbits. When jumping from one orbit to another with lower energy, a light is emitted. Bohr's theory could explain why atoms emit light in fixed wavelengths.
Bohrs Model
