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450 BCE
Democritus Creates the First Atomic Model
In 450 BC, Greek philosopher, Democritus, proposed the first atomic model and theory. He did this by cutting stone into extremely small pieces called atomos, or atoms. He said these atoms were indestructible, solid, and invisible. His model was of a round sphere with no protons, neutrons, or electrons. -
Period: 440 BCE to
The History of the Atom
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Dalton Investigates Democritus's "Atom"
While working with gases, chemist John Dalton came to the realization that every form of matter (solid, liquid, or gas) is made of small particles. He came up with his own Atomic theory. His ideas included the fact that all atoms of the same element are alike and that atoms of different elements make different compounds. -
Thompson Accidentally Discovers Electrons
One day English scientist J.J. Thompson was experimenting with gas discharge tubes and electricity. During his experiment, Thompson noticed that there was a movement of particles. These particles moved to the positive end of the tube. Thompson came to the conclusion that these were negatively charged particles. These particles a best known as electrons today. -
Rutherford's "Gold Foil Experiment" is conducted
Rutherford's Gold Foil Experiment is very cruicial to the History of the Atom. In this experiment, Rutherford used a sheet of gold foil and shot positively charged particles at it. Some particles went through the foil and some bounced off of the foil. This told Rutherford that the nucleus was positive. He also discovers that atoms were mostly empty space. The particles that went through the foil told Rutherford that the Atom had a lot of empty space. This debunked previous thought. -
Bohr Proposes His Atomic Model
Danish physicist Niels Bohr proposed a planetary model of an atom. He proposed the idea that electrons revolve around the nucleus of an Atom like the planets revolve around the sun. His model included "levels" of electrons consisting of eight electrons each. If electrons lose energy they go down an electron level. If electrons gain energy they go up a level. Bohr was a main contributor of the Atom and he influences what Atom models look like today. -
Schroedinger and Hieserberg Amplify Bohr's Model
In 1926, Schroedinger and Hieserberg furthered Bohr's studies on electrons and amplified them. They used mathematical equations to find the likelihood of finding an electron in a certain position. This predicts the odds of the location of the electron. Where the electron cloud is more dense, the probability of finding is greatest. This process and model is known as quantum mechanical model of an atom.
