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415 BCE
Democritus
In between, the years 460-370 BC, a philosopher and scientist by the name of Democritus proposed the atomic theory. Democritu's foundation for his atomic theory, stated that,- "The universe is composed of two elements: the atoms and the void in which they exist and move.” He aslo belived that the universe was made of miniscule quantities of matter, that were the essential components of the entire universe, "Atoms." Although his theory had a scientific basis, present society rejected his ideas. -
Period: 415 BCE to
The History of the Atom
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John Dalton
Almost 2218 years after Democritus proposed his, Atomic Theory, a scientist by the name of "John Dalton", expanded on Democritus's theory regarding Atoms and its "application" and presence in the universe. Dalton's "expanded" theory, stated that, "All matter was composed of atoms, indivisible and indestructible building blocks." He also believed that, while all atoms of an element were identical, different elements had atoms of differing size and mass. Dalton also proposed the, Hard sphere model -
J.J. Thomson
In 1897, a physicist by the name of J.J. Thomson "discovered" the existence of electrons, by experimenting with a cathode ray tube. As electrons carry negative charges, this affected the cathode tube, by providing it with a negative charge. He also created a new atomic model, called,"The Plum Pudding model". In this model, the atom is a sphere of positive charge, and negatively charged electrons are embedded in it to balance the total positive charge. -
Ernest Rutherford
In 1911, a physicist named Ernest Rutherford, discovered the existence of the nucleus within the centre of an atom through an experiment. In his experiment, Rutherford had a device discharge a beam of alpha particles at a sheet of gold; and tried to test if any of these particles were reflected or refracted. Through the analysis of his results, he found that there was "something" that reflected the alpha particles within the atom; and "that" had electrons "around" it: this was the nucleus. -
Niels Bohr
Niels Bohr was a student of Ernest Rutherford and noticed some errors in Rutherford's atomic model. Rutherford's model had the electrons orbiting the nucleus, however scientifically it was later proven that if the electrons were orbiting the nucleus, and lost energy, it would collapse and instability. Bohr proposed that these electrons could "jump" from shell to shell through the empty space rather than collapsing. He later developed a new model named the Quantised shell model. -
Erwin Schrödinger
In 1926, Erwin further advanced Bohr's Quantised Shell model, by creating an equation that could determine the likelihood of the position of an electron. This allowed Erwin to formulate and understand that the electrons did not necessarily orbit the nucleus via shells, but instead were within separate "clouds" around the nucleus of an atom. This eventually lead to him developing the Electron Cloud model of the atom.
