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400 BCE
Democritus
Democritus made up the theory of “atomons”, which were invisible, incompressible, solid and indivisible particles. He said that, actually, the only thing that exists in the Void (space) are atoms. He also said they were in constant random motion, which has been proved to be true thanks to the corpuscular-kinethic theory. -
John Dalton
He brought Demotricus' theory back, saying that different elements are made up of atoms that change in size and weight, but the atoms of a single element are all the same (Law of Multiple Proportions). -
Henri Becquerel
Becquerel discovered radioactivity when he left Uranium with no exposure to the Sun, but it still emitted radioactive rays. He also discovered that atoms could be divided. Moreover, radioactivity could be used to see the interior of an atom. -
Joseph John "JJ" Thomson
Thomson discovered that atoms have negative subatomic particles (what we know now as electrons). Thomson’s atomic model represented electrons in a positively charged matter. -
Marie Curie
She continued Becquerel’s work, discovering two new radioactive elements: radium and polonium. -
Ernest Rutherford
Rutherford discovered that atoms weren’t as people thought back then (Thomson’s model), but actually they had a positively charged nucleus with electrons around it. He based this on the gold foil experiment, which consisted in hitting a sheet of gold with alpha particles (positively charged). As expected, some went through it, but others went in different angles, even bouncing backwards. This explained the positive charge of atoms. -
Niels Bohr
Bohr completed Rutherford’s work, by adding that electrons orbit in specific orbits, just like planets orbit around the Sun. -
Robert Millikan
Millikan measured the electric charge of an electron with an “oil-drop” experiment. It was originally made with water, but due to its quick evaporation, it was changed to oil. -
James Chadwick
Chadwick discovered the neutron, a neutrally charged subatomic particle next to the proton in the nucleus. Its existence had been doubted before, but he was the one who proved it. -
Louis de Broglie
Louis thought subatomic particles (like electrons or protons) could also be waves instead of particles, by how the electrons were reflected against crystals. -
Erwin Schrödinger
Schrödinger created a new atomic model. Electrons move around the nucleus in “orbitals” (wave-like orbits) instead of simple circular orbits. -
Werner Heisenberg
Heisenberg discovered the “Uncertainty Principle”. It states that the position of an object can’t be known exactly.
