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400 BCE
Democritus
He was the first one to discover that all things are made up of things called ‘atoms’ which he got from the Greek word ‘atomos’ which means uncuttable. His theory of atoms were a round ball which could not be broken, he did not know of any electrons, protons, neutrons or the nucleus which didn’t give him many ideas of what an atom could be made of. -
350 BCE
Aristotle
Aristotle disagreed with democritus' model and had an entirely different idea of it himself. His ideas weren't scientifically based, they were thought based. The thought that there was no smallest part of matter, but instead thought that different substances were made of water, fire, earth and air. He didn't have an atomic model because the didn't think that they existed. -
Antoine Levoisier
Lavoisier was the first creater of the periodic table and expanded on Aristotle's theory of the 4 elements (fire, water, earth and air). By using the previous knowledge of atomic bonding, he discovered important elements like oxygen, hydrogen and solfur. He discovered that water was made up of oxygen and hydrogen and air was made up of nitrogen. -
John Dalton
John Dalton was an English chemist that created the Atomic Theory of Matter, a mix of previous findings by Democritus and his own findings. His theory said that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine to form chemical compounds. His theory would later contribute and help to advance in the atomic model. -
Henri Becquerel
Henri Becquerel family were scientists. With influences from his father and grandfather, Bequerel worked with properties of the atom, such as magnetism and radioactivity. He discovered more in radioactivity. When he was younger, he worked with light and light through crystals. He also looked at the mechanics of X-Rays. His work on radioactivity helped scientists later to perfect the atomic model. -
J.J Thomson
J.J. Thomson was a very important scientist when it came to the atomic model. All the theories of the atom before him were a solid ball, he discovered the electron, which led him to make the 'plum pudding' model. In this model, he thought that the atom was mostly positive, and the negative electrons floated around the atom. -
Marie and Pierre Curie
Marie and Pierre were a European couple that was working on radioactivity. After Henri Baquerel first discovered radioctivity, Marie decided to look further into this discovery. Her and her husband discovered the elements radium and polonium and won the nobel Peace prize for their works in radioactivity. Her discovery later added to the atomic model. -
Max Planck
Max Planck was a German scientist that discovered the Quantum theory. He said that energy was given off in little packets of energy. They were called photons when talking about light. He also discovered that the energy in wave form is restricted to specific amounts. This led to the understanding of energy levels in atoms, since quantums are leaps in the atom. This discovery later helped advance the knowledge of the atom. -
Robert Millikan
Robert Millikan was an American scientist that was interested in J.J Thompson's theory. J.J Thompson said that the electron was 1000 times smaller than the atom. Millikan wanted to prove this. He performed an oil-drop experiment to prove J.J Thompson's theory and it worked. He also involved the Quantum theory from Max Planck's theory. He inspired other scientists to explore parts of the atom. -
Ernest Rutherford
Ernest Rutherford was another scientist that changed the atomic model. He felt that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. This model influenced one of his own students to perfect the atomic model later on. -
Niels Bohr
Niels Bohr was a Danish scientist that was a student of Ernest Rutherford. He decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom. Bohr also used Planck's ideas in order to create quantum mechanics, his new concept regarding energy. This model is still used to this day. -
Henry Mosely
Henry Mosely was an English scientist who worked with Niels Bohr in order to create the real atomic number. Mosely used X-rays to find the frquencies of elements on the periodic table. Before his discovery, the atomic number was just an random number to a random element. Mosely used these frequencies to find that the number of protons in the nucleus was the atomic number. This created Mosley's Law. -
Erwin Schrodinger
Erwin Scrhodinger was an Austrian scientist that worked with the Quantum model of the atom. He disagreed with Bohr's theory, so he created his own. He thought that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus. This equation helped create the Quantum mechanical model of the atom. -
Werner Heisenberg
Werner Heisenberg was a German scientist that questioned the uncertainties of the Quantum model. He said that you can't know the exact height and speed of the electron at the same time, which means you can't know the exact location of the electron. This theory proves Bohr's model wrong because of the uncertainty of the location of an electron. -
James Chadwick
Jame Chadwick was an English scientist that discovered the neutron. Before this discovery, Rutherford had said that the nucleus was made of positive matter. It made sense that the atom was neutral because the negative electrons and the positive protons cancelled out. But, Chadwick started to question why there was a difference between the atomic mass and the number of protons. Chadwick then found that the missing part was a neutral part: the neutron.