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400
Aristotle
click here to learn about Aristotle's atomic theory400 BCE
Aristotle was a Greek philosopher who was widely consitered to be one of the greatest minds of all time. He believed that everything on earth was made of the "four earthly elements": earth, water, fire and air. This contradicts both the periodic table of elements (there are over 100 known elements today). It also contradicts the existence of the atom which every other scientist of the list has refuted. Aristotle bid not believe Democritus's atom theory. -
460
Democritus
click here to learn/see Democritus's atomic model 460 BCE
Democritus was an Ancient Greek philosopher (often known as the "laughing philosopher"). He came up with the first idea of the atom which contradicted Aristotle's idea of everything being made of either earch, fire, air or water. His model of an atom was a small spherical shaped particle that was the smallest piece of matter possible. Democritus believed that all atoms were made up of the same material, but they were different sizes. -
Antoine Lavoisier
French nobleman, Antoine Lavoisier is consitered to be the father of modern chemistry. He most notably discovered wo elements, hydrogen and oxygen. He also established that sulfur was an element and not a compound as well as predicting the existence of silicon. This model did not change from the previous one aside from simply adding another element -
John Dalton
English chemist, meterrologist and physicist, John Dalton, is best known for his work on atomic theory. He came up with the atomic theory-whic modern physical science is founded from. His theory stated that all matter was composed of small indivisible particles and these particles (atoms) of a given element are identical in size, mass, and other properties while atoms of different elements differ in size, mass, and other properties. -
Henri Becquerel
Henri Becquerel discovered radioactivity when conducting an experiment concerning the exposure of a uranium-bearing crystal to sunlight. After a certain amount of time in the sunlight, the crystal copied its image onto the plate, which Becquerel theorizsed to be a release of uranium through x rays due to the absorbed energy of the sun. This led to his discovery of radioactivity. Pierre and Marie Curie soon followed up with these findings -
J.J Thompson
J.J Thompson discovered the electron in the year 1897. He suggested that the electron was over 1,000 times smaller that the atom and proved this using cathode rays. He used this discovery of electrons (he called them "corpuscles") to create a new model of the atom. He called this model the "Plum Pudding" model because the electrons in the model floated around the positive energy such as plums floating in pudding. This model was later replaced by Niels Bhor's updated model of the atom. -
Marie & Pierre Curie
The Curies followed up on Henri Becquerel's work on radioactivity. They discovered that the amount of radioactivity emited from an atom depends on the atom's interior and not the arrangement of the mollecules (as previously believed by Becquerel). In their research, they also discovered two radioactive elements: radium and polonium. -
Max Planck
Max Planck introdced the hypothesis that energy is given/released in bundles called "quanta" rather than gradually as previously believed. This was the origin of the quantum theory which was later developed further by scientists such as Werner Heisenberg, Erwin Schrodinger, Niels Bhor and other scientists. He also thought up "Plancks Constant"; which was the relation between the energy and frequency. -
Robert Millikan
Robert Millikan, an American scientist, discovered the charge and mass of the electron throught the oil drop experiment. The experiment balanced the downward gravitational force with the upward drag and electric forces on tiny charged droplets of oil suspended between two metal electrodes. Throught this experiment, he concluded that the charge of a single electron was 1.602176487(40)×10−19 C. Millikan demonstrated the atomic structure of electricity. -
Ernest Rutherford
Ernest Rutherford worked under J.J Thompson at Cambridge and eventually succeeded Thomson as professor and director of the Cavendish Laboratory at Cambridge. Rutherford created a new model of the atom in which all of the mass was located in the center, thus discovering the nucleus. Rutherford noticed that alpha particles didn't always behave as predicted to Thompson's plum pudding model when launch at a piece of gold foil. His discovery corrected J.J Thompson's model. -
Henry Mosely
Mosely was an Englishman who began his research under Ernest Rutherford. Moseley studied the relationship between the bright line spectrum of different elements. He found that the frequency of the X rays emitted by each element when fed cathode rays had a correlation to the atomic numbers. Mosely found that the atomic number is the same as the charge of the nucleus (the number of protons) -
Niels Bohr
Click here to see and learn more about the Bohr Model! iels Bhor enhanced the previous atomic model by stating that the electrons moved around the nucleus in large orbits. He also created the Bohr model which stated that atoms absorb or give off radiation when the electrons quickly moved between stationary, states. This allowed Bohr to explain the stability of the nuclear model of the atom; something that Rutherford ouldn't do. He used quantum theory which originated from Max Planck. -
Werner Heisenberg
Heisenberg was a german scientist known for his theory of quantum mechanics. It was based entirely on what was observed from the radiation of an atom. He claimed that we can't always assign an electron a position in space at a given time, or follow its orbit, so we can't assume that the planetary orbits thought of by Niels Bohr exist. His principle of uncertainty stated that increasing the accuracy of measurement of one observable amount increases the uncertainty with with another known amount -
Erwin Shroedinger
click to see and learn more about the Quantum mechanical modelAustrian, Erwin Shroedinger created a wave equation that describes the form of the waves that control the motion of small particles/atoma and how these waves are affected by external factors. He helped explain the movement of an electron in an atom as a wave. This advancement took the Bohr model a step further by finding the likely hood of finding an electron in a certain position. This is called the Quantum mechanical model. -
James Chadwick
Click to see/learn about Chadwick's updated atom Chadwick proved the existence of neutrons (particles devoid of positive or negative charge). This discovery allowed him to make an updated model of the atom with both protons AND neutrons in the nucleus. James Chadwick also established the atomic number being the amount of protons in an atom.
