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460 BCE
Democritus
Democritus is best known for the Atomic Theory. His mentor Leucippus originally came up with the atomic theory, but Democritus eventually took it over. The atomic theory said" The universe is composed of two elements: The atoms and the void in which they exist and move." Democritus stated in the atomic theory that all matter consists of small particles called atoms, Atoms are are indestructible, solid but invisible, homogenous, and atoms differ in shaper, size, mass, position, and arrangement. -
340 BCE
Aristotle
Aristotle gave us knowledge about Physics. He didn't believe in the Atomic Theory. He didn't believe that elements could constantly being moving in a void. He believed that there were 4 elements to life that made up all matter, air, water (he believed was wet), earth (he believed was cold), fire (he believed was hot). His theory was proven wrong because many more elements have been discovered since then, but Aristotle did prove the fact that there elements make up matter and everything in life. -
Antoine Lavoisier
Lavoisier is best known for discovering the Law of Conservation of Matter, which states that matter can never be created or destroyed. He found out that mass is conserved in a chemical reaction.This means during any chemical reaction the total mass at the beginning of the reaction must be the same as the total mass at the end of the reaction. He figured out that water contains 2 hydrogen atoms and one oxygen atom.When chemically combined together it makes H2O, which is the still the same. -
John Daton
John Dalton realized that since all elements were made up of atoms that it was possible for elements to combine. He came up with a theory that stated that different elements were different from the same elements that are identical to each other, all particles of matter are made up of atoms and can't be created or destroyed, and that atoms chemically combine together to create new atoms defined in ratios. The simplest ratio of combined atoms was H2O, which was needed in order to create water. -
Henri Becquerel
Heri Becquerel is best known for discovering Radioactivity. He found out through his experiments that uranium salts emits rays that are similar to X-rays and the power that they have. He demonstrated that the radiation from the rays didn't depended on an external source of energy but came from the uranium itself which led to the conclusion that he had discovered Radioactivity. -
J.J Thompson
J.J Thompson proved John Daltons theory to be false. Thompson experimented with cathode rays which led him to discover that atoms are negatively and positively charged and that there are particles in every atom. The particles can be divided. He made a model of plum pudding (representation of an atom) which allowed advances to be made in the future. -
Marie & Pierre Curie
Marie & Pierre Currie carried on Henri Becquerels work with uranium. They worked to find more elements, which they successfully did discovering radium and polonium (named after Marie's home town). Marie carried on with radioactivity more than Pierre Curie but didn't make it very far. -
Max Planck
Max Planck is best known for coming up with the quantum theory, which was that light energy is radiated in packets/amounts rather than in a continuous unbroken wave. Planck was able to come up with an equation to determine the energy of each quanta (amounts/packets of energy). The formula is known as Planck's Constant. -
Robert Milikan
Robert Milikan conducted a famous oil drop experiment that measured the charge of an electron. He also measured the mass of an electron which is -1. He proved J.J. Thompsons hypothesis to be true which is the mass of an electron is 1000 times smaller than the lightest atom. -
Ernest Rutherford
Ernest Rutherford came up with an atomic theory that an atom is mostly composed of empty space. He also said that the nucleus is positively charged with protons, it contains the atomic mass, and its small and dense. He came up with a nuclear model. The inside pit is the nucleus and the outside is empty space that contains electrons randomly orbiting around the nucleus. Rutherford used the Gold Foil experiment to help come up with his atomic theories. -
Niels Bohr
Niels Bohr is most known for creating an atomic model of an atom called the Bohrs Model. Bohr changed the orbits of electrons compared to Rutherfords model. He also created energy levels, so only a certain amount of electrons can go on each shell. He said electrons travel around the nucleus in a definite path. He also stated that electrons can't travel between each path but they can jump from one path to another with a different atom. This model is still taught and used today. -
Henry Moseley
Henry Moseley experimented by shooting high energy electrons at different chemical elements and measuring the wavelengths and frequencies of the X-rays. He then discovered that each element has its own unique frequency and atomic number. He realized that the elements on the periodic table were arranged in order by atomic number instead of atomic mass. The atomic number gave the periodic table a better fit. -
Erwin Schrodinger
Erwin Schrodinger didn't agree with Bohrs model so he built upon Bohrs thoughts and made his own model. Its called the Electron Cloud Model. His model doesn't show where an electron is at at a certain time or what its energy is but it can predict where it should be. He thought the only way to find an electrons energy and location was to calculate how far away it was from the nucleus. -
Werner Heisenberg
Werner Heisenberg is best known for his uncertainty principal called the Heisenbergs Uncertainty Principal. In the principal he stated that it wasn't possible to know the energy/ speed and location of an electron or any other particle at the same time. By measuring one (energy/ speed), you changing the other (location).This proved Bohrs model to be wrong because Bohrs model showed the exact amount of energy and the exact location which Heisenberg said to be impossible. -
James Chadwick
James Chadwick is best known for discovering the neutron. He realized that the atomic mass was double the amount of protons, which was the neutrons.He bombarded beryllium atoms with alpha particles and an unknown radiation was produced (neutrons). He said that neutrons have no electrical charge and most of the time an atom had the same amount of neutrons as the protons.
