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332
Aristotle
*332 B.C.-Approximate date
Aristotle disagreed with Democitus' theory that all matter was made of small particles. He believed that everything was made up of each of the four elements: water, fire, air, and earth. -
460
Democritus
*460 B.C.
Democritus was the first scientist to suggest that all matter was made of atoms(atomos), which were small, indivisable, and indestructable. -
Antoine Lavoisier
Lavoisier created the law of conservation of matter. This law states that mass is never created or destroyed. -
Joseph Proust
Proust came up with the law of definite proportions, which states that chemical compounds contain the same proportions of their elements by mass. -
John Dalton
Dalton created the Atomic Theory, which states that: all matter is made of atoms; atoms are identical in their properties if they are the from same element; when chemicals rearrange it causes a chemical reaction; and when two or more different kinds of atoms are combined it creates a compound. He also created the spherical model; which shows that the atom is a circle. -
J.J. Thomson
Thomson did the cathode ray tube experiment. He placed cathode tubes in magnetic and electric fields. In his experiments, the cathode rays bent to one side, which was unusal and led Thomson to hypothesize that the cathode rays were made of a small particle. This led to his discovery of the electron. He also created the Plum Pudding Model; which shows electrons scattered in a positive atom. -
Max Planck
Planck created the Quantum Theory. This theory descirbes how energy is delivered in small packets called "quanta" when scientists did experiments using heated black surfaces. -
Ernest Rutherford
Rutherford is credited with discovering the nuclues of an atom and protons. He did experiments that showed when alpha particles were put into gas atoms, a few were deflected.This showed that atoms had a positively charged middle, which holds most of the atomic mass.Rutherford also did the Gold Foil Experiment.This experiment included firing radioactive particles through thin gold foils. He realized that some particles were deflected. This led him to believe that the atom was not only empty space -
Niels Bohr
Bohr created the Bohr model. When an atom gains enegry, electrons move a level farther away from the nucleus. When energy leaves, electrons move a level closer to the nucleus. -
Erwin Schrodinger
Schordinger created the Quantum Mechanical Model. Schrodinger used math equations to predict the odds of of the location of the election. The model shows where the electron cloud is most dense; which means the probability of finding an electron there is higher. It also shows where it is less dense; which is where the probability is lower. -
Werner Heisenberg
Heisenberg created the uncertainty principle. This states that position and momentum cannot be measured at the same time with high precision. Heisenberg states,"The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa." -
James Chadwick
Chadwick coppied experiments done by Frederic and Irene Joliot-Curie in order to find neutral particles. He was successful and discovered the neutron. He also made the modified nuclear model.
