PRESENTATION OUTLINE
Empedocles
-440 BCE
-He is attributed to the invention of the four element theory of matter (earth, air, fire, and water). He believed that these elements were able to create all things, living and nonliving, by being mixed together.
Democritus
-492 BCE
--He was the first to propose the atomic theory and he created the word atom from the Greek word "atomos."
Aristotle
-350 B.C.
-He felt that regardless of the number of times you cut matter in half, you will always end up with a smaller piece of it. He did not believe there was a smallest piece of matter.
Evangelista Torricelli
-1644
-He discovered that air has weight and can push down a column of mercury.
Daniel Bernoulli
-1738
-He suggested the existence of grain-like atoms flying around in empty space.
Joseph Priestly
-1774
-He discovered oxygen. He originally called his discovery "dephlogisticated air."
Antoine Lavoisier
-1785
-He proposed the Law of Conservation of Mass (1785). He also identified 23 elements which he believed could not be broken down into simpler substances (1789).
Joseph Louis Proust
-1799
-He proposed the Law of Constant Composition. His was a very radical idea at his time and was often debated.
John Dalton
-1803
-He developed Dalton's Atomic Theory. It stated that matter is composed of atoms.
Michael Faraday
-1832
-Studied the effect of electricity on solutions
-Came up with the term "electrolysis" as a splitting of molecules with electricity, and also developed the laws of electrolysis.
Henri Becquerel
-1896
-Discovered some chemicals spontaneously decompose and give off penetrating rays.
J.J. Thompson
-1897
-He discovered the electron while experimenting with a cathode-ray tube.
Marie and Pierre Curie
-1898
-Theorized that radioactive particles cause atoms to break down.
-Studied uranium and thorium and called their decay process "radioactivity".
-Discovered the radioactive elements polonium and radium.
Ernest Rutherford
-1899
-Used alpha particles as atomic bullets and had the atoms in a piece of gold foil, this was the gold foil experiment. He developed the theory for the structure of the atom.
-First referred to the hydrogen nucleus as a proton.
-He also proposed the existence of the third atomic particle, the neutron.
-Assumed the electrons were outside the nucleus.
Max Planck
-1900
-Introduced the Quantum theory: electromagnetic energy could only be emitted in quantized form.
-He used the idea of quanta (discrete units of energy) to explain hot glowing matter.
Albert Einstein
-1905
-Created both special and general theories of relativity, and also hypothesized about the particle nature of light, which was the basis of nuclear energy.
Robert Millikan
-1909
-Discovered the unit charge of the electron with his oil drop experiment. This charge is known as the elementary charge.
-Allowed for the calculation of the mass of the electron and the positively charged atoms.
Niels Bohr
-1922
-Developed an explanation of atomic structure that has to do with the regularities of the periodic table.
-Has an atomic model (Bohr atomic model) that has atoms built up of successive orbital shells of electrons.
Louis DeBroglie
-1924
-Did research on quantum theory and discovered the wave nature of electrons.
Ernest Schrodinger
-1930
-Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.
James Chadwick
-1932
-He discovered a neutral atomic particle with a mass close to a proton, so he discovered the neutron.
-This discovery of the neutron led to the discovery of fission and ultimately to the atomic bomb.
