-
350
Aristotle
Aristotle did not believe in the atomic theory, he believed all materials were made up of 4 elements. The elements were, earth, fire, water, and air. He believed all substances on earth were made up of these elements. -
400
Democritus
Democritus was the first person to create an atomic theory. His theory was that all matter consists of atoms that are invisible. Atoms can not be destroyed and they are solid but invisible. These particles are homogenous. He also believed that atoms differ in size, shape, mass, position, and arrangement. -
Robert Boyle
Robert boyle discovered that elements can be combined together to form compounds. -
Lavoisier
Lavoisier defined elements as pure substances that can be decomposed, He also developed a system for naming chemicals so that all scientists could use the same words. Lavoisier identified 23 more pure substances as elements and discovered that in a chemical change the mass of the new substance is always the same as the mass of the original substances (laws of conservation of mass). This was between 1770-80. -
John Dalton
John Dalton believed that all matter is made up of small, indestructible, solid and homogenous particles called atoms. He believed that all atoms of a given element are identical in mass and properties. He also believed that compounds are created when atoms of different elements link together. -
Dmitri Mendeleev
Dmitri Mendeleev made the periodic law. He arranged elements into groups. He arranged them in 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights." -
Eugene Goldstein
Eugene Goldstein used Cathode ray tube to study canal rays. They had electrical and magnetic properties which are the opposite of an electron's electrical and magnetic properties. -
G.J. Stoney
G.J. Stoney suggested that electricity is made up of electrons. -
Henri Becquerel
Henri was studying the effect of x-rays on film. Henri later discovered that some chemicals decompose and give off very strong rays unplanned (and sudden). -
J.J Thomson
J.J Thomson figured out the charge to mass ratio of an electron. -
Marie Curie
Also studied uranium and thorium like Rutherford. She called uranium and thoriums’ spontaneous decay process "radioactivity". She and her husband also discovered other radioactive elements polonium and radium. -
Soddy
Soddy watched unplanned (and sudden) disintegration of radioactive elements into versions he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during the decay. -
Max Planck
Explained hot glowing matter. -
Albert Einstein
Came up with equation E=mc^2 which means energy=mass*speed of light^2. -
Millikan
Worked on oil drop experiment in which he figured out the charge of one electron. -
Ernest Rutherford
Rutherford was using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the center of a cell or atom was: very dense,very small and positively charged. He also assumed that the electrons were located outside the center of a cell or atom. -
Moseley
Moseley used x-ray tubes to figure out the nucleus of most atoms. He wrote that “the atomic number of an element is equal to the number of protons in the nucleus." This reorganized the periodic table. Moseley’s work made the periodic table based on the atomic number instead of the atomic mass. -
Aston
Aston discovered the existence of isotopes. He discovered it through the use of a mass spectrograph. -
Niels Bohr
Developed an explanation of atomic structure. -
Heisenberg
Heisenberg Proposed the Principle of Indeterminacy - you can not know both the position and velocity of a particle. -
Erwin Schrödinger
Formulated a wave equation. This equation accurately gave the energy levels of atoms. -
James Chadwick
In 1932, James discovered the neutron. -
Otto Hahn
Otto Hahn Did experiments proving that heavy elements capture neutrons and they form unstable products. The unstable products go through fission. This process ejects more neutrons continuing the fission (when A causes B, which causes C, etc.). -
Glenn Seaborg
Created six transuranium elements. He also suggested a change in the layout of the periodic table. -
Period: to
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