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322
Aristotle (322 B.C.)
He believed in the four elements of air, earth, water, and fire. He felt that regardless the number of times you cut a form of matter in half, you would always have a smaller piece of that matter. -
440
Democritus (440 B.C.)
Believed in 5 key ideas about the atom:
1. All matter is composed of atoms, which are bits of matter too small to be seen. These atoms cannot be further split into smaller portions.
2. There is a void, which is empty space between atoms.
3. Atoms are completely solid.
4. Atoms are small homogeneous, with no internal structure.
5. Atoms are different in their size, shape, and weight. -
Antoine Lavoisier
Invented the analytical balance and showed that elements could not be distroyed. -
Joseph Louis Proust
Found the law of definite proportions, stating that when compounds are analysed into their constituted parts they always contain the same proportions of their elements by weight. -
John Dalton
Found the atom to be the smallest particle of matter that takes part in a chemical reaction. He also proved it cannot be created or destroyed. -
Michael Faraday
He studied effects of electricity on solution. Also found the term electolysis, which are the splitting of molecules with electricity. But he himself was not a proponent. -
Marie and Pierre Curie
Marie Curie helped to find a way to get the atomic mass of an atom. She also discovered that the atom was indivisible and unchangeable. -
Henri Becquerel
Found that most atoms are not radioactive. Also neuclei are stable and atoms allow objects to stay the same. -
J.J. Thomson
Discovered the electron. Quoted that the atom is filled with electrons. Created a model also known as the "Plum Pudding Model". -
Max Planck
Used the idea of quanta to explain hot glowing matter. Showed that light must be emitted and absorbed in discrete amounts if it was to correctly describe observed phenomena. -
Albert Einstein
Published the equation E=mc^2. -
Ernest Rutherford
Discovered that the atom was filled with the empty space. Also found that it contained a small nucleus. -
Robert Millikan
Developed the oil-drop experiment. Hypothesized that the mass of a single elect.ron was at least 1000 times smaller than that of the smallest atom -
Neils Bohr
Built a model made up of successive orbital shells of electrons. Developed an explanation of atomic structure that uderlies regularities of the periodic table. -
Wolfgang Pauli
Started with the completion of atomic shells. Added a spin quantum numbers. Two electrons in an atomic structure can never have all four quantum numbers in common. -
Friedrich Hund
Worked on the electronic structure of atoms and molecules. Known for Hund's Rules. -
Werner Heisenberg
Discovered the uncertainty principle and explained ferromangnetism based on the atomic structure. -
James Chadwick
Atoms contain neutral particles called neutrons in their nucleus along with subatomic particles.
