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Aristotle
Century: 2000 years in BC
He developed a theory that was based on the 4 elements.
Aristotle’s theory made a great generalization off all matter being made of the four elements: fire, water, earth, and air.He also said there were four qualities to these elements: dryness, hotness, coldness, and moisture. -
Henri Becquerel
Century: 1896
He thought phosphorescence was related to x-rays, a newly discovered form of radiation.
To test his idea that phosphorescence was related to x-rays, he sealed a photographic plate in black paper to prevent it from being exposed to visible light. -
James Chadwick
Century: 1932
He discovered the nuetron, and found that it was slightly heavier than the proton.
He also said the center nucleus consisted of protons and nuetrons, containing almost all the mass of the atom. -
Marie & Pierre Curie
Century: 19th Pierre and Marie Curie are best known for their pioneering work in the study of radioactivity, which led to their discovery of the elements radium and polonium. -
Robert Millikan
Century: 1909 He came up with the calculation of the mass of the electron and the positively charged atoms. e = 1.60 x 10-19 coulombs -
John Dalton
Century: He said that all matter is made of atoms. Atoms are indivisible and indestructible.
He also said that all atoms of a given element are identical in mass and properties. -
Democritus
Century: 1800's
Democritus atomic model is made up with a sphere that cannot be seen or invisible. The sphere has no nucleus or electrons. They differ in shape, size and temperature.
He said atoms can't be destroyed. -
Erwin Schrodinger
Century: Edwin Schrodinger stated that rather than electrons being distributed within an electron configuration of shells and energy levels, they were arranged in orbitals which were systematically distributed within Electron Clouds.
He defined orbit as the region of space that surrounds a nucleus in which two electrons may randomly move. -
Ernest Rutherford
Century: 1911 He proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. -
J.J. Thomson
Century: 1897 He deduced that the electron was a component of all matter and calculated the charge to mass ratio for the electron.
e/m = -1.76 x 108 coulombs/g -
Max Planck
Century: He came up with the quantum theory.
This theory revolutionized our understanding of atomic and subatomic processes, just as Albert Einstein's theory of relativity revolutionized our understanding of space and time. -
Werner Heisenberg
Century: 1925 He came up with the Matrix mechanics which was the first conceptually autonomous and logically consistent formulation of quantum mechanics. It extended the Bohr Model by describing how the quantum jumps occur. -
Antoine Lavoisier
Century: 1800's He created the first version of the law of c. This principle is now called the law of conservation of mass. -
Henry Mosely
Century: 1913 He discovered that the energy of x-rays emitted by the elements increased in a linear fashion with each successive element in the periodic table. He proposed that the relationship was a function of the positive charge on the nucleus. This rearranged the periodic table by using the atomic number instead of atomic mass to represent the progression of the elements. -
Niels Bohr
Century: 1913
He said that the atom was a positiviley charged nucleus surrounded by electrons that traveled in circular orbit, just like the solar system.
