Events
1785 - Law of conservation of mass by LaVoisier.1803 - Dalton's atomic theory.1897 - JJ Thomson discovers the electron
using modified cathode rays.1904 - Hantuaro Nagoka represents the atom as a large,
positively charged sphere with rings of negative electrons.1911 - Ernest Rutherford designs an experiment to test the existing atomic model.
He hypothesized that an atom has a positive nucleus surrounded by negative electrons.1913 - Neils Bohr theorized electrons within an atom posses
only certain discrete energies called energy levels.1914 - Rutherford coined the word proton for the
smallest unit of positive energy.1932 - James Chadwick demonstrates that an atomic nuclei
must contain heavy neutral particles and positive particles
through his experiment.1797 - The law of constant
composition by Joseph Proust.1900 - Max Planck suggests that radiation is quantized (it comes in discrete amounts).1909 - Millikan measures the charge of the electron in his famous oil-drop experiment.1923 - Louis de Broglie predicts the wave nature of
electrons and suggested that all matter have wave properties.1925 - The Schrodinger equation: to find the allowed
energy levels of quantum mechanical systems.1927 - Heisenberg Uncertainty Principle: the position and the velocity
of an object cannot both be measured exactly at the same time.Periods
460-370 BC? - Democritus proposed
the idea of an atom and an atomic
theory. He named the invisible
particles atoms.
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