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427 BCE
What Plato Knew About Atoms
Plato introduced the atomic theory, according to which atoms broke down mathematically into triangles, such that the form elements had the following shapes, either fire, air, water, or earth. -
400 BCE
What Did Democritus Discover About Atoms
Democritus believed that atoms were hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until they were stopped. -
332 BCE
What Aristotle Knew About Atoms
Aristotle did not believe in the atomic theory. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed that everything was made of small amounts of these four elements of matter. -
What Lavoiser Discovered About Atoms
Lavoiser worked on defining the laws of conservation of mass. The theory defined that matter was composed of atoms that were not created or destroyed during chemical reactions. -
What John Dalton Discovered About Atoms
Dalton based his theory on the law of conservation of mass and the law of constant composition. The first part of his theory states that all matter is made of atoms. The second part of the theory says all atoms of a given element are identical in mass and properties. -
Newlands's Law of Octaves
Newland's Law of Octaves says that when Elements are arranged in increasing order of Atomic Mass, that the properties of every eighth Element starting from any Element repeat the properties of the starting Element. -
Mendeleev's Pd. Table
Mendeleev found out that when all the known chemical elements were arranged in order of increasing atomic weight. The resulting table displayed a recurring pattern of properties within groups of elements. -
Photoelectric Effect
The photoelectric effect was discovered by a German physicist named Heinrich Rudolf Hertz. In connection with work on radio waves, Hertz observed that, when ultraviolet light shines on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking takes place. -
Discovery of Radioactivity
Henri Becquerel accidentally discovered radioactivity shortly after x-rays were invented. He exposed uranium to light. -
Discovery of the electron
Discovered by J. J. Thomson by experimenting with a cathode ray tube. He demonstrated that cathode rays were negatively charged. -
Plum Pudding Model
An idea proposed by J. J. Thompson, it tried to explain the two properties of atoms known at the time. That being the negative electrons surrounded by the positive protons. They did not know about the nucleus yet. -
Planck's Quantum Theory About Light
Planck's quantum theory determined that different atoms and molecules can emit or absorb energy in discrete quantities only, I.E emit different amounts of light. -
The Charge of an Electron
Robert Millikan determined that electrons have charges through the, Millikan Oil Drop Test. Millikan measured the charge of an electron using negatively charged oil droplets. -
What Did Robert Millikan Discover About the Atom
He discovered an accurate way to determine the charge of an electron. -
Rutherford's Gold Foil Experiment
An experiment where a piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. This showed that the gold atoms were mostly empty space. -
Bohr's Planetary Model
According to Bohr, electrons encircle the nucleus of the atom in a specific way called an orbit. -
Discovery of the proton
A man named Ernest Rutherford is responsible for the discovery of the proton. -
Mosley's Atomic Numbers
He published a paper that concluded that the atomic number was the number of positive charges in an atom's nucleus. -
Shrodinger's Equation
Schrödinger formed a wave equation that calculated the energy in electrons. -
Heisenberg
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Heisenberg Uncertainty Principle
German physicist Werner Heisenberg in 1927 created a principle that states we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy, -
Discovery of the neutron
James Chadwick fired alpha radiation at beryllium sheet from a polonium source. This led to the production of an uncharged, penetrating radiation. This radiation was made incident on paraffin wax, a hydrocarbon having a relatively high hydrogen content.
