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400 BCE
Democritus
Democritus thought that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. -
340 BCE
Aristotle
Everything in motion is always moved by something else. -
300 BCE
Plato
Plato's theory is that the physical world is not as real or true as timeless, absolute, unchangeable ideas. -
The Alchemists
The Alchemists was a group of scientists in the 16th century. Some of the scientists were Robert Boyle, Lawrence M. Principe, and Paracelsus. -
Period: to
Lavoisier
Lavoisier atomic theory is that matter is not destroyed nor created in chemical reactions. -
Period: to
John Dalton
The first part of John Dalton's atomic theory is that matter is made up of atoms which are invisible. The second part is that all atoms of a given element are the same size and have the same properties. The third part is that compounds are combinations of two or more atoms. -
Newland law of octaves
Newland's law of octaves was founded in 1864 and stated that if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements. -
Period: to
Robert Milikan
Robert's first major find was accurate determination of the charge carried by an electron using the elegant falling-drop method. -
Mendeleev's Periodic table
Mendeleev made his periodic table in 1869, he arranged it so the groups with similar properties fell into a vertical table. -
discovery of radioactivity
Wilhelm Roentgen exposed potassium muranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper, assuming that the uranium absorbs the sun's energy and then emits it as X-rays. -
Discovery of the electron
In the 1880s and the 90s scientist searched cathode rays for carries of the electrical properties then it was discovered by J.J Thomas in 1897. -
Plum pudding model
The Plum pudding model is on of the older models for the atom. -
Planck's quantum theory
This theory is when particles can emit or absorb energy in quantities only. -
Rutherford's gold foil experiment
In his experiment gold foil was hit by alpha particles with a positive charge most of them went through but this shows that gold atoms are mostly empty space. -
Charge of an electron
Robert Milikan discovered the charge of an electron by using negativity charged oil droplets, the charge of an electron is 1.60217663 × 10-19 coulombs. -
Bohr's planetary model
In Bohr's model the electrons travel around the nucleus of the atom in distinct circular orbits. -
Mosely's atomic numbers
Mosely published a paper where he concluded that the atomic number is the positive charges in the nucleus. -
Schrodinger equation
This equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. -
Discovery of the proton
James Chadwick announced in May 1932 that the core also contained a new uncharged particle, which he called the neutron. -
Heisenberg uncertainty principle
This principle states we can not know the exact position or speed of a particle like a proton or electron. -
Discovery of the proton
James Chadwick in May 1932 announced the core also had a new uncharged particle the neutron. -
Photoelectric effect
The photoelectric effect is where a electrical charged particle is released from a material with it absorbs electromagnetic radiation.