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440
Plato
Plato believed that earth, air, fire and water were four of the elements, but he also argued that there must be a fifth based off of the five shapes (mathematical). He postulated that the fifth elemnt was "ether", or the heavens. -
440
Empedocles and Aristotle
Both Greeks believed that earth, air, fire, and water were the only four elements. According to their theories, every time you cut a piece of matter, it would get smaller. -
460
Leucippus and Democritus
The founding fathers of atomic theory, Leucippus and Democritus discovered that there were various basic elements that made up matter. They are aslo credited for the discovery of the atom and the fact that matter is composed of small atoms moving in a void. -
Britain became a country
Britain became a country in 1707. -
Formation of America
The U.S. became an official country. -
Haitian Revolution
The revolution in which Haitian slaves were victourious in their fight to end slavery. -
John Dalton
Proceeding experiments with different gases, Dalton came up with an atomic theory that suggests (1) Matter is made up of atoms that are indivisible and indestructable, (2) all atoms of an elemnt are identical, (3) atoms of different elements have different weights and different chemical properties, (4) atoms of different elements combine in simple whole numbers to form protons, and (5) attoms cannot be created or destroyed; when a compound decomposes, the atoms recover unchanged. -
Huang He River Flood
This Chinese flood (also called the Yellow River) killed 900,000 people. -
J.J. Thomson
Thomson discovered electrons through experiments on cathode rays. He realized that the rays consisted of small, negatively charged particles with a mass smaller than a hydrogen atom. -
Max Planck
Planck created the Quantum Theory. He believed that energy was directly proportional to frequency, and created an equation (E = hv) that describes the blackbody spectrum. -
Ernest Rutherford
After the "gold foil experiment" performed by two of his students, Rutherford postulated the nuclear structure of an atom. He also created laws of radioactive decay, identified alpha particles as helium nuclei, and discovered alpha and beta rays. -
Millikan
Using an oil drop experiment, Millikan was able to determine the unit charge of an electron. -
Niels Bohr
Niels Bohr created a successful quantum model of the atom in 1913. He was the first to discover that electrons travel in separate orbits around the nucleus, as well as the fact that the number of electrons in the outer orbital determines properites of the element. -
World War I
A global war centered in Europe that lasted until 1918. -
Louis de Broglie
In 1926, Broglie proposed the dualty principle, which states that all partifcles have wave-like properties. This is seen in the equation λ = h/mv, where λ is the wavelength, h is Planck's constant, m is mass and v is velocity. -
Erwin Schrodinger
Schrodinger was responsible for inventing wave mechanics in 1926. His model was an independent form of quantum mechanics, describing that the electron could be found in a given region of space at a given time. -
James Chadwick
James Chadwick discovered the neutron by using scattering data to calculate neutral particles.
