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Period: 300 to
Developement of the Atomic Theory
Includes scientists whose ideas and discoveries lead towards the current Atomic Theory. -
400
Aristotle
Aristotle began the principle of continuum, proposing the idea that regardless of the how many times matter is cut in half, there is always a remaining, smaller piece of matter. He focused on the break-down of the four elements of air, earth, water, and fire. -
405
Egypt Overthrows Persian Rule
Egypt becomes one of the world's greatest ancient civilizations. -
410
Democritus
Democritus created the idea an ultimate particle existed, he called the particle "atomos". -
Invention of the Lightening Rod
Benjamin Franklin "flies a kite" and discovers that lightening can be conducted through metal. -
Joseph Proust
Proust created the Law of Constant Composition, which states that the composition of a substance is always the same, regardless of how the substance was made or where the substance is found. -
End of the French Revolution
Nepoleon becomes the ruler of France. -
John Dalton
Dalton experiemented with the weight ratios of elements in order to create the Law of Simple Multiple Proportions, explaining: elements are made up of paritcles cal atoms, atoms cannot be created ordestroyed, in a pure element, all atoms have identical masses, elements are seperated by the weight of their atoms, atoms of different elements create a compound, and a chemical change occurs when the bonds of atoms are rearranged. -
Expedition of Lewis and Clark
The exploration Louisiana Territory. -
The first running passenger railroad invented
The United States begins transportaion for the public between Baltimore and Elliott's Mills, Md. -
J.J Thomson
Experiementing with the cathode ray tube ( a tube in which electric currents pass through a gass at a low pressure), Thomson created the Raisin Pudding Model, showing that matter is electrically neutral and electrons are lighter than atoms. The model showed the negatively charged electrons surounded by positive "space". He also compared an atom's charge to its mass: e/m = -1.76 x 108 coulombs/g. -
Max Planck
Planck is known for his work in producing the quantum theory. Relating the energy in one quantum (photon) of electromagnetic radiation to the frequency of that radiation, Planck created the number called Planck's constant (h =6.626068 × 10-34 m2 kg / s), which is used in the equation E = h X f, where E = energy of light and F = frequency. -
U.S. President McKinley is assassinated
McKinley is shot near Niagra Falls and killed. -
Henri Becquerel
Beecquerel disvoered radioactivity, or the decay of a nucleus by the breaking off of a nuetron or protron. Using sunlight through photographic plates to stimulate the growth of crystals, Becquerel discovered x-rays being emited off uranium. -
Ernest Rutherford
Rutherford contributed the idea that an atom is made of a positively charged nucleus surrounded by orbitting, negatively charged electrons. Rutherford discovered that the nuclues held the positive charge and mass of an atom, and it only made up a small fraction of the total volume. when he conducted an experiment where radioactive particles were fired through metal foil, resulting in the majority of the particles passing through the metal with only a reflecting off of the foil, -
Robert Millikan
Millikan determined the unit charge of the electron (e = 1.60 x 10-19 coulombs). -
Invention of the oreo cookies
Nabisco produces the first oreo cookie. -
Neils Bohr
Using Rutherford's atomic structure model, Bohr discovered that while orbiting the nucleus of an atom, an electron may gain energy (known as an "excited" electron), from light or heat, and move up energy levels. When the electron loses its excess energy it declines back to its groundstate. This transfer from different energy levels emits a light that is different for all elements. -
First Olympic Winter Games
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Werner Heisenberg
Werner contributed to the theory of quantum mechanics, concerning the subject of the radiation emitted from an atom. Heisenberg thought that position and velocity should be shown by matrices instead of numbers. In his principle of uncertainty, Werner stated that in determing the momentum and position of an orbiting particle, the errors in the calculation will be greater than the value of "h", or the quantum number, -
Erwin Schrodinger
With the Principle of Uncertainty, Schrodinger suggested that electrons move in waves (an electron's momentum), and it is impossible to determine their exact location within an orbit (an electron's position). This means that an energy level has sublevels, which are made up of orbits. -
Louis de Broglie
Broglie discovered the "wave nature" of electrons. He foudn that a wavelengthcan be calculated by h/p, where "p" is the momentum of the electron and "h" is Planck’s constant. -
James Chadwick
Chadwick proved that neutrons exist; they are located in the nuclues and make up about half the mass of an atom. He concluded that: the number of protons is equal to the atomic number "Z", a neutral atom means that the number of electrons is equal to the number of protons, the mass number "M" is equal to the sum of the number of
protons and neutrons, and the number of neutrons is equal to the difference between the mass and atomic number. -
Adolf Hitler Becomes Chancellor of Germany
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First Credit Card Introduced and Used
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Soviets launch the first man into outer-space
Yuri Gagarin, was the first man to reach space and the first to orbit the world. -
Elvis Presley dies
