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400
Democritus
Democritus was a Greek philosopher, who discovered the atomos (invisible) in 400 B.C. Democritus figured that after dividing a piece of matter so many times, the piece of matter will eventually become indivisible. -
Period: 400 to
Atomic Timeline
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John Dalton
John Dalton is known as the father of modern atomic theory.
5 points in his atomic theory:
1. All matter is made of atoms. Atoms are indivisible and indestructible.
2. All atoms of a given element are identical in mass and propoerties.
3. Compounds are formed by a combination of two or more different kinds of elements.
4. A chemical reaction is a rearrangement of a toms.
5. Atoms can neither be created nor destroyed. -
Henri Becquerel
An experimental attempt gone astray, left Henry Becquerel, a French physicist, a new found discovery - natural radiation. Through flourescing crystals (uranium compound called potassium uranyl sulfate), a photographic plate, and a copper cross, Becquerel discovered that the crystals were emitting natural radiation. -
JJ Thomson
JJ Thomson is the scientist who proposed to plum pudding model, otherwise known as the, Chocolate Chip Cookie or Blueberry Muffin model. Thomson was the first to discover electrons and theorized that the atom was a neutrally charged particle. He assumed the negative and positive charges would cancel out each other, only to later be proven invalid by Rutherford and the gold foil experiment. -
Marie Curie
Marie Curie and her husband, Pierre, unknowingly gave their bodies to science as they watched the bottles of radioactivity glow like "fairy lights," quotes Marie Curie. -
Robert Millikan
Millikan used the Oil Drop experiment to discover the charge of an electron, -1.6x10-19 C. Millikan charged each droplet differently during the experiment, only to find the charge was always a multiple of 1.6x10-19 C. -
Ernest Rutherford
While JJ Thomson was the first to discover the electrons, Ernest Rutherford was the first to discover nucleus in his gold foil experiment. This experiment disproved Thomson's plum pudding model, as well as allow Rutherford to conclude that there is a vast area of empty space around the atom. This means that Thomson was partially correct in his proposition of empty space along with the plum pudding model. -
Neils Bohr
Bohr polished Rutherford's model with the following add ons:
1. Electrons may orbit the nucleus without losing energy
2. Electrons may moveonly in fixed orbits of specific energies
3. Electrons with low energy will orbit closer to the nucleus than electrons with a higher energy
Bohr also proposed that when electrons jump from a ground state to an excited state, it is because the atom is either absorbing or emitting radiation. -
Louis deBroglie
deBroglie discovered the electrons could be similar to light, in a way where electrons could play as both a particle or wave. This unearthing, allowed a specific wavelength, energy, and frequency (Bohr energy levels) to be set up around the nucleus. -
Werner Heisenberg
Soon after deBroglie's discovery, Heisenberg posed a new question to explore. Could you locate the exact location of the electron within the wave? Heisenberg concluded no, because of what he calls the "uncertainty principle."
1. To view an electron in its orbit, you must shine a wavelength of light on it that is smaller than the electron's wavelenght.
2. Short wavelengths of light have high energy.
3. Electrons will absorb that energy.
4. The absorbed energy will change the electron's location -
Erwin Shrodinger
Shrodinger developed functions and equations to help better locate and electron through its orbitals. Orbitals are basically electron, density clouds. You will be more likely to find an electron in a cloud with high density than in one with a lower density. These orbitals tie into the four quantum numbers and orbitals s, p, d, and f block on the periodic table. -
James Chadwick
James Chadwick discovered the neutron, and aided in the splitting of uranium-235. Chadwick soon concluded the building of atomic bombs was possible and even inevitable, motivating President Roosevelt to build the atomic bomb.
