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100
Democritus Introduces the Atom!
This model showed us what you get when you get something so small it can't be divided any further. It provided a basic explanation of the basic unit of matter. This man was a philosopher & therefore did no experimentation. -
100
Aristotle presents his theory!
Aristotle explained in an easily understandable way that all objects must be made up of one of 4 things: Air, Fire, Earth, or Water. (i.e. if it's wet it's made of water). No experimentation was done as Aristotle was a philosopher & philosophers don't work w/ their hands. -
John Dalton's Atomic Theory Etc!
John Dalton presented his atomic theory which generally said elements are made of microscopic atoms ; atoms which can't be created or destroyed, but can be combined/seperated from compounds. He also came up with the Law of Multiple Proportions. He experimented with such things as water, ammonia, & hydrogen. -
Henri Becquerel discovers radioactivity!
This man performed experiments with a photographic plate & 2 pieces of paper, adding a couple of extra items towards the end. He discovered there was a phosphorescent substance giving off rays of some sort. On a side note, he discovered the element thorium. -
Marie Curie makes new discoveries!
Marie & her husband Pierre Curie both worked in a shack of a lab, doing extensive experiments with Uranium. Marie discovered the radioactivity of Uranium, & disproved the misconception that atoms are indivisible. She & her husband also discovered 2 new elements: Polonium & Radium. -
J.J. Thomson Discovers Electrons!
Thomson experimented with cathode rays, which led to the discovery that electrons have a negative charge to them. He also discovered isotopes & invented the mass spectrometer, which measures the mass-to-charge ratio of elements. -
Robert Millikan Finds Mass of Electrons!
Robert Millikan discovers/figures out the charge of electrons. He explained with his equations, the charge of electrons. He used the classic oil drop experiment. Very efficient. -
Niels Bohr Proposes A Totally New Atomic Model
Niels Bohr proposed a completely new idea for the atomic model in 1913. He looked at Rutherford's model, & with much reasoning & many math equations, disproved Rutherford's theory. Bohr said electrons fly around the nucleus & can change their energy in certain steps. -
Ernest Rutherford's Ideas!
Ernest Rutherford made many discoveries with the Gold Foil experiment. He was also the first scientist to transform a nitrogen atom into an oxygen atom. This man showed it is possible to transform atoms into other atoms. -
James Chadwick & The Neutron!
In 1932, (Sir) James Chadwick discovered the neutron. Interestingly enough, he was experimenting with making ions when he came across this discovery. This was important in leading upto the creation of Uranium 235! -
In Other News: Manhattan Project!
The Manhattan Project was a huge war project meant to build a war-winning atomic bomb. Perhaps the most important component was uranium-235, a rare isotope of uranium. Despite difficulty, these scientists had to seperate certain parts of the abundant uranium-238 to transform it into the potent isotope required. -
The Quantum Model!
With contributions from 15 - 20 scientists, the Quantum Model tells us we can't know the exact position/momentum of electrons all at once. Since electrons do move fast however, this model uses an electron cloud which predicts where an electron should be.
