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Democritus-Anciet Greece
DISCLAIMER: Not actually in the year 1800. The ancient greek philosopher Democritus proposed that matter could be divided smaller and smaller until a point where it could not be divided any more. He called matter at this point 'atomos' which translates to 'not to be cut'. In his mind, atoms were small and hard, made up of the same material, and varied greatly in size and shape. -
John Dalton's Atomic Theory
In 1804, John Dalton added on to Democritus' atomic theory. Unlike Democritus, his additions were based on experimentation, not just thought alone. Dalton's theory was based off the fact that different elements had different masses. He theorized that all atoms of an element have the same mass and properties, as well as that atoms could not be created or destroyed. He also thought of the concept that chemical reactions are actually a rearrangement of atoms. -
J.J Thomsons Plum Pudding
The major discovery which Thomson made was the existence of the electron. He found this through experimentation using cathode ray tubes. He tested the tubes for mass, as well as experimented with magnets, and found that the inside of the cathode rays were almot 1000 times lighter than any hydrogen atom. He concluded that there was al ight, negatively charged particle which were a building block for all atoms. From this he created his atomic model, a positive sphere filled with tiny negative bits -
Albert Einstein and Light
Einstein had two major contributions to this theory. His first contribution had to do with the discovery of photons. Because the way light travels, he theorized it must travel in bundles which he called photons. The more important contribution is the wave-particle duality of an electron. Through the double slit experiment, he discovered that depending on the circumstance, an electron can behave as both a wave and a particle. -
Robert Millikan's Oil Drop Experiment
Millikan's impact to the atomic theory was the discovery of the exact charge of a single electron. He found out this charge through measurments related to his Oild Drop Experiment. This experiment involved a mist of oil being sprayed into a vacuumed chamber. The time it took to reach their terminal velocity was measured, and then a uniform electric field was created using plates at the bottom of the chamber. The time was then measured again and the differences were recorded. -
Rutherfords Atomic Theory
Rutherfords major contribution to the atomic theory was the discovery that atoms are mostly comprised of empty space. He discovered this fact through his gold foil experiment. His original concept was that he would shoot alpha particles at a thin sheet of gold foil, and they would be reflected back. What actually happened is that most of the particles moved through the foil. From this he theorized that the atom was actually a positive mass in the centre, surrounded by negative electrons. -
Niels Bohr's Atomic Theory
Bohr's impact to the atomic structure was the introduction of orbital electrons. He was familiar with Rutherford and his gold foil experiment, but he was also familiar with Max Plancks work in quatum theories. He theorized that electrons are not just surrounding the nucleus, but orbting it, in different energy levels, or rings. He also introduced the concept of electrons dropping to a lower enegry level and releasing quantum energy. -
Henry Moseley and The Periodic Table
Moseley had less of an impact to the atomic theory, and more of an impact to the periodic table. He was one of the major people who placed new elements that were discovereded. He developed a more precise way of placing elements onto the table, not just dependent on mass, but on the X-Ray spectra of the element. He filled in major gaps which previously existed and helped complete the table to what we know it as today. -
Erwin Schrodinger's Standing Wave
Schrondinger's contribution has to do with the wave properties an electron presents. He theorized that the electron would act like a wave going from the nucleus, to the postion on the orbital shell the electron exists at. He found that if he used that imagery, the electron would be as it if were a standing wave, meaning it appears stationary even though it is constantly moving. -
Heisenberg Uncertainty Principle
Heisenberg's addition to the atomic theory was his Uncertainty Principle. He created this principle after his work with the atom and electrons. The principle states that the more precisely one is to know the position of an election, the less precisely they can know the momentum, and vice-versa. This principle was discovered when the speed of the electron was attempted to be measured, but once measured, the location could not be determined accurately, hence the Uncertainty Principle. -
James Chadwicks Neutron
Chadwicks addition to the atomic structure was the discovery of the neutron. Prior to this discovery, it was believed that there were twice as many protons as electrons in any given atom, to compensate for the lost mass. Through gold foil like experiments and mass spectoronomy, he had found there seemed to be something missing in the atom. He, as well as Rutherford, hypothesized a neutral particle, the size of a proton, which exists in the nucleus of the atom.
