question 1

Examine the history of the development of the atom. We have already discussed themajor players in the development of the atom. Pick out at least 8 major players whohelped aid in the development of the concept of the atom. Then explain eachexperiment in a concise explanation. Then explain how each one aided in thedevelopment of the next or how their concept assisted in the further development of the current quantum model of the atom.



In 1803, John Dalton developed his Atomic Theory. According to Atomic Theory, matter is made up of indivisible atoms, all atoms of an element are identical, atoms are not created or destroyed, atoms of different elements have different weights and chemical properties, and atoms of different elements combine to form compounds. Dalton's theory had flaws, but it helped proceeding scientists understand atoms.


In 1830, Michael Faraday did an experiment that showed evidence of electrons through glowing in a magnetic field caused by electrical charges. Though electrons were not known of at the time, this experiment showed that something electrically charged existed.


In 1897, J.J. Thompson theorized that everything in the universe was made of small particles. He found that cathode rays could be deflected by an electric field, and that the rays were really particles. He also formed the Plum Pudding model of the atom, which showed electrons floating freely within the nucleus. Thompson concluded that there must also be positively charged particles, disproving the section of Dalton's theory that stated atoms were indivisible.



In 1911 Ernst Rutherford revised Thompson's atomic model in studies of the deflection of alpha particles as they were targeted at thin gold foil sheets. Most of the alpha particles penetrated straight through the sheets, but a few were deflected at small angles. This meant that the positive charge and mass of an atom were located in the center of the atom and only made up a little bit of the total volume. This center was named the nucleus.


In 1917, Thompsons theory that the atom was split in to smaller particles was further reasearched by Robert Millikan. By experimenting with an "oil-drop apparatus" that measured electron charge. He proved that the mass of electrons was 1000 times smaller that atoms.



In 1913, A. van Broek proposed that instead of being compared to the atomic weight, the postivive atomic charge should be equal to the atomic number, as is thought today.



In 1914, a scientist named H.G.J. Mosely formed a hypothesis that the nucleus emitting x-rays effected the rays frequencies. Through this hypothesis, he inferred that the positive charge in atoms was equal to the atomic number.



In 1932, James Chadwick proved the existence of particles in the atom that were not electronically or positively charged. These are called neutrons.