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Discovery of the Proton
In 1911 Ernest Rutherford conducted his Gold foil experiment in which he beamed alpha particles through a thin sheet of gold foil. He and his collegues expected the particles to pass through with very little defelction based on their knowledge of the then accepted model of the atom. He was however, surpirsed to see that the alpha particles had very large deflections at extreme angles. He then determined that the previous Plum Pudding atomic model was wrong and decided that the alpha particles bouncing off were hitting positively charged dense centers (alpha particles have positive chrage and so do the centers therefore they repel each other). He discovered the nucleus of an atom and he was able to deduce that because an atom was self contained and negatively charged particles orbited around the nucleus (a.k.a. recently discovered electrons), the nucleues must have subatomic particles within it to attract the electrons and keep the atom together. The positively charged particles in the nucleus of the atom were called protons.
It is not clear cut who exactly discovered the Proton because the process was gradual and consisted of a series of theoretical assumptions, and experiments based off of those realizations. However many attribute the majority of the discovery of this subatomic particle to ernest Rutherford, though the conept came from an experiment created by Eugen Goldstein.
Sir Ernest Rutherford in his “prime“
The first step towards the dircovery of Protons occred when Eugen Goldstein conducted his canal ray experiment. He discovered in 1886 that in addition to the negativeley charged subatomic particles, atoms had positive charges. He proved this by setting up a Cathode Ray tube similar to the one in the experiment conducted by JJ Tomphson that we discussed in class. He then filled the tube with hydrogen and expected the particles to flow from the negatively charged cathode to the positively charged annode. However, he saw that his tube also emitted a glow on the cathode end. He deduced the only way for particles to flow towards the negativly charged cathode was if those particles were positively charged. Goldstein was able to prove the existence of positively charged subatomic particles.
Protons carry an equal, but opposite, charge to electrons, but protons are much larger and heavier than electrons.
Rutherford also conducted a second experiment that was closely realted to the discovery of Protons. This time he filled a chamber wiht Nitrogen gas and he shot alpha particles through that gas. He observed that thealpha particles actually entered the nitrogen nucleus and ejected a poitively charged subatomic particle (a.k.a. proton).
This is a great Video explaining a little but about the gold foil experiment we talked about in class and also showing why the nucleus discovered by Rutherford had to be positivly charged. The fact the the nucleus was positively charged proved the existence of a positively charged subatomic particles beacuse that would have been the only possible source for the charge.