![]() ![]() Star-forming nebulae filled with hydrogen gas in deep space are often referred to as H-II regions. Given that hydrogen is by far the most common element (or molecule) in the universe, and since hydrogen nuclei are just single protons, then suffice it to say the science of protons can teach us much about the distribution of matter and the violent mechanisms that drive some of the most energetic phenomena in the cosmos. (Image credit: NASA, ESA, CSA, Data reduction and analysis : PDRs4All ERS Team graphical processing S. The Orion nebula is an H-II region filled with hydrogen gas. The Orion Nebula captured in unprecedented detail in this image by the James Webb Space Telescope. Robert Hofstadter, who was an American physicist who won the Nobel Prize for his work characterizing protons and neutrons, described this scale of 10^–15 meters as a 'femtometer', named after the famous physicist Enrico Fermi. ![]() Given that protons are subatomic particles at the very heart of an atom, they are therefore extremely small, measuring just hundreds of trillionths of a meter (10^–15 meters). Remove an electron from around an atom, however, and this upsets the balance between the cumulative charges of the electrons and the protons, and the atom becomes positively charged - an ion. Because their charges are equal, and because the other co-inhabitant of the atomic nucleus, the neutron, is neutral, then so long as the number of protons and electrons are equal then their charges cancel out and atoms are electrically neutral. This is the exact equal and opposite of the charge of an electron, which is - 1.602192 x 10^-19 coulombs. The elementary charge of the proton is 1.602192 x 10^–19 coulombs (C). Only quarks have a smaller charge, being a third or two-thirds of the elementary charge. ![]() It is the basic unit of charge against which all other charges are measured. What is the charge of a proton?Ī proton has what is called an " elementary charge ", or "e" in shorthand. Today we know that protons (and neutrons) are formed from even smaller particles, quarks, and that the nucleus of an atom is made from protons and neutrons (with the exception of the basic form of hydrogen, which has no neutrons). He called the hydrogen nucleus a proton, meaning "first" in Greek because Rutherford saw it as the first building block for all atoms. Various experiments, including some performed by Rutherford, showed that hydrogen nuclei could come out of other elements, and by 1920 Rutherford had figured that hydrogen nuclei must be the basic building block of all atomic nuclei since hydrogen is the lightest element. In the gold leaf experiment, the deflected alpha particles were encountering this nucleus. This model, albeit simplified because it doesn't incorporate the quantum mechanical behavior of the electrons, is referred to as the Bohr model after Niels Bohr, who along with Rutherford put all the pieces together. This convinced Rutherford that atoms actually consisted of a tiny, tight nucleus surrounded by empty space with electrons orbiting around the nucleus at a distance. That could only happen if there were a knot of electric charge at the center of an atom, rather than being spread out as in the plum pudding model. Instead, Geiger and Marsden found in their experiment that sometimes the alpha particles were deflected at large angles, or even bounced straight back. (Image credit: Science & Society Picture Library via Getty Images) Photograph of Ernest Rutherford and Hans Geiger with their alpha particle counting apparatus. ![]()
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