The nucleus - number of protons. Any nucleus can be written...

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The nucleus When we looked at the atom from the point of view of quantum mechanics, we treated the nucleus as a positive point charge and focused on what the electrons were doing. In many cases, such as in chemical reactions, that's all that matters; in other cases, such as radioactivity, or for nuclear reactions, what happens in the nucleus is critical, and the electrons can be ignored. A nucleus consists of a bunch of protons and neutrons; these are known as nucleons. Each nucleus can be characterized by two numbers: A, the atomic mass number, which is the total number of nucleons; and Z, the atomic number, representing the
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Unformatted text preview: number of protons. Any nucleus can be written in a form like this: where Al is the element (aluminum in this case), the 27 is the atomic mass number (the number of neutrons plus the number of protons), and the 13 is Z, the atomic number, the number of protons. How big is a nucleus? We know that atoms are a few angstroms, but most of the atom is empty space. The nucleus is much smaller than the atom, and is typically a few femtometers. The nucleus can be thought of as a bunch of balls (the protons and neutrons) packed into a sphere, with the radius of the sphere being approximately:...
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