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I'm suppose to write out reactions where atoms send out alpha radiation and decay. The book uses the 4-2 H, 4 as nucleon number and 2 as proton number, but isn't that wrong? The mass of helium is greater than the alpha particle due to two electrons? Shouldn't they use a different notation for the alpha-particle other than that for helium?

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Hint: The book likely doesn't care about the (relative) error it is making. Why? –  Qmechanic May 20 '12 at 11:19
    
I get that it's a very small error to make. I thought accuracy was a good thing :( –  Algific May 20 '12 at 11:47
    
I think the notation you wrote in your question is not what you intended. Apart from that, the difference is small and an alpha particle is a fully ionized helium atom so using the helium notation is not out of the question. In my classwork, I seem to remember people simply using a lowercase alpha as the symbol. –  AdamRedwine May 20 '12 at 15:31
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Alpha particles are essentially the same as a deionized Helium atom. The mass of the electron pair can be neglected because the mass of an electron is significantly smaller than that of the protons and the neutrons in the nucleus, so don't have much of an effect for simple purposes. See http://en.wikipedia.org/wiki/Proton-to-electron_mass_ratio which shows the scale of the difference.

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I do believe the binding energy of the electrons in helium is greater than the rest mass of two electrons. Either way, you are correct that it makes little difference. –  AdamRedwine May 20 '12 at 15:28
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