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sorry that this is an easy question but I am just a bit confused about nuclide notation. When you say e.g. $^{240}_{94}\text{Pu}$, are you referring to the atom of $\text{Pu}$ or only its nucleus?

It doesn't make this clear in my revision guide so I wanted to make sure.

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Either.

It's context dependent. Chemists generally mean the whole atoms, nuclear physicists usually mean the nucleus, and people not in those categories could mean either. And there are exception to all those rules or thumb.

And the distinctions is important when people start throwing masses around because the mass of an electron is almost on the same order as typical per-nucleon mass deficits.

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    $\begingroup$ I would add that chemists are usually talking about the natural isotope mixture when they are talking about elements, which is very important for stoichiometry of chemical reactions (1 mol of different isotopes and mixtures has different mass/weight!) and mass spectroscopy. $\endgroup$
    – CuriousOne
    May 11 '15 at 0:51
  • $\begingroup$ As another specific example, the masses (or rather, mass excesses) tabulated in the nuclear wallet cards are for neutral atoms. $\endgroup$
    – rob
    May 11 '15 at 11:27
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The notation is that of one specific isotope (isotopes are nuclides with the same number of protons) of the chemical element Pu. 94 is the number of its protons, which is also the total charge, 240 is the total number of nucleons (protons and neutrons). In a neutral Pu atom there will always be 94 electrons to offset the charge of the protons in the nucleus. All neutral Pu atoms therefor have the same number of protons and electrons, but the number of neutrons differs from isotope to isotope. When chemists are talking about an element, they usually mean a chemical mixture of different isotopes of that element, mostly the mixture that occurs naturally.

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The entire atom is referred to by Pu.

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  • $\begingroup$ Thanks, so $^{240}_{94}\text{Pu}$ isn't referring to the whole atom right? Only $\text{Pu}$ is? $\endgroup$
    – user45220
    May 11 '15 at 0:41
  • $\begingroup$ $^{240}_{94}\text{Pu}$ refers to the entire atom as well. $\endgroup$
    – Jimmy360
    May 11 '15 at 0:42
  • $\begingroup$ Wait, so the question in my book is wrong. "Calculate the specific charge of $^{240}_{94}\text{Pu}$." The solution given at the back calculates the specific charge of the nucleus, not the whole atom. $\endgroup$
    – user45220
    May 11 '15 at 0:43
  • $\begingroup$ @user45220 It depends on context. You can talk about an atom of $^{240}_{94}\text{Pu}$ or a nucleus of Pu. $\endgroup$
    – Jimmy360
    May 11 '15 at 0:47
  • $\begingroup$ @user45220 If no information is given expect $^{240}_{94}\text{Pu}$ then you should assume either a neutral atom or a nucleus, but since it asked for charge, it is referring to a nucleus. $\endgroup$
    – Jimmy360
    May 11 '15 at 0:49

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