Cell and Molecular BiologyThe Atom: Nucleus, Electrons, Isotopes
The nucleus holds almost all of an atom's mass; the electrons hold almost all of its volume. This article works through the three numbers behind that structure — the proton count Z that fixes the element, the mass number A that separates the isotopes, and the mass missing from ¹²C — using CODATA 2022, NIST and IAEA data.
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