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Chemistry
Isotopes and average atomic mass
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Add or remove neutrons to make isotopes and read the mass number, mass, stability and abundance; then mix isotopes in the test chamber to see that the average atomic mass is a weighted average.
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Model notes
- Isotopic masses, abundances and standard atomic masses are the source model's data (an older NIST table, e.g. H 1.00794 and Li 6.941), which differ from the current CIAAW values used by the Periodic table resource. The "Compare with CIAAW" section shows today's values for comparison; it does not replace the model's numbers.
- The average atomic mass in the chamber is the sum of the isotopic masses (amu) of its atoms divided by the number of atoms: a weighted average. Exercises often approximate with mass numbers (Cl: 35 × 0.7576 + 37 × 0.2424 ≈ 35.48); the model uses isotopic masses (Cl ≈ 35.45).
- Nature's mix is an illustrative sample of about 1,000 atoms: each isotope gets 1,000 × its abundance, rounded, and at least one atom. The sample's shares and average can therefore differ from the abundances and the reference value; the atom counts are not real amounts.
- "Unstable" means the nucleus is not in the model's list of stable isotopes; the jiggling nucleus is only a sign, the model does not simulate decay or half-life. Mixtures use stable isotopes only.
- Particles and distances are not to scale; the electron cloud is a simplified drawing. Atom positions in the chamber are random and do not affect any number.