Atomic Mass of Cerium (Ce)
The relative atomic mass of Cerium is 140.12 u — the weighted average of its naturally occurring isotopes, on the carbon-12 scale.
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Cerium by the numbers
One Cerium atom carries 58 protons in its nucleus; add the neutrons of its commonest isotope (about 82) and you get its mass number, roughly 140.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 58 |
| Relative atomic mass | 140.12 u |
| Protons | 58 |
| Neutrons (commonest isotope) | 82 |
| Electrons | 58 |
Atomic mass vs mass number
Mass number (A) counts particles — protons + neutrons in one specific atom, always a whole number. Relative atomic mass is the experimentally measured average over all natural isotopes, so it comes out fractional (140.12). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Cerium a whole number?
No. 140.12 u is the average of Cerium's natural isotopes, which is why it lands between whole numbers. The mass number of a single isotope, though, is always whole.
How many neutrons does Cerium have?
Neutrons = mass number − atomic number. For Cerium's commonest isotope that is about 140 − 58 = 82, though the exact count differs between isotopes.