Atomic Mass of Bismuth (Bi)
The relative atomic mass of Bismuth is 208.98 u — the weighted average of its naturally occurring isotopes, on the carbon-12 scale.
Teachers call it "one fact, fully handled" — exactly what this page does for Bismuth. The answer sits at the top in bold; scroll for the working, the shell-by-shell breakdown and the two questions students ask most. Need the whole picture instead — history, characteristics, uses, exam questions? The full Bismuth page is one click away.
Bismuth by the numbers
Z = 83 fixes the protons; the neutron count can vary between isotopes, which is why the atomic mass is an average (208.98 u) rather than a round number.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 83 |
| Relative atomic mass | 208.98 u |
| Protons | 83 |
| Neutrons (commonest isotope) | 126 |
| Electrons | 83 |
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 (208.98). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Bismuth a whole number?
No. 208.98 u is the average of Bismuth'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 Bismuth have?
Neutrons = mass number − atomic number. For Bismuth's commonest isotope that is about 209 − 83 = 126, though the exact count differs between isotopes.