Atomic Mass of Praseodymium (Pr)
The relative atomic mass of Praseodymium is 140.91 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 Praseodymium. 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 Praseodymium page is one click away.
Praseodymium by the numbers
Z = 59 fixes the protons; the neutron count can vary between isotopes, which is why the atomic mass is an average (140.91 u) rather than a round number.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 59 |
| Relative atomic mass | 140.91 u |
| Protons | 59 |
| Neutrons (commonest isotope) | 82 |
| Electrons | 59 |
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 (140.91). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Praseodymium a whole number?
No. 140.91 u is the average of Praseodymium'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 Praseodymium have?
Neutrons = mass number − atomic number. For Praseodymium's commonest isotope that is about 141 − 59 = 82, though the exact count differs between isotopes.