Atomic Mass of Xenon (Xe)
The relative atomic mass of Xenon is 131.29 u — the weighted average of its naturally occurring isotopes, on the carbon-12 scale.
Looking for Xenon's atomic mass without wading through a whole chapter? Here is the direct answer first, then the tables and derivations examiners want to see. Every number on this page comes from the same engine that powers the interactive table. Need the whole picture instead — history, characteristics, uses, exam questions? The full Xenon page is one click away.
Xenon by the numbers
One Xenon atom carries 54 protons in its nucleus; add the neutrons of its commonest isotope (about 77) and you get its mass number, roughly 131.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 54 |
| Relative atomic mass | 131.29 u |
| Protons | 54 |
| Neutrons (commonest isotope) | 77 |
| Electrons | 54 |
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 (131.29). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Xenon a whole number?
No. 131.29 u is the average of Xenon'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 Xenon have?
Neutrons = mass number − atomic number. For Xenon's commonest isotope that is about 131 − 54 = 77, though the exact count differs between isotopes.