Atomic Mass of Potassium (K)
The relative atomic mass of Potassium is 39.098 u — the weighted average of its naturally occurring isotopes, on the carbon-12 scale.
This is the fast lane: one page, one fact, zero digressions. Read the quick answer, check the table, and if your exam needs the full derivation, the sections below walk through it step by step — in Bangla and English, like every page here. Need the whole picture instead — history, characteristics, uses, exam questions? The full Potassium page is one click away.
Potassium by the numbers
Z = 19 fixes the protons; the neutron count can vary between isotopes, which is why the atomic mass is an average (39.098 u) rather than a round number.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 19 |
| Relative atomic mass | 39.098 u |
| Protons | 19 |
| Neutrons (commonest isotope) | 20 |
| Electrons | 19 |
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 (39.098). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Potassium a whole number?
No. 39.098 u is the average of Potassium'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 Potassium have?
Neutrons = mass number − atomic number. For Potassium's commonest isotope that is about 39 − 19 = 20, though the exact count differs between isotopes.