Atomic Mass of Boron (B)
The relative atomic mass of Boron is 10.81 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 Boron. 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 Boron page is one click away.
Boron by the numbers
Z = 5 fixes the protons; the neutron count can vary between isotopes, which is why the atomic mass is an average (10.81 u) rather than a round number.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 5 |
| Relative atomic mass | 10.81 u |
| Protons | 5 |
| Neutrons (commonest isotope) | 6 |
| Electrons | 5 |
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 (10.81). Exams love this one-mark distinction.
Students also ask
Is the atomic mass of Boron a whole number?
No. 10.81 u is the average of Boron'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 Boron have?
Neutrons = mass number − atomic number. For Boron's commonest isotope that is about 11 − 5 = 6, though the exact count differs between isotopes.