Atomic Mass of Meitnerium (Mt)
Meitnerium has no stable isotope, so no standard atomic weight exists; its most stable isotope has mass number ≈ 278, and the bracketed value [278] marks that estimate.
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 Meitnerium page is one click away.
Meitnerium by the numbers
Z = 109 fixes the protons; the neutron count can vary between isotopes, which is why the atomic mass is an average ([278] u) rather than a round number.
| Quantity | Value |
|---|---|
| Atomic number (Z) | 109 |
| Relative atomic mass | [278] (no stable isotope) |
| Protons | 109 |
| Neutrons (commonest isotope) | 169 |
| Electrons | 109 |
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 ([278] is shown in brackets because it is only an estimate). Exams love this one-mark distinction.
Why is the mass in brackets?
Every isotope of Meitnerium is radioactive and vanishes too quickly to build up a natural mixture — so the IUPAC convention prints the mass number of the longest-lived isotope in square brackets instead of a standard atomic weight.
Students also ask
Is the atomic mass of Meitnerium a whole number?
No — Meitnerium has no stable isotopes, so chemists use the bracketed estimate [278] rather than a measured average.
How many neutrons does Meitnerium have?
Neutrons = mass number − atomic number. For Meitnerium's commonest isotope that is about 278 − 109 = 169, though the exact count differs between isotopes.