Meitnerium
Meitnerium is a synthetic, radioactive group-9 element; much of its chemistry remains predicted rather than measured.
Meitnerium marks the meeting point of nuclear physics and the limits of measurement.
Explore Meitnerium's atom- Atomic number
- 109
- Source isotope mass
- 277.154 u
- Family
- Transition metal
- Period
- 7
- Group
- 9
- Standard state
- Predicted solid
In everyday life
Meitnerium has no everyday uses; its properties are studied or predicted.
Something to remember
Meitnerium was named after Lise Meitner.
Meet its electrons
[Rn] 7s2 5f14 6d7 (calculated)
Published theoretical assignment for a superheavy neutral atom; bulk properties and some orbital assignments remain uncertain.
Electrons per shell: 2 · 8 · 18 · 32 · 32 · 15 · 2.
The playground shows an illustrative shell model. Real electrons are described by quantum orbitals, rather than tiny planets traveling along fixed paths.
A connection to explore
Meitnerium occupies the same group as iridium, but many of its properties remain predicted.
Meet Iridium (Ir)Properties and conditions
- Source isotope mass
- 277.154 uPubChem value for an element without stable isotopes. This is not a standard atomic weight and may be rounded to an isotope mass number; uncertainty is not supplied. CIAAW assigns no standard atomic weight to this element. The PubChem isotope is not necessarily the longest-lived isotope.PubChem periodic table ↗ · Retrieved 2026-10-15
- Standard state
- Predicted solidPrediction · PubChem classification, including explicit predictions where stated. Reference temperature and pressure are not supplied in the table.PubChem periodic table ↗ · Retrieved 2026-10-15
- First ionisation energy
- Not reportedEnergy to remove the first electron from an isolated neutral gas-phase atom. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electronegativity
- Not reportedA dimensionless relative measure; values depend on the chosen scale. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Melting point
- Not reportedPubChem reported value. Pressure, allotrope and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Boiling point
- Not reportedPubChem reported value. Pressure and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Density
- Not reportedPubChem reported value. Temperature, pressure, allotrope and measurement uncertainty are not specified in the table; gas densities are especially condition-dependent.PubChem periodic table ↗ · Retrieved 2026-10-15
- Oxidation states
- 9, 8, 6, 4, 3, 1Prediction · Selected PubChem oxidation states; formal electron bookkeeping, not a list of stable free-ion charges or every possible compound.PubChem periodic table ↗ · Retrieved 2026-10-15
- Discovery
- 1982PubChem discovery attribution. Ancient knowledge and competing priority claims cannot always be represented by a single year.PubChem periodic table ↗ · Retrieved 2026-10-15
- Atomic radius
- Not reportedPubChem tabulated radius. Radius definitions depend on bonding and convention; measurement definition and uncertainty are not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electron affinity
- Not reportedPubChem reported gas-phase electron affinity. Sign conventions and electronic states matter; uncertainty is not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
Isotopes, abundance and decay
Isotopes share a proton count but have different neutron counts. This selection includes naturally tabulated compositions and a reference isotope for other elements. It is not a list of every known isotope.
Explore 1 isotope of Mt
| Isotope | Relative atomic mass | Natural fraction | Half-life | Decay |
|---|---|---|---|---|
| Mt-279Reference isotope | 279.15808(72#) | Not tabulated | 20# s · estimated | A ?;SF ? |
Fractions use NIST’s terrestrial isotopic compositions, which can vary by sample. Parentheses denote uncertainty in the last digits. Half-lives and decay branches use NUBASE2020; # marks estimates, >/< mark limits. “No decay observed” follows that evaluation and does not prove permanent stability. Decay branch intensities are percentages; SF means spontaneous fission, EC electron capture, IT an isomeric transition.
Follow the science
Use these original references to explore the data and context. Atomic weights can vary with isotope composition; values for elements without stable isotopes may describe a representative isotope rather than a standard atomic weight.