ELEMENTLE

Element 109 · Transition Metal

Meitnerium

Period 7 · Group 9

Meitnerium is a chemical element with symbol Mt and atomic number 109. It is an extremely radioactive synthetic element (an element not found in nature that can be created in a laboratory). The most stable known isotope, meitnerium-278, has a half-life of 7.6 seconds.

Three reasons Meitnerium stands out

  1. 1

    Named after Austrian-Swedish physicist who was instrumental in the discovery of nuclear fission.

  2. 2

    The scientist it honours was repeatedly overlooked for a Nobel Prize despite her pivotal contributions to nuclear science.

  3. 3

    Its most stable known isotope has a half-life of only about 7 seconds.

An overdue place for Lise Meitner

Meitnerium honors physicist Lise Meitner, who helped explain nuclear fission but was excluded from the Nobel Prize awarded for its discovery. Only a small number of atoms have been made. Its expected chemistry as a heavy relative of iridium remains mostly theoretical.

Meitnerium at a glance
Atomic number / protons109
SymbolMt
Family (Elementle)Transition Metal
Classification (PubChem)Transition metal
Period7
Group9
Atomic mass (u)277.154
Standard stateBulk state not experimentally established
Electron configuration[Rn]7s2 5f14 6d7 (calculated)
Reported oxidation states9, 8, 6, 4, 3, 1
Electronegativity (Pauling)Not available
Atomic radius (pm)Not available
First ionization energy (eV)Not available
Electron affinity (eV)Not available
Density (g/cm³)Not available
Melting pointNot available
Boiling pointNot available
Discovery (PubChem)1982

Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.

Sources & further reading

PubChem: Meitnerium · Meitnerium on Wikipedia

The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.