Meitnerium (Mt)
Element 109 · Transition metal · atomic mass [278] u · group 9, period 7
Electron shells: 2, 8, 18, 32, 32, 15, 2
Meitnerium has never been produced in quantities large enough to measure any bulk property. Everything known about it comes from detecting individual decay chains.
Lise Meitner explained nuclear fission but was passed over for the Nobel — element 109 is her memorial.
- Atomic number
- 109
- Atomic mass
- [278] u
- Electron configuration
- [Rn] 7s² 5f¹⁴ 6d⁷ (calculated)
- Group · period · block
- 9 · 7 · d
- Oxidation states
- +1, +3, +4, +6, +8, +9
- Electronegativity
- Not measured
- Melting point
- —
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Unknown
- Appearance
- Unknown; presumed metallic
- Discovered
- Peter Armbruster, Gottfried Münzenberg and colleagues, 1982
109 protons, and 109 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Cobalt group
What Meitnerium is used for
- Scientific research only
Atomic structure of Meitnerium
A neutral meitnerium atom has 109 protons and 109 electrons. Its most common isotope carries about 169 neutrons, which is where the mass number 278 comes from. Change the neutron count and you have a different isotope of meitnerium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 32, 15, 2. In orbital notation that is [Rn] 7s² 5f¹⁴ 6d⁷ (calculated). As a d-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Meitnerium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Meitnerium sits in the periodic table
The d-block. Multiple stable oxidation states give them coloured compounds, catalytic ability and the strength that makes them the working metals of industry.
- Directly above: Iridium — same group, so similar chemistry with a smaller atom.
- One proton lighter: Hassium.
- One proton heavier: Darmstadtium.
Discovery and naming
Meitnerium was discovered by Peter Armbruster, Gottfried Münzenberg and colleagues in 1982. Its name comes from Lise Meitner, which is also why its symbol (Mt) does not match its English name.
Every isotope of meitnerium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Meitnerium?
Meitnerium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 278 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Meitnerium have?
Meitnerium has 109 protons, because the atomic number is the proton count and that is what makes an atom Meitnerium at all. A neutral Meitnerium atom has the same number of electrons, 109. The neutron count varies by isotope; the most common one has about 169, since 278 − 109 = 169.
What is the electron configuration of Meitnerium?
The electron configuration of Meitnerium is [Rn] 7s² 5f¹⁴ 6d⁷ (calculated). Its electrons are arranged 2, 8, 18, 32, 32, 15, 2 across 7 shells.
Is Meitnerium a metal?
Yes. Meitnerium is classified as a transition metal, on the metallic side of the table.
What group and period is Meitnerium in?
Meitnerium is in group 9 (the cobalt group), period 7, in the d-block. The group is its column and the period is its row.
What is Meitnerium used for?
Scientific research only. Meitnerium has never been produced in quantities large enough to measure any bulk property.
Who discovered Meitnerium, and where does its name come from?
Meitnerium (Mt) was discovered by Peter Armbruster, Gottfried Münzenberg and colleagues in 1982. The name comes from Lise Meitner.
Is Meitnerium radioactive?
Yes. Every isotope of Meitnerium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.