ELEMENTLE

Element 101 · Actinide

Mendelevium

Period 7

Mendelevium is a synthetic element with chemical symbol Md (formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the antepenultimate actinide and the ninth transuranic element.

Three reasons Mendelevium stands out

  1. 1

    Synthetic element, named after the famous Russian chemist who formulated the first periodic table.

  2. 2

    When it was first synthesised in 1955, only 17 atoms were produced in the entire experiment.

  3. 3

    It was the first element to be produced one atom at a time and then chemically identified.

Seventeen atoms and a clear chemical signal

The first mendelevium experiment produced only about seventeen atoms, yet researchers chemically separated their decay products and proved a new element existed. Naming it for Dmitri Mendeleev honored the periodic framework that predicted missing elements long before atom-at-a-time chemistry became possible.

Mendelevium at a glance
Atomic number / protons101
SymbolMd
Family (Elementle)Actinide
Classification (PubChem)Actinide
Period7
GroupLanthanide / actinide series
Atomic mass (u)258.09843
Standard stateBulk state not experimentally established
Electron configuration[Rn]7s2 5f13
Reported oxidation states+3, +2
Electronegativity (Pauling)1.3
Atomic radius (pm)Not available
First ionization energy (eV)6.58
Electron affinity (eV)Not available
Density (g/cm³)Not available
Melting point1100 K (826.85 °C) · estimated
Boiling pointNot available
Discovery (PubChem)1955

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: Mendelevium · Mendelevium 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.