101 Md (258)

Mendelevium

Actinide Mendelevium solid Radioactivity

[Rn] 5f¹³ 7s² · 2 · 8 · 18 · 32 · 31 · 8 · 2

← Fm Fermium No Nobelium →

The element named after the author of the periodic law. Mendelevium was made by bombarding a target of just a thousand einsteinium atoms and detecting one atom per experiment.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 101
Atomic mass: 258 а.е.м. ≈
Electron configuration: [Rn] 5f¹³ 7s²
Electrons per shell: 2 · 8 · 18 · 32 · 31 · 8 · 2
Block: f-block
Group: no data
Period: 7
Electronegativity (Pauling): 1.3
Electronegativity (Allen): 1.3
Atomic radius: 246 pm
Covalent radius: 173 pm
Van der Waals radius: 246 pm
Ionisation energy 1: 635 kJ/mol
Electron affinity: 93.9 kJ/mol
Common oxidation states: +3
Oxidation states: +2, +3

Physical properties

State at 25 °C: solid
Density: 10.3 g/cm³ ≈
Melting point: 1 100 K · 826.9 °C ≈
Boiling point: no data
Speed of sound: no data

Thermal properties

Heat of fusion: no data
Heat of vaporisation: no data
Specific heat capacity: no data
Thermal conductivity: no data

Mechanical properties

Young's modulus: no data
Shear modulus: no data
Bulk modulus: no data
Poisson ratio: no data
Mohs hardness: no data
Brinell hardness: no data

Electrical and magnetic properties

Electrical resistivity: no data
Magnetic ordering: paramagnetic
Curie point: no data
Néel point: no data
Superconducting point: no data

Crystal structure

Crystal structure: face-centred cubic (fcc)
Lattice constants: no data

Abundance

In the crust: 0 mg/kg
In the ocean: 0 mg/L
In the universe: 0 mg/kg
In the human body: 0 mg/kg

Isotopes

Isotope	Abundance	Half-life	Decay mode
²⁵⁸Md	—	51.5 d	α
²⁶⁰Md	—	31.83 d	СД

Mendelevium-258, half-life 51.5 days, is the longest-lived. Mendelevium-256, the first made, lives 77 minutes.

Discovery

Year of discovery: 1955
Discovered by: Ghiorso, Harvey, Choppin, Thompson and Seaborg
Where: Berkeley, USA
Origin of the name: after Dmitri Mendeleev, author of the periodic law

History

Ghiorso, Harvey, Choppin, Thompson and Seaborg synthesised mendelevium at Berkeley in 1955. The first run produced seventeen atoms. The name drew objections at the height of the Cold War but was accepted.

Where it occurs

Absent from nature.

How it is produced

By alpha bombardment of einsteinium in an accelerator. It is made one atom at a time.

Role in living things

No biological role.

Safety

Only single atoms are ever handled.

Uses

Fundamental research: mendelevium was the first element whose chemistry was studied at the single-atom level

Curiosities

Mendelevium honours Dmitri Mendeleev — the only element named after the author of the table itself.
The recoil technique developed for mendelevium became the standard for all subsequent superheavy chemistry.
The first experiment registered seventeen atoms, one at a time.
Proposing a Russian scientist's name in 1955 was a deliberate political gesture by American physicists.