Mendelevium

The first element made and identified one atom at a time, and an American tribute to Dmitri Mendeleev in the middle of the Cold War.

At a glance

Symbol: Md
Atomic number: 101
Mass number of its longest-lived isotope: [258]
Group: none; it sits in the actinide row below the table
Period: 7
Family: actinide
Electron configuration: [Rn] 5f¹³ 7s²
Electronegativity: 1.30
Common ions: Md³⁺, and also Md²⁺
Isotopes: none are stable; ²⁵⁸Md lasts longest, about 51 days

On the table

Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.

Electrons and bonding

Radioactive, like every actinide. It gives up electrons to form positive ions.

Properties

State at 25 °C: solid
What it looks like: never made in visible amounts; expected to be a metal
Melting point: 827 °C (predicted)
Boiling point: not known
Density: not measured

Where it is found

Not found in nature; made a few atoms at a time in particle accelerators.

Discovery and name

Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg made it in 1955 at Berkeley by bombarding einsteinium with alpha particles, identifying it from just 17 atoms. Naming it after the Russian creator of the periodic table during the Cold War was a notable gesture.

What it is used for

Research only.

Handle with care

Radioactive; it has only ever existed a few atoms at a time.