Mendelevium (Md)

Mendelevium was the first element made and identified one atom at a time. The Berkeley team bombarded about a billion einsteinium atoms with alpha particles and expected roughly one mendelevium atom per experiment; they ran it seventeen times and detected seventeen atoms, catching each on a gold foil and identifying it by the way it decayed. Naming it after Dmitri Mendeleev was politically awkward in 1955, honouring a Russian at the height of the Cold War, and the Berkeley group had to argue the point.

Properties

Atomic number

101

Symbol

Md

Mass number of most stable isotope

[258]

Category

Actinide

Period

7

Block

f-block

Electron configuration

[Rn] 7s² 5f¹³

Electrons per shell

2, 8, 18, 32, 31, 8, 2

Oxidation states

+3, +2

Discovered

1955 by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹³

Noble gas shorthand

[Rn] 7s² 5f¹³

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 31 · P: 8 · Q: 2

What it is used for

• Research only; no application outside the laboratory

Hazards

• Intensely radioactive; only a few million atoms have ever been made

Melting point, boiling point, density and electronegativity are omitted: no measured values exist, only extrapolations. The mass given is the mass number of mendelevium-258, the longest-lived at 51.5 days.

Several physical properties are not listed for mendelevium because no bulk sample has ever existed. Only a handful of atoms have been produced, often with half-lives measured in seconds, so published melting points and densities for elements in this range are calculations rather than measurements. They are omitted rather than presented as observed values.

Neighbours in the table