Mendelevium (Md)
Mendelevium (symbol Md) is the chemical element with atomic number 101: an actinide, solid at 0 °C, radioactive, made artificially, with an atomic mass of 258 u. Discovered in 1955 (Albert Ghiorso et al.).
Mendelevium is named after Dmitri Mendeleev, the Russian chemist who devised the periodic table in 1869. It was the first element discovered literally one atom at a time: just 17 atoms in the 1955 experiment. It can no longer be produced in a reactor; a particle accelerator is required. Its most stable isotope, mendelevium-258, has a half-life of about 51 days.
Key facts
- Atomic number
- 101
- Symbol
- Md
- French name
- Mendélévium
- Atomic mass
- 258 u
- Molar mass
- [258] g/mol
- Family
- Actinides
- Position
- period 7, f-block
- State at 0 °C
- Solid
- Melting point
- 826.9 °C
- Electronegativity (Pauling)
- 1.3
- First ionization energy
- 635 kJ/mol
- Electron configuration
- [Rn] 5f¹³ 7s²
- Radioactive
- yes
- Discovery
- 1955, Albert Ghiorso et al.
Origin of the name
In honor of Dmitri Mendeleev, father of the periodic table.
What does mendelevium look like?
Never observed in visible amounts. Calculations suggest a silvery metal, perhaps closer to the alkaline earth metals than one would expect.
Where is mendelevium found?
Absent from nature. It has only ever existed as isolated atoms in the lab.
How is mendelevium produced?
A tiny einsteinium-253 target is bombarded with alpha particles (helium nuclei) in a cyclotron, an accelerator that whirls particles along a spiral path to speed them up. Every so often, a particle fuses with an einsteinium nucleus and forms an atom of mendelevium.
Top producers
- United States (Berkeley)
What is mendelevium used for?
- Basic research only
- Studying the chemical properties of the heaviest elements
In everyday life
- None — it lasts only days in the lab, atom by atom
Role in living things
No biological role.
Hazards of mendelevium
Radioactive, but produced in so few atoms that it poses no practical danger.
Cosmic origin
- Human-made: Does not exist (or barely) in nature: synthesized in a reactor or accelerator.
History of mendelevium
In 1955, Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg bombarded about a billion einsteinium atoms with alpha particles in the Berkeley cyclotron. Over several nights of experiments, they detected 17 atoms of the new element. At the height of the Cold War, Seaborg had to ask the US government for permission to name it after a Russian scientist.
Did you know?
- The researchers had wired their detector to a bell that rang each time an atom of the new element decayed.
- It is the only element named after the inventor of the periodic table himself — and Mendeleev had predicted the existence of elements still unknown.
- It was the first element identified chemically when only a handful of atoms were available.
Isotopes of mendelevium
No stable isotopes; mendelevium was the first element created one atom at a time, in a particle accelerator, in 1955.
- mendelevium-256: radioactive, half-life 1.28 h. The element's first synthesized isotope, in 1955: just 17 atoms.
- mendelevium-258: radioactive, half-life 51.6 days. The longest-lived of the well-characterized isotopes.
Related elements
Same family (actinides): Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Berkelium (Bk), Californium (Cf), Einsteinium (Es), Fermium (Fm), Nobelium (No), Lawrencium (Lr).