Mendelevium (Md)
“The element named in honour of Dmitri Mendeleev — discovered in 1955 with just seventeen atoms, one at a time.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- A fully synthetic, intensely radioactive actinide; even its longest-lived isotope Md-258 decays away in about 51 days.
- The first element in history discovered one atom at a time — the original seventeen atoms were fished out chemically, not seen directly.
- Unusual oxidation chemistry for an actinide: the +2 state is unexpectedly stable, so Md behaves a little like the lanthanide ytterbium.
- Sits in Period 7 among the actinides of the f-block; it can only be made in particle accelerators and vanishes from any sample quickly.
No one has ever seen a visible piece of mendelevium — in all history only a few thousand atoms have been made. It is predicted to be a silvery, fiercely radioactive actinide metal like its neighbours, but no sample has ever been large enough to weigh or photograph.
Where you meet it
✦ Uses
- Fundamental research in actinide chemistry — Md is a benchmark for how the balance between +2 and +3 oxidation states shifts along the heaviest f-block row.
- Nuclear-structure studies: the alpha and spontaneous-fission decays of its isotopes help test shell-model predictions around Z = 100.
- Advancing atom-at-a-time technique — the 1955 separation of seventeen Md atoms pioneered methods still used for superheavy elements today.
◍ Everyday examples
- UNESCO’s International Year of the Periodic Table in 2019 celebrated 150 years of Mendeleev’s table — the very table that gives this element its name.
- Any modern periodic-table poster or NCTB chemistry chapter carries Md in the actinide row, quietly honouring the table’s creator.
History & name
In 1955 a team at the University of California’s Radiation Laboratory in Berkeley — Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Nobel laureate Glenn Seaborg — bombarded einsteinium-253 with alpha particles in the 60-inch cyclotron. After hours of bombardment they chemically separated just seventeen atoms of a brand-new element using ion-exchange chromatography. They named it mendelevium after Dmitri Mendeleev, the architect of the periodic table, as a tribute to the man who made the very search for elements possible.