101MdMendelevium[258]

A real sample of the element Mendelevium — Synthetic element — no real sample has ever been photographed

Mendelevium (Md)

“The element named in honour of Dmitri Mendeleev — discovered in 1955 with just seventeen atoms, one at a time.”

View period 7 →See in trends →

Atomic number101

Atomic mass[258]

Groupf-block

Period7

BlockF-block

PhaseSolid

Electron structure

How its electrons are arranged

[Rn] 5f¹³ 7s²

Shell 1

2e⁻

Shell 2

8e⁻

Shell 3

18e⁻

Shell 4

32e⁻

Shell 5

31e⁻

Shell 6

8e⁻

Shell 7

2e⁻

Computed from the aufbau principle, with known real-world exceptions applied automatically.

🎯 Exam focus

Questions to practise

Try each question yourself first — then open it to read the full model answer.

1Whose Berkeley team created mendelevium in 1955, and which two nuclei were smashed together in the 60-inch cyclotron to make it?

Model answerGlenn Seaborg’s team at the University of California’s Radiation Laboratory in Berkeley — Albert Ghiorso, Bernard Harvey, Gregory Choppin and Stanley Thompson beside him. In the 60-inch cyclotron they smashed alpha particles (helium-4 nuclei) into a target of einsteinium-253; the fusion of those two nuclei produced the first mendelevium atoms of 1955.

2Why is mendelevium valuable for testing how the +2 and +3 oxidation states compete among the heaviest actinides?

Model answerBecause mendelevium’s +2 state is unexpectedly stable for an actinide — it behaves a little like the lanthanide ytterbium — while its neighbours lean on +3. Measuring where Md stands between the two states gives chemists a benchmark: a fixed point for mapping how the +2/+3 balance shifts along the heaviest f-block row.

3Explain how the 2019 International Year of the Periodic Table connects to the element named after Mendeleev himself.

Model answerThe 2019 International Year of the Periodic Table, run by UNES $\mathrm{CO}$ , celebrated the 150th anniversary of Mendeleev’s 1869 table. The element that carries his name is the celebration’s perfect emblem: mendelevium in the actinide row quietly honours the very architect whose table made the search for elements possible, and every periodic-table poster carrying Md joined that anniversary.

4How many atoms of mendelevium existed when the discovery was announced, and what does that reveal about how it must be studied?

Model answerSeventeen atoms — that was the entire stock at the announcement, chemically separated by ion-exchange chromatography. Such scarcity dictates the method: mendelevium must be studied one atom at a time, reading the radiation each lone atom gives off; no visible sample can ever be weighed or photographed, so atom-at-a-time chemistry is the only way.

5Mendelevium belongs to the f-block actinide series of Period 7, outside the main table — explain why the actinides are placed there.

Model answerThe actinides’ differentiating electrons fill the 5f subshell, exactly as the lanthanides above fill 4f — and fourteen such elements cannot be squeezed into Period 7’s main body without wrecking the table’s shape. So they hang in their own row below the chart, a second f-block series running from actinium to lawrencium, as Seaborg’s 1944 actinide concept proposed, with mendelevium near its end.

6Dmitri Mendeleev died in 1907, half a century before this element existed — why did Seaborg’s team still name element 101 after him?

Model answerThe tribute honoured what Mendeleev made possible: his periodic table turned element-hunting from accident into prediction, and every transuranium discovery — the Berkeley team’s own included — was guided by that framework. Naming element 101 after the table’s architect, half a century after his death in 1907, was the team’s way of crediting him for the very search itself.

Quick answers

One fact, one page

Every key fact of this element has its own clean page — a direct two-line answer first, then the working. Fast to load, easy to share.

Electron configurationThe full arrangement, step by step ValencyHow many bonds it forms Atomic massThe standard weight, explained Metal or nonmetalWhich family it belongs to Everyday usesWhere you meet it daily

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Study

The notes

About the element

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.

Appearance

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.

Real world

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

UNES $\mathrm{CO}$ ’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.

Story

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.

Name originHonours Dmitri Mendeleev, father of the periodic table.

Neighbours

Nearby elements

The elements that sit right beside this one on the table — often the closest chemical cousins.

99EsEinsteinium[252]100FmFermium[257]102NoNobelium[259]103LrLawrencium[262]