Mendelevium

Mendelevium was the first element to be made one atom at a time in a cyclotron bombardment, only 17 atoms were produced in its discovery experiment in 1955. Named after Dmitri Mendeleev, who created the periodic table that predicted so many of these elements' existence.

• Atomic Number101101 protons, 101 electrons
• Atomic Mass258.09843 u101× heavier than hydrogen
• State at Room TempSolidSolid
• DensityNot measured
• Melting / Boiling826.9°C
• Discovered1955

What is Mendelevium?

Mendelevium has 101 protons. Its most stable isotope, Md-258, has a half-life of 51.5 days. Only microgram amounts have ever been made. The chemistry of Md³⁺ has been studied using a few atoms at a time. Produced in 1955 at Berkeley by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg.

Fact Mendelevium is element 101, symbol Md. As an actinide, it is part of the f-block of the periodic table: one of 15 radioactive elements from actinium (89) to lawrencium (103). All actinides are radioactive; none has a stable isotope. They are produced in nuclear reactors and by decay of heavier elements, and their chemistry has been studied using only microgram or nanogram quantities.

Where you find Mendelevium

On Earth

Mendelevium does not occur in significant natural abundance. It is produced only artificially, by bombarding heavier actinide targets with neutrons or lighter ions in nuclear reactors or particle accelerators. World production is measured in nanograms or picograms, a few billion atoms at most per year.

How we use Mendelevium

At element 101, practical applications are limited by the extreme difficulty of production and the intense radioactivity. Mendelevium has 101 protons

How it was discovered

Mendelevium has 101 protons. Its most stable isotope, Md-258, has a half-life of 51.5 days. Only microgram amounts have ever been made. The chemistry of Md³⁺ has been studied using a few atoms at a time. Produced in 1955 at Berkeley by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg.

Deeper dive: mendelevium and the actinide series

The actinides (elements 89-103) form the lower of the two rows below the main body of the periodic table. They represent the filling of the 5f electron subshell. Unlike the lanthanides (the upper row), the actinides show greater variety in their chemistry because the 5f, 6d and 7s orbitals are close in energy. The early actinides, thorium through neptunium, can show many different oxidation states (e.g. uranium from +3 to +6). The heavier actinides increasingly resemble the lanthanides in preferring the +3 state.

All actinides beyond bismuth (83) are radioactive. The lightest, thorium, protactinium and uranium, have long enough half-lives to survive from the formation of the solar system. Neptunium and beyond are almost entirely synthetic, produced in nuclear reactors or accelerators. The transuranic elements were created at remarkable facilities including Oak Ridge National Laboratory, the Berkeley Cyclotron, the GSI in Darmstadt and JINR in Dubna.

Moving to 102 protons brings us to the next element on the periodic table.