Fermium

Fermium was also discovered in H-bomb test debris (1952) and named after the physicist Enrico Fermi, who built the first nuclear reactor. Like einsteinium, it was found in the debris from the Ivy Mike hydrogen bomb test by secret chemical analysis.

• Atomic Number100100 protons, 100 electrons
• Atomic Mass257.09511 u100× heavier than hydrogen
• State at Room TempSolidSolid
• DensityNot measured
• Melting / Boiling1526.8°C
• Discovered1952

What is Fermium?

Fermium has 100 protons. Its most stable isotope, Fm-257, has a half-life of 100.5 days. Fermium cannot be produced in sufficient quantities to observe macroscopically, only approx. 3 billionths of a gram have ever been made. Named after Enrico Fermi. Discovered in 1952 in H-bomb test debris; announced in 1955.

Fact Fermium is element 100, symbol Fm. 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 Fermium

On Earth

Fermium 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 Fermium

At element 100, practical applications are limited by the extreme difficulty of production and the intense radioactivity. Fermium has 100 protons

How it was discovered

Fermium has 100 protons. Its most stable isotope, Fm-257, has a half-life of 100.5 days. Fermium cannot be produced in sufficient quantities to observe macroscopically, only approx. 3 billionths of a gram have ever been made. Named after Enrico Fermi. Discovered in 1952 in H-bomb test debris; announced in 1955.

Deeper dive: fermium 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 101 protons brings us to the next element on the periodic table.