Atomic Properties of Fm
- Atomic Number of Fm
- 100
- Atomic Mass of Fm
- 257.0000 u
- Electron Configuration
- [Rn] 5f12 7s2
- Electronegativity
- 1.30
- Block
- f-block
- Group
- —
- Period
- 7
Fermium entered science through a filter paper carrying almost unimaginably small evidence. After the first thermonuclear test in 1952, researchers collected debris and separated its radioactive components. Among them they identified atoms with atomic number 100. The intense neutron flux had driven uranium nuclei through repeated neutron captures and beta decays, building an element heavier than any then found in nature.
The discovery was initially classified because it came from weapons-test data. When the result could be discussed openly, the element was named for Enrico Fermi, whose work helped establish nuclear and neutron physics. Its symbol, Fm, marks a scientific legacy attached to a substance that cannot be gathered into an ordinary sample.
Fermium is a synthetic actinide. All its isotopes are radioactive, and even fermium-257, the longest-lived known isotope, survives for only about 100 days. Researchers can produce fermium by irradiating lighter transuranium elements with neutrons or other particles, but only tiny quantities result. There is no practical commercial application; the atoms are valuable because their decay and chemistry test models of very heavy nuclei and late-actinide behavior.
Here the Corebound archetype becomes literal. Extra protons make the nucleus harder to hold together, and every observed decay supplies another clue about that balance. Fermium's importance is not the amount made. It is the chain of reasoning that lets scientists find atomic number 100 in debris, identify it through radiation, and extend the map of matter one scarce atom at a time.