Fermium. A man-made radioactive actinide with atomic symbol fm, atomic number 100, and atomic weight 257. Its known isotopes range from 244-254 and 256-258. Its valence can be +2 or +3. Like einsteinium, it was discovered in 1952 in the debris from a thermonuclear explosion.
Chemical name: Fermium
(12 Dec 1998)
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