About

Fermium, the 100th element on the periodic table, is named after Enrico Fermi, a pioneer of the nuclear age. Like einsteinium, it was discovered in the fallout of the first hydrogen bomb test. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and thus the last element that can be prepared in macroscopic quantities, although none has been prepared yet. It has no applications beyond basic research.

Atomic Properties

Atomic Number100

Atomic Weight257 u

Neutrons (common)157

Electron Configuration[Rn] 5f¹² 7s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f¹² 7s²

Electrons per Shell2, 8, 18, 32, 30, 8, 2

Electronegativity1.3

Electron Affinity34 kJ/mol

Oxidation States+2, +3

Ionic Radius90.1 pm

Periodic Table Position

Group3

Period7

BlockF

Chemical SeriesActinoids

Physical Properties

State at STPsolid

Appearanceunknown, presumed metallic

Crystal Structurefcc

Thermal Properties

Melting Point1,800 K

Discovery

Discovered byAlbert Ghiorso, Stanley G. Thompson, Glenn T. Seaborg, Gregory R. Choppin, Bernard G. Harvey

Discovery Year1,952

Occurrencesynthetic

CAS Number7440-72-4

Electron Configuration

Energy

↿⇂

1s

↿⇂

2s

↿⇂

2p

↿⇂

3s

↿⇂

3p

↿⇂

4s

↿⇂

3d

↿⇂

4p

↿⇂

5s

↿⇂

4d

↿⇂

5p

↿⇂

6s

↿⇂

4f

↿⇂

5d

↿⇂

6p

↿⇂

7s

↿⇂

↿

5f

6d

7p

Isotopes of Fermium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²⁵⁷Fm	257.095100	—	100.5 d	Alpha Decay, Spontaneous Fission