FERMIUM

Introduction

Atomic Number: 100
Group: None
Atomic Weight: 257
Period: 7
CAS Number: 7440-72-4

Classification

Chalcogen
Halogen
Noble Gas
Lanthanoid
Actinoid
Rare Earth Element
Platinum Group Metal
Transuranium
No Stable Isotopes
Solid
Liquid
Gas
Solid (Predicted)

Description • Uses/Function

Fermium, the eighth transuranium element of the actinide series to be discovered, was identified by Ghiorso and co-workers in 1952 in the debris from a thermonuclear explosion in the Pacific in work involving the University of California Radiation Laboratory, the Argonne National Laboratory, and the Los Alamos Scientific Laboratory. The isotope produced was the 20-hour 255Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded 238U with 16O ions, and isolated a 30-min a-emitter, which they ascribed to 250Fm, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. The chemical properties of fermium have been studied solely with tracer amounts, and in normal aqueous media only the (III) oxidation state appears to exist. The isotope 254Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements such as plutonium by a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. Twenty isotopes and isomers of fermium are known to exist. 257Fm, with a half-life of about 100.5 days, is the longest lived. 250Fm, with a half-life of 30 min, has been shown to be a product of decay of Element 254No. It was by chemical identification of 250Fm that production of nobelium was confirmed. 1

Physical Properties

Melting Point:2*  1527 °C = 1800.15 K = 2780.6 °F
Boiling Point:2
Sublimation Point:2 
Triple Point:2 
Critical Point:2 
Density:   g/cm3

* - at 1 atm

Electron Configuration

Electron Configuration:  *[Rn] 7s2 5f12
Block: f
Highest Occupied Energy Level: 7
Valence Electrons: 2

Quantum Numbers:

n = 5
ℓ = 3
m = 1
ms = -½

Bonding

Ionization Potential   eV 3  kJ/mol  
Ionization Potential   eV 3  kJ/mol  
Ionization Potential   eV 3  kJ/mol  
1 6.5    627.2

Isotopes

Nuclide Mass 4 Half-Life 4 Nuclear Spin 4 Binding Energy
242Fm 242.07343(43)# 0.8(2) ms 0+ 1,809.82 MeV
243Fm 243.07435(23)# 210(60) ms [0.18(+8-4) s] 7/2-# 1,817.89 MeV
244Fm 244.07408(30)# 3.3(5) ms 0+ 1,825.96 MeV
245Fm 245.07539(30)# 4.2(13) s 1/2+# 1,834.03 MeV
246Fm 246.07530(4) 1.1(2) s 0+ 1,842.10 MeV
247Fm 247.07685(15)# 29(1) s (7/2+) 1,850.17 MeV
248Fm 248.077195(13) 36(2) s 0+ 1,858.24 MeV
249Fm 249.07903(11)# 2.6(7) min (7/2+)# 1,866.32 MeV
250Fm 250.079521(13) 30(3) min 0+ 1,874.39 MeV
251Fm 251.081575(9) 5.30(8) h (9/2-) 1,873.14 MeV
252Fm 252.082467(6) 25.39(4) h 0+ 1,881.21 MeV
253Fm 253.085185(4) 3.00(12) d (1/2)+ 1,889.29 MeV
254Fm 254.0868542(30) 3.240(2) h 0+ 1,897.36 MeV
255Fm 255.089962(5) 20.07(7) h 7/2+ 1,905.43 MeV
256Fm 256.091773(8) 157.6(13) min 0+ 1,904.19 MeV
257Fm 257.095105(7) 100.5(2) d (9/2+) 1,912.26 MeV
258Fm 258.09708(22)# 370(14) μs 0+ 1,920.33 MeV
259Fm 259.1006(3)# 1.5(3) s 3/2+# 1,919.08 MeV
260Fm 260.10268(54)# 1# min 0+ 1,927.16 MeV
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 4

Abundance

Safety Information


Material Safety Data Sheet - ACI Alloys, Inc.

For More Information

External Links:

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:12.
(2) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(7) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).