Fermium

Fermium, ₁₀₀Fm

Fermium
Pronunciation	/ˈfɜːrmiəm/ ​(FUR-mee-əm)
Mass number	[257]
Fermium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Er ↑ Fm ↓ — einsteinium ← fermium → mendelevium
Atomic number (Z)	100
Group	f-block groups (no number)
Period	period 7
Block	f-block
Electron configuration	[Rn] 5f12 7s2
Electrons per shell	2, 8, 18, 32, 30, 8, 2
Physical properties
Phase at STP	solid (predicted)
Melting point	1800 K ​(1500 °C, ​2800 °F) (predicted)
Density (near r.t.)	9.7(1) g/cm3 (predicted)
Atomic properties
Oxidation states	common: +3 +2
Electronegativity	Pauling scale: 1.3
Ionization energies	1st: 629 kJ/mol
Other properties
Natural occurrence	synthetic
Crystal structure	​face-centered cubic (fcc) (predicted)
CAS Number	7440-72-4
History
Naming	after Enrico Fermi
Discovery	Lawrence Berkeley National Laboratory (1953)
Isotopes of fermium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 252Fm synth 25.39 h SF – α 248Cf 253Fm synth 3 d ε 253Es α 249Cf 255Fm synth 20.07 h SF – α 251Cf 257Fm synth 100.5 d α 253Cf SF –

Fermium (Template:Pron-en, FER-mee-əm) is a synthetic element with the symbol Fm and atomic number 100. A highly radioactive metallic transuranic element of the actinide series, fermium is made by bombarding plutonium with neutrons and is named after nuclear physicist Enrico Fermi. Fermium is the eighth transuranic element.

Characteristics

Electron shell diagram of fermium

Only small amounts of fermium have been produced or isolated. Thus, relatively little is known about its chemical properties. Only the (III) oxidation state of the element appears to exist in aqueous solution. ²⁵⁴Fm and heavier isotopes can be synthesized by intense neutron bombardment of lighter elements (especially uranium and plutonium). During this, successive neutron captures mixed with beta decays build the fermium isotope. The intense neutron bombardment conditions needed to create fermium exist in thermonuclear explosions and can be replicated in the laboratory (such as in the High Flux Isotope Reactor at Oak Ridge National Laboratory). The synthesis of element 102 (nobelium) was confirmed when ²⁵⁰Fm was chemically identified. Like all synthetic elements, it is extremely radioactive and highly toxic.

Uses

There are no known uses of fermium outside of basic research.

History

Fermium (after Enrico Fermi) was first discovered by a team led by Albert Ghiorso in 1952. The team found ²⁵⁵Fm in the debris of the first hydrogen bomb explosion (see Operation Ivy). That isotope was created when ²³⁸U combined with 17 neutrons in the intense temperature and pressure of the explosion (eight beta decays also occurred to create the element). The work was overseen by the University of California Radiation Laboratory, Argonne National Laboratory, and Los Alamos Scientific Laboratory. All these findings were kept secret until 1955 due to Cold War tensions. Samples of sea coral impacted from the first thermonuclear explosion of November 1952 were used.

In late 1953 and early 1954 a team from the Nobel Institute of Physics in Stockholm bombarded a ²³⁸U target with ¹⁶O ions, producing an alpha-emitter with an atomic weight of ~250 and with 100 protons (in other words, element ²⁵⁰Unn). The Nobel team did not claim discovery until 1954. The isotope they produced was later positively identified as ²⁵⁰Fm.

Isotopes

17 radioisotopes of fermium have been characterized, with the most stable being ²⁵⁷Fm with a half-life of 100.5 days, ²⁵³Fm with a half-life of 3 days, ²⁵²Fm with a half-life of 25.39 hours, and ²⁵⁵Fm with a half-life of 20.07 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.4 hours, and the majority of these have half-lives that are less than 3 minutes. This element also has 1 meta state, ^250mFm (t_½ 1.8 seconds). The isotopes of fermium range in atomic weight from 242.073 u (²⁴²Fm) to 259.101 u (²⁵⁹Fm).

References

• Los Alamos National Laboratory - Fermium
• Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1
• It's Elemental - Fermium

External links

• WebElements.com - Fermium