Fermium is a chemical element with an atomic number of 100 in the periodic table of elements. Being a synthetically produced radioactive substance, this lanthanide does not exist naturally in Earth’s crust. This is the heaviest synthetically produced element that has been created by bombarding lighter elements with neutrons. 

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Chemical and Physical Properties of Fermium


The symbol in the periodic table of elements: Fm

Atomic number: 100

Atomic weight (mass): 257 g.mol-1

Group number: 20 (Actinides)

Period: 7

Color: A shiny, silvery-gray metal

Physical state: Solid at room temperature

Half-life: From 730(60) µs to 100.5 days

Electronegativity according to Pauling: 1.3

Density: Unknown

Melting point: 1527°C, 2781°F, 1800 K

Boiling point: Unknown

Van der Waals radius: Unknown

Ionic radius: Unknown

Isotopes: 18

Most characteristic isotope: 257Fm

Electronic shell: [Rn] 5f11 6d1 7s2

The energy of the first ionization: Unknown

The energy of the second ionization: Unknown

Discovery date: In 1952 by Albert Ghiorso


Located between the einsteinium and mendelevium, fermium has the periodic table symbol Fm, atomic number 100, atomic mass of 257 g.mol-1, atomic radius of 290 pm, and electron configuration [Rn] 5f11 6d1 7s2. This synthetic transuranium element is a silvery-white radioactive metal that reaches its melting point at 1527°C (2781°F, 1800 K). As a member of the actinide family of elements in the periodic table, fermium has the oxidation states of +3, 2, and 3.                           

How Was Fermium Discovered?

In 1952, the teams of scientists from the Lawrence Berkeley National Laboratory, the Argonne National Laboratory, and the Los Alamos Scientific Laboratory succeeded in isolating a new transuranium element with chemical properties that had classified fermium in the family of lanthanides. 


Under the leadership of the American nuclear scientist Albert Ghiorso (1915 – 2010), the teams of scientists were assigned to analyze the radioactive debris left behind after the detonation of the first hydrogen bomb. The hydrogen bomb test happened on Elugelab Island on the Eniwetok Atoll in the South Pacific. They managed to detect the fermium-255 isotope in the material gathered from the exploded nuclear weapon. They isolated the isotope at the University of California Radiation Laboratory, Berkeley, by compounding seventeen fermium-255 neutrons with uranium-238, which have been later exposed to eight beta decay processes.


At the beginning of 1954, a research team employed at the Nobel Institute of Physics in Stockholm bombarded 238 U with 16O ions. This resulted in the isolation of an alpha emitter with a half-life of 30 minutes. By this, the scientists from the aforementioned teams were able to officially confirm the new chemical element – the fermium (Fm). The chemical identification of 250Fm isotope with a half-life of 20.07 hours also confirmed the production of nobelium, i.e. the element 102.

The “Ivy Mike” Nuclear Test

On November 1st, 1952, the U.S. Atomic Energy Commission and Department of Defense conducted the first successful test of a hydrogen fusion bomb on a Pacific atoll under the name “Operation Ivy”. The massive experimental hydrogen bomb was named “Ivy Mike”. This bomb was made of a uranium-238 isotope intended to radiate sufficient heat. In that way, a thermonuclear explosion would be produced. 


The explosive energy of the hydrogen bomb equaled 10.4 Megatons of a TNT explosive. It was produced by the fission explosion that further triggered fusion in liquid deuterium, a heavy hydrogen isotope of hydrogen. On the other hand, the flux of neutrons that affected the uranium-238 isotope generated elements of atomic numbers 93 to 100. The fermium-255 isotope was among the last produced isotopes by the explosion. 

The Manhattan Project

During World War II, the United States embarked on a project aimed at building an atomic bomb. Labeled as “The Manhattan Project”, it incorporated the previously developed “Tube Alloys” project which was organized and supported by the United Kingdom and Canada. The project resulted in the production of two types of atomic bombs: a gun-type fission weapon and the implosion-type nuclear weapon. 


The scientists included in this project gathered samples of the debris from the testing grounds for further analysis. After the war ended, these researches on the nuclear materials served for the development of the new nuclear weapons and bombs that were tested at the Bikini Atoll as part of Operation Crossroads. The “Manhattan project” also opened the doors for the establishment of a nuclear-based navy. 

How Did Fermium Get Its Name?

The element 100 of the periodic table was named fermium in honor of the Italian (later naturalized American) nuclear physicist Enrico Fermi (1901 – 1954). Dubbed the “architect of the nuclear age” and the “architect of the atomic bomb”, Fermi received the Nobel Prize in Physics in 1938 for his scientific contributions in the realm of nuclear physics and chemistry. 

This distinguished nuclear physicist was awarded for his discovery of nuclear reactions triggered by slow neutrons, providing that some of the new radioactive elements result from the irradiation of neutrons, building of the first atomic bomb, the development of the first artificial self-sustained nuclear reactor, his participation in the ‘Trinity test’, as well as for his research conducted during “Manhattan Project”. 

Where Can You Find Fermium?

This man-made radioactive chemical substance can be obtained only in microgram quantities by a neutron bombardment of plutonium in a nuclear reactor and neutron capture. 254Fm and heavier isotopes can be produced by intensely irradiating lower elements, such as plutonium. Furthermore, fermium is produced by performing multiple neutron captures in lighter elements, such as uranium and curium, after which a  beta decay of the isotopes occurs. Also, einsteinium (the element 99) sometimes undergoes a decay into fermium. 


Fermium in Everyday Life

Fermium has no application in everyday life. As a result of its short half-life and the small amounts that are produced, fermium is used exclusively in scientific research projects. 

How Dangerous Is Fermium?

The radioactive fallout from nuclear weapons testing occurs after the detonation of a nuclear weapon. The ‘mushroom’ shaped cloud of debris that rises up in the air and spreads in a wide diameter in the environment contains a great number of super-heavy radioactive elements, such as uranium, fermium, europium, americium, cesium, strontium, etc. The heavier particles fall to the ground, while the lighter radioactive particles spread in the atmosphere. In this way, they can circulate in the air for a long time and impose a risk of exposure to radiation. 


Apart from the toxic effects that may occur due to its radioactivity, fermium has no other biological role that has been determined.

Environmental Effects of Fermium

Since fermium is a man-made substance, this element does not exist in nature. Also, it’s produced in a negligible amount, so it cannot be considered an environmental threat. However, it can be traced to the locations where nuclear weapons have been tested. 

Isotopes of Fermium

All of the fermium isotopes are radioactive. Having a half-life of about 100.5 days, fermium-257 is fermium’s most stable isotope. It decays into californium-253 via alpha decay or through spontaneous fission. 



[n 1]

Z N Isotopic mass (Da)

[n 2][n 3]

Half-life Decay


[n 4]



Spin and


[n 5][n 6]

Excitation energy
241Fm 100 141 241.07421(32)# 730(60) µs SF(>78%) (various) 5/2#+
α (<14%) 237Cf
242Fm 100 142 242.07343(43)# 0.8(2) ms SF (various) 0+
α (rare) 238Cf
243Fm 100 143 243.07447(23)# 231(9) ms α (91%) 239Cf 7/2−#
SF (9%) (various)
β+ (rare) 243Es
244Fm 100 144 244.07404(22)# 3.12(8) ms SF (99%) (various) 0+
α (1%) 240Cf
245Fm 100 145 245.07535(21)# 4.2(13) s α (95.7%) 241Cf 1/2+#
β+ (4.2%) 245Es
SF (.13%) (various)
246Fm 100 146 246.075350(17) 1.54(4) s α (85%) 242Cf 0+
β+ (10%) 246Es
β+, SF (10%) (various)
SF (4.5%) (various)
247Fm 100 147 247.07695(12)# 31(1) s α (>50%) 243Cf (7/2+)
β+ (<50%) 247Es
248Fm 100 148 248.077186(9) 35.1(8) s α (93%) 244Cf 0+
β+ (7%) 248Es
SF (.10%) (various)
249Fm 100 149 249.078928(7) 1.6(1) min β+ (85%) 249Es (7/2+)#
α (15%) 245Cf
250Fm 100 150 250.079521(9) 30.4(15) min α (90%) 246Cf 0+
EC (10%) 250Es
SF (6.9×10−3%) (various)
251Fm 100 151 251.081540(16) 5.30(8) h β+ (98.2%) 251Es (9/2−)
α (1.8%) 247Cf
252Fm 100 152 252.082467(6) 25.39(4) h α (99.99%) 248Cf 0+
SF (.0023%) (various)
β+β+ (rare) 252Cf
253Fm 100 153 253.085185(4) 3.00(12) d EC (88%) 253Es (1/2)+
α (12%) 249Cf
254Fm 100 154 254.0868544(30) 3.240(2) h α (99.94%) 250Cf 0+
SF (.0592%) (various)
255Fm 100 155 255.089964(5) 20.07(7) h α 251Cf 7/2+
SF (2.4×10−5%) (various)
256Fm 100 156 256.091774(8) 157.6(13) min SF (91.9%) (various) 0+
α (8.1%) 252Cf
257Fm[n 7] 100 157 257.095106(7) 100.5(2) d α (99.79%) 253Cf (9/2+)
SF (.21%) (various)
258Fm 100 158 258.09708(22)# 370(14) µs SF (various) 0+
259Fm 100 159 259.1006(3)# 1.5(3) s SF (various) 3/2+#
260Fm[n 8][n 9] 100 160 260.10281(55)# 4 ms SF (various) 0+

Source: Wikipedia

List of Fermium Compounds 

Fermium chloride (FmCl2) is the most common compound of fermium. Pure fermium metal has not yet been manufactured despite the fact that alloys containing rare-earth metals have already been produced. However, fermium and ytterbium can be compounded. The resulting alloy is assumed to be shiny and silvery-gray in appearance. 

5 Interesting Facts and Explanations

  1. Fermium the eighth synthetic transuranium element that was classified as a member of the actinide series of the periodic system of elements.
  2. Annually, fermium is produced in amounts of less than a millionth of a gram in the entire world. 
  3. The discovery of fermium wasn’t revealed to the public until 1955 due to the Cold War tensions. 
  4. The Cold War is a historical term referring to the rivalry between the United States of America and the (then) Soviet Union which developed after World War II. The hostility between these two countries arose as a result of the competition between them to become the ‘super-state’, i.e. the world’s leading military power. 
  5. This highly radioactive substance is the element with the highest atomic number that can be produced in a nuclear reactor.