Fermium (Fm)

Radioactive metallic transuranic element, belongs to the actinoids. Ten known isotopes, most stable is Fm-257 with a half-life of 10 days. First identified by Albert Ghiorso and associates in the debris of the first hydrogen-bomb explosion in 1952.

Atomic Number	100
Atomic Weight	257
Mass Number	241

Group
Period	7
Block	f

Protons	100 p⁺
Neutrons	141 n⁰
Electrons	100 e^-

Properties

Energy
Atomic Radius
Molar Volume
Covalent Radius	167 pm
Metallic Radius
Ionic Radius	110.5 pm
Crystal Radius	124.5 pm
Van der Waals Radius	245 pm 328.6 pm
Density	9.7 g/cm³
Proton Affinity
Electron Affinity
Ionization Energy	6.5 eV/particle 10 eV/particle 23.2 eV/particle 39.3 eV/particle 55 eV/particle 74 eV/particle 93 eV/particle 120 eV/particle 136 eV/particle 162 eV/particle 185 eV/particle 209 eV/particle 237 eV/particle 257 eV/particle 276 eV/particle 300 eV/particle 326 eV/particle 351 eV/particle 377 eV/particle 402 eV/particle 430 eV/particle 453 eV/particle 616 eV/particle 647 eV/particle 680 eV/particle 716 eV/particle 749 eV/particle 782 eV/particle 837 eV/particle 871 eV/particle 909 eV/particle 944 eV/particle 1,110 eV/particle 1,150 eV/particle 1,190 eV/particle 1,230 eV/particle 1,370 eV/particle 1,420 eV/particle 1,550 eV/particle 1,600 eV/particle 1,770 eV/particle 1,860 eV/particle 1,940 eV/particle 2,030 eV/particle 2,120 eV/particle 2,210 eV/particle 2,300 eV/particle 2,390 eV/particle 2,490 eV/particle 2,590 eV/particle 2,680 eV/particle 2,760 eV/particle 2,900 eV/particle 2,950 eV/particle 3,403 eV/particle 3,480 eV/particle 3,561 eV/particle 3,647 eV/particle 3,730 eV/particle 3,810 eV/particle 3,986 eV/particle 4,070 eV/particle 4,160 eV/particle 4,245 eV/particle 4,586 eV/particle 4,670 eV/particle 4,760 eV/particle 4,840 eV/particle 5,420 eV/particle 5,510 eV/particle 5,760 eV/particle 5,860 eV/particle 9,200 eV/particle 9,370 eV/particle 9,570 eV/particle 9,770 eV/particle 9,970 eV/particle 10,160 eV/particle 10,660 eV/particle 10,860 eV/particle 11,080 eV/particle 11,280 eV/particle 11,850 eV/particle 12,020 eV/particle 12,220 eV/particle 12,390 eV/particle 14,180 eV/particle 14,400 eV/particle 14,800 eV/particle 15,000 eV/particle 30,300 eV/particle 30,800 eV/particle 31,300 eV/particle 31,800 eV/particle 38,400 eV/particle 39,100 eV/particle 40,000 eV/particle 40,482.2 eV/particle 158,152.5 eV/particle 160,804 eV/particle

Heat of Vaporization
Heat of Fusion
Heat of Formation
Electrons
Electron Shells	2, 8, 18, 32, 30, 8, 2

Valence Electrons	2

Electron Configuration	[Rn] 5f¹² 7s²

Oxidation States	2, 3
Electronegativity	0.22485
Electrophilicity
Phases
Phase	Solid
Gas Phase
Boiling Point
Melting Point	1,800.15 K
Critical Pressure
Critical Temperature
Triple Point
Visual
Color	Colorless #ffffff #b31fba #b31fba
Appearance
Refractive Index
Thermodynamic Properties
Thermal Conductivity
Thermal Expansion
Molar Heat Capacity
Specific Heat Capacity
Heat Capacity Ratio (Adiabatic Index)
Electrical Properties
Type
Electrical Conductivity
Electrical Resistivity
Superconducting Point
Magnetism
Type
Magnetic Susceptibility (Mass)
Magnetic Susceptibility (Molar)
Magnetic Susceptibility (Volume)
Magnetic Ordering
Curie Point
Neel Point
Structure
Crystal Structure	()
Lattice Constant
Lattice Angles
Mechanical Properties
Hardness
Bulk Modulus
Shear Modulus
Young Modulus
Poisson Ratio
Speed of Sound
Classification
Category	Actinides, Actinides
CAS Group
IUPAC Group
Glawe Number	44
Mendeleev Number	36
Pettifor Number	37
Geochemical Class
Goldschmidt Class	synthetic
Other
Gas Basicity
Dipole Polarizability	113 ± 20 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section	5,800
Neutron Mass Absorption
Quantum Numbers	3H6
Space Group	()

Isotopes of Fermium

Stable Isotopes	0
Unstable Isotopes	20
Radioactive Isotopes	20

²⁴¹Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	241.074311 ± 0.000322 Da
Mass Number	241
G-Factor
Half Life	730 ± 60 us
Spin	5/2
Quadrupole Moment
Discovery Year	2008
Parity	+

²⁴¹Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	%
α (α emission)	14%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	12%

²⁴²Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	242.07343 ± 0.00043 Da
Mass Number	242
G-Factor	0
Half Life	800 ± 200 us
Spin	0
Quadrupole Moment	0
Discovery Year	1975
Parity	+

²⁴²Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	100%
α (α emission)	%

²⁴³Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	243.074414 ± 0.00014 Da
Mass Number	243
G-Factor
Half Life	231 ± 9 ms
Spin	7/2
Quadrupole Moment
Discovery Year	1981
Parity	-

²⁴³Fm Decay Modes

Decay Mode	Intensity
α (α emission)	91%
SF (spontaneous fission)	9%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%

²⁴⁴Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	244.074036 ± 0.000216 Da
Mass Number	244
G-Factor	0
Half Life	3.12 ± 0.08 ms
Spin	0
Quadrupole Moment	0
Discovery Year	1967
Parity	+

²⁴⁴Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	97%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	2%
α (α emission)	1%

²⁴⁵Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	245.075354 ± 0.00021 Da
Mass Number	245
G-Factor
Half Life	4.2 ± 1.3 s
Spin	1/2
Quadrupole Moment	0
Discovery Year	1967
Parity	+

²⁴⁵Fm Decay Modes

Decay Mode	Intensity
α (α emission)	100%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	7%
SF (spontaneous fission)	0.3%

²⁴⁶Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	246.075353334 ± 0.000014675 Da
Mass Number	246
G-Factor	0
Half Life	1.54 ± 0.04 s
Spin	0
Quadrupole Moment	0
Discovery Year	1966
Parity	+

²⁴⁶Fm Decay Modes

Decay Mode	Intensity
α (α emission)	93.2%
SF (spontaneous fission)	6.8%
ϵ (electron capture)	1.3%

²⁴⁷Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	247.076944 ± 0.000194 Da
Mass Number	247
G-Factor
Half Life	31 ± 1 s
Spin	7/2
Quadrupole Moment
Discovery Year	1967
Parity	+

²⁴⁷Fm Decay Modes

Decay Mode	Intensity
α (α emission)	64%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%

²⁴⁸Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	248.077185451 ± 0.000009122 Da
Mass Number	248
G-Factor	0
Half Life	34.5 ± 1.2 s
Spin	0
Quadrupole Moment	0
Discovery Year	1958
Parity	+

²⁴⁸Fm Decay Modes

Decay Mode	Intensity
α (α emission)	100%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%
SF (spontaneous fission)	0.1%

²⁴⁹Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	249.078926042 ± 0.000006668 Da
Mass Number	249
G-Factor
Half Life	1.6 ± 0.1 m
Spin	7/2
Quadrupole Moment
Discovery Year	1960
Parity	+

²⁴⁹Fm Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%
α (α emission)	33%

²⁵⁰Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	250.079519765 ± 0.000008468 Da
Mass Number	250
G-Factor	0
Half Life	31 ± 1.1 m
Spin	0
Quadrupole Moment	0
Discovery Year	1954
Parity	+

²⁵⁰Fm Decay Modes

Decay Mode	Intensity
α (α emission)	100%
SF (spontaneous fission)	0.0069%
ϵ (electron capture)	%

²⁵¹Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	251.08154513 ± 0.000015342 Da
Mass Number	251
G-Factor
Half Life	5.3 ± 0.08 h
Spin	9/2
Quadrupole Moment
Discovery Year	1957
Parity	-

²⁵¹Fm Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	98.2%
α (α emission)	1.8%

²⁵²Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	252.082466019 ± 0.000005604 Da
Mass Number	252
G-Factor	0
Half Life	25.39 ± 0.04 h
Spin	0
Quadrupole Moment	0
Discovery Year	1956
Parity	+

²⁵²Fm Decay Modes

Decay Mode	Intensity
α (α emission)	100%
SF (spontaneous fission)	0.0023%
2β⁺ (double β⁺ decay)	%

²⁵³Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	253.085180945 ± 0.000001662 Da
Mass Number	253
G-Factor
Half Life	3 ± 0.12 d
Spin	1/2
Quadrupole Moment	0
Discovery Year	1957
Parity	+

²⁵³Fm Decay Modes

Decay Mode	Intensity
ϵ (electron capture)	88%
α (α emission)	12%

²⁵⁴Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	254.086852424 ± 0.000001978 Da
Mass Number	254
G-Factor	0
Half Life	3.24 ± 0.002 h
Spin	0
Quadrupole Moment	0
Discovery Year	1954
Parity	+

²⁵⁴Fm Decay Modes

Decay Mode	Intensity
α (α emission)	99.9408%
SF (spontaneous fission)	0.0592%

²⁵⁵Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	255.089963495 ± 0.000004223 Da
Mass Number	255
G-Factor
Half Life	20.07 ± 0.07 h
Spin	7/2
Quadrupole Moment
Discovery Year	1954
Parity	+

²⁵⁵Fm Decay Modes

Decay Mode	Intensity
α (α emission)	100%
SF (spontaneous fission)	2.4%

²⁵⁶Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	256.091771699 ± 0.000003241 Da
Mass Number	256
G-Factor	0
Half Life	157.1 ± 1.3 m
Spin	0
Quadrupole Moment	0
Discovery Year	1955
Parity	+

²⁵⁶Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	91.9%
α (α emission)	8.1%

²⁵⁷Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	257.095105419 ± 0.000004669 Da
Mass Number	257
G-Factor
Half Life	100.5 ± 0.2 d
Spin	9/2
Quadrupole Moment
Discovery Year	1964
Parity	+

²⁵⁷Fm Decay Modes

Decay Mode	Intensity
α (α emission)	99.79%
SF (spontaneous fission)	0.21%

²⁵⁸Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	258.097077 ± 0.000215 Da
Mass Number	258
G-Factor	0
Half Life	370 ± 14 us
Spin	0
Quadrupole Moment	0
Discovery Year	1971
Parity	+

²⁵⁸Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	100%
α (α emission)	%

²⁵⁹Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	259.100596 ± 0.000304 Da
Mass Number	259
G-Factor
Half Life	1.5 ± 0.2 s
Spin
Quadrupole Moment
Discovery Year	1980
Parity

²⁵⁹Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	100%

²⁶⁰Fm

Abundance	Radioactive ☢️
Relative Atomic Mass	260.102809 ± 0.000467 Da
Mass Number	260
G-Factor	0
Half Life
Spin	0
Quadrupole Moment	0
Discovery Year
Parity	+

²⁶⁰Fm Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	%

History

Fermium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952. It was identified by Albert Ghiorso and co-workers at the University of California, Berkeley in collaboration with the Argonne and Los Alamos National Laboratories, in the fallout from the Ivy Mike nuclear test. The new element was produced by the nuclear fission of 17 neutrons with uranium-238. Named after Nobel laureate Enrico Fermi, one of the pioneers of nuclear physics

Discoverers	Argonne, Los Alamos, U of Calif
Discovery Location	United States
Discovery Year	1953
Etymology (Name Origin)	Named in honor of the scientist Enrico Fermi.
Pronunciation	FER-mi-em (English)

Fermium is harmful due to its radioactivity

Sixteen isotopes of fermium are known to exist

Uses

Fermium is used for scientific research purposes only. It has no significant commercial applications.

Sources

Produced by bombarding lighter transuranium elements with still lighter particles or by neutron capture.

Abundance
Abundance in Earth's crust
Abundance in Oceans
Abundance in Human Body	0 %
Abundance in Meteor	0 %
Abundance in Sun	0 %
Abundance in Universe	0 %

Nuclear Screening Constants

Fermium on ChemicalAid

Australian Educational Vocabulary ID	scot/3519
CAS Registry Number	7440-72-4
ChEBI ID	33394
ChemSpider ID	22434
DSSTOX compound identifier	DTXCID60147884
DSSTox substance ID	DTXSID60225393
Den Store Danske ID	fermium
Encyclopædia Britannica Online ID	science/fermium
Encyclopædia Universalis ID	fermium
Freebase ID	/m/025rqck
GND ID	4490995-0
Gran Enciclopèdia Catalana ID	0108657
Great Russian Encyclopedia Online ID	4709674
InChI	InChI=1S/Fm
InChIKey	MIORUQGGZCBUGO-UHFFFAOYSA-N
KBpedia ID	Fermium
MeSH descriptor ID	D005286
OmegaWiki Defined Meaning	158627
PubChem CID	23998
Römpp online ID	RD-06-00507
Store norske leksikon ID	fermium
Treccani ID	fermio
UNII	Q70I3KBF4W
WordNet 3.1 Synset ID	14661517-n

Fermium (Fm)

Properties

Isotopes of Fermium

241Fm

241Fm Decay Modes

242Fm

242Fm Decay Modes

243Fm

243Fm Decay Modes

244Fm

244Fm Decay Modes

245Fm

245Fm Decay Modes

246Fm

246Fm Decay Modes

247Fm

247Fm Decay Modes

248Fm

248Fm Decay Modes

249Fm

249Fm Decay Modes

250Fm

250Fm Decay Modes

251Fm

251Fm Decay Modes

252Fm

252Fm Decay Modes

253Fm

253Fm Decay Modes

254Fm

254Fm Decay Modes

255Fm

255Fm Decay Modes

256Fm

256Fm Decay Modes

257Fm

257Fm Decay Modes

258Fm

258Fm Decay Modes

259Fm

259Fm Decay Modes

260Fm

260Fm Decay Modes