Mendelevium (Md)

Radioactive metallic transuranic element. Belongs to the actinoid series. Only known isotope, Md-256 has a half-life of 1.3 hours. First identified by Glenn T. Seaborg, Albert Ghiorso and associates in 1955. Alternative name Unnilunium has been proposed. Named after the 'inventor' of the periodic table, Dmitri Mendeleev.

Atomic Number	101
Atomic Weight	258
Mass Number	244

Group
Period	7
Block	f

Protons	101 p⁺
Neutrons	143 n⁰
Electrons	101 e^-

Properties

Energy
Atomic Radius
Molar Volume
Covalent Radius	173 pm 139 pm
Metallic Radius
Ionic Radius	109.5 pm
Crystal Radius	123.5 pm
Van der Waals Radius	246 pm 327.4 pm
Density	10.3 g/cm³
Proton Affinity
Electron Affinity
Ionization Energy	6.58 eV/particle 10 eV/particle 24.3 eV/particle 40 eV/particle 54.1 eV/particle 76 eV/particle 96 eV/particle 115.1 eV/particle 143.9 eV/particle 162 eV/particle 187 eV/particle 215 eV/particle 240 eV/particle 260 eV/particle 282 eV/particle 307 eV/particle 334 eV/particle 360 eV/particle 386 eV/particle 412 eV/particle 438 eV/particle 462 eV/particle 486 eV/particle 659 eV/particle 690 eV/particle 723 eV/particle 760 eV/particle 794 eV/particle 828 eV/particle 885 eV/particle 920 eV/particle 958 eV/particle 994 eV/particle 1,160 eV/particle 1,200 eV/particle 1,250 eV/particle 1,290 eV/particle 1,430 eV/particle 1,480 eV/particle 1,620 eV/particle 1,660 eV/particle 1,840 eV/particle 1,930 eV/particle 2,020 eV/particle 2,110 eV/particle 2,200 eV/particle 2,290 eV/particle 2,380 eV/particle 2,000 eV/particle 2,580 eV/particle 2,680 eV/particle 2,760 eV/particle 2,860 eV/particle 2,950 eV/particle 3,050 eV/particle 3,513 eV/particle 3,592 eV/particle 3,675 eV/particle 3,762 eV/particle 3,845 eV/particle 3,926 eV/particle 4,109 eV/particle 4,194 eV/particle 4,286 eV/particle 4,371 eV/particle 4,720 eV/particle 4,800 eV/particle 4,890 eV/particle 4,970 eV/particle 5,580 eV/particle 5,680 eV/particle 5,930 eV/particle 6,030 eV/particle 9,430 eV/particle 9,620 eV/particle 9,810 eV/particle 10,020 eV/particle 10,220 eV/particle 10,410 eV/particle 10,930 eV/particle 11,130 eV/particle 11,360 eV/particle 11,560 eV/particle 12,140 eV/particle 12,310 eV/particle 12,500 eV/particle 12,680 eV/particle 14,560 eV/particle 14,800 eV/particle 15,200 eV/particle 15,400 eV/particle 31,000 eV/particle 31,500 eV/particle 32,000 eV/particle 32,500 eV/particle 39,500 eV/particle 40,100 eV/particle 41,000 eV/particle 41,548 eV/particle 164,764 eV/particle

Heat of Vaporization
Heat of Fusion
Heat of Formation
Electrons
Electron Shells	2, 8, 18, 32, 31, 8, 2

Valence Electrons	2

Electron Configuration	[Rn] 5f¹³ 7s²

Oxidation States	2, 3
Electronegativity	0.23542
Electrophilicity
Phases
Phase	Solid
Gas Phase
Boiling Point
Melting Point	1,100.15 K
Critical Pressure
Critical Temperature
Triple Point
Visual
Color	Colorless #ffffff #b30da6 #b30da6
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	45
Mendeleev Number	38
Pettifor Number	36
Geochemical Class
Goldschmidt Class	synthetic
Other
Gas Basicity
Dipole Polarizability	109 ± 20 a₀
C6 Dispersion Coefficient
Allotropes
Neutron Cross Section
Neutron Mass Absorption
Quantum Numbers	2F7/2
Space Group	()

Isotopes of Mendelevium

Stable Isotopes	0
Unstable Isotopes	19
Radioactive Isotopes	19

²⁴⁴Md

Abundance	Radioactive ☢️
Relative Atomic Mass	244.081157 ± 0.000402 Da
Mass Number	244
G-Factor
Half Life	0.36 ± 0.14 s
Spin	3
Quadrupole Moment
Discovery Year	2020
Parity	+

²⁴⁴Md Decay Modes

Decay Mode	Intensity
α (α emission)	100%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%
β⁺ SF (β⁺-delayed fission)	14%

²⁴⁵Md

Abundance	Radioactive ☢️
Relative Atomic Mass	245.080864 ± 0.000279 Da
Mass Number	245
G-Factor
Half Life	0.38 ± 0.1 s
Spin	7/2
Quadrupole Moment
Discovery Year	1996
Parity	-

²⁴⁵Md Decay Modes

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

²⁴⁶Md

Abundance	Radioactive ☢️
Relative Atomic Mass	246.081713 ± 0.000279 Da
Mass Number	246
G-Factor
Half Life	0.92 ± 0.18 s
Spin	1
Quadrupole Moment
Discovery Year	1996
Parity	-

²⁴⁶Md Decay Modes

Decay Mode	Intensity
α (α emission)	100%

²⁴⁷Md

Abundance	Radioactive ☢️
Relative Atomic Mass	247.08152 ± 0.000223 Da
Mass Number	247
G-Factor
Half Life	1.19 ± 0.09 s
Spin	7/2
Quadrupole Moment
Discovery Year	1981
Parity	-

²⁴⁷Md Decay Modes

Decay Mode	Intensity
α (α emission)	100%
SF (spontaneous fission)	0.1%

²⁴⁸Md

Abundance	Radioactive ☢️
Relative Atomic Mass	248.082607 ± 0.000198 Da
Mass Number	248
G-Factor
Half Life	7 ± 3 s
Spin
Quadrupole Moment
Discovery Year	1973
Parity

²⁴⁸Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	80%
α (α emission)	20%
β⁺ SF (β⁺-delayed fission)	0.05%

²⁴⁹Md

Abundance	Radioactive ☢️
Relative Atomic Mass	249.082857155 ± 0.000176516 Da
Mass Number	249
G-Factor
Half Life	25.6 ± 0.9 s
Spin	7/2
Quadrupole Moment
Discovery Year	1973
Parity	-

²⁴⁹Md Decay Modes

Decay Mode	Intensity
α (α emission)	75%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%

²⁵⁰Md

Abundance	Radioactive ☢️
Relative Atomic Mass	250.084164934 ± 0.000097606 Da
Mass Number	250
G-Factor
Half Life	54 ± 4 s
Spin	2
Quadrupole Moment
Discovery Year	1973
Parity	-

²⁵⁰Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	93%
α (α emission)	7%
β⁺ SF (β⁺-delayed fission)	0.026%

²⁵¹Md

Abundance	Radioactive ☢️
Relative Atomic Mass	251.084774287 ± 0.00002031 Da
Mass Number	251
G-Factor
Half Life	4.21 ± 0.23 m
Spin	7/2
Quadrupole Moment
Discovery Year	1973
Parity	-

²⁵¹Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	%
α (α emission)	10%

²⁵²Md

Abundance	Radioactive ☢️
Relative Atomic Mass	252.086385 ± 0.000098 Da
Mass Number	252
G-Factor
Half Life	2.3 ± 0.8 m
Spin	1
Quadrupole Moment
Discovery Year	1973
Parity	+

²⁵²Md Decay Modes

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

²⁵³Md

Abundance	Radioactive ☢️
Relative Atomic Mass	253.087143 ± 0.000034 Da
Mass Number	253
G-Factor
Half Life	12 ± 8 m
Spin	7/2
Quadrupole Moment
Discovery Year	1992
Parity	-

²⁵³Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	100%
α (α emission)	0.7%

²⁵⁴Md

Abundance	Radioactive ☢️
Relative Atomic Mass	254.08959 ± 0.000107 Da
Mass Number	254
G-Factor	0
Half Life	10 ± 3 m
Spin	0
Quadrupole Moment	0
Discovery Year	1970
Parity	-

²⁵⁴Md Decay Modes

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

²⁵⁵Md

Abundance	Radioactive ☢️
Relative Atomic Mass	255.091081702 ± 0.000005976 Da
Mass Number	255
G-Factor
Half Life	27 ± 2 m
Spin	7/2
Quadrupole Moment
Discovery Year	1958
Parity	-

²⁵⁵Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	93%
α (α emission)	7%
SF (spontaneous fission)	%

²⁵⁶Md

Abundance	Radioactive ☢️
Relative Atomic Mass	256.093888 ± 0.000133 Da
Mass Number	256
G-Factor
Half Life	77.7 ± 1.8 m
Spin	1
Quadrupole Moment
Discovery Year	1955
Parity	-

²⁵⁶Md Decay Modes

Decay Mode	Intensity
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	90.8%
α (α emission)	9.2%
SF (spontaneous fission)	3%

²⁵⁷Md

Abundance	Radioactive ☢️
Relative Atomic Mass	257.095537343 ± 0.000001683 Da
Mass Number	257
G-Factor
Half Life	5.52 ± 0.05 h
Spin	7/2
Quadrupole Moment
Discovery Year	1965
Parity	-

²⁵⁷Md Decay Modes

Decay Mode	Intensity
ϵ (electron capture)	85%
α (α emission)	15%
SF (spontaneous fission)	%

²⁵⁸Md

Abundance	Radioactive ☢️
Relative Atomic Mass	258.098433634 ± 0.000003729 Da
Mass Number	258
G-Factor
Half Life	51.59 ± 0.29 d
Spin	8
Quadrupole Moment
Discovery Year	1970
Parity	-

²⁵⁸Md Decay Modes

Decay Mode	Intensity
α (α emission)	100%
β⁺ (β⁺ decay; β⁺ = ϵ + e⁺)	0.0015%
β⁻ (β⁻ decay)	0.0015%

²⁵⁹Md

Abundance	Radioactive ☢️
Relative Atomic Mass	259.100445 ± 0.000108 Da
Mass Number	259
G-Factor
Half Life	1.6 ± 0.06 h
Spin	7/2
Quadrupole Moment
Discovery Year	1982
Parity	-

²⁵⁹Md Decay Modes

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

²⁶⁰Md

Abundance	Radioactive ☢️
Relative Atomic Mass	260.10365 ± 0.000339 Da
Mass Number	260
G-Factor
Half Life	27.8 ± 0.8 d
Spin
Quadrupole Moment
Discovery Year	1989
Parity

²⁶⁰Md Decay Modes

Decay Mode	Intensity
SF (spontaneous fission)	100%
α (α emission)	5%
ϵ (electron capture)	5%
β⁻ (β⁻ decay)	3.5%

²⁶¹Md

Abundance	Radioactive ☢️
Relative Atomic Mass	261.105828 ± 0.000546 Da
Mass Number	261
G-Factor
Half Life
Spin	7/2
Quadrupole Moment
Discovery Year
Parity	-

²⁶¹Md Decay Modes

Decay Mode	Intensity
α (α emission)	%

²⁶²Md

Abundance	Radioactive ☢️
Relative Atomic Mass	262.109144 ± 0.000481 Da
Mass Number	262
G-Factor
Half Life
Spin
Quadrupole Moment
Discovery Year
Parity

²⁶²Md Decay Modes

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

History

Mendelevium was discovered by Albert Ghiorso, Glenn T. Seaborg, Gregory R. Choppin, Bernard G. Harvey and Stanley G. Thompson in 1955 at the University of California, Berkeley. It was produced by the bombardment of einsteinium with helium. Mendelevium was identified by chemical analysis in an ion exchange experiment. Named after Dmitri Mendeleev, who created the Periodic Table

Discoverers	G.T.Seaborg, S.G.Tompson, A.Ghiorso, K.Street Jr.
Discovery Location	United States
Discovery Year	1955
Etymology (Name Origin)	Named in honor of the scientist Dmitri Ivanovitch Mendeleyev, who devised the periodic table.
Pronunciation	men-deh-LEE-vi-em (English)

Mendelevium is harmful due to its radioactivity

Mendelevium was the first element to be produced one atom at a time

Uses

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

Sources

Made by bombarding einsteinium with helium ions.

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

Mendelevium on ChemicalAid

Australian Educational Vocabulary ID	scot/3543
CAS Registry Number	7440-11-1
ChEBI ID	33395
ChemSpider ID	22385
DSSTOX compound identifier	DTXCID90147877
DSSTox substance ID	DTXSID90225386
Den Store Danske ID	mendelevium
Elhuyar ZTH ID	028036
Encyclopedia of China Online Database ID (Second Edition)	220827
Encyclopædia Britannica Online ID	science/mendelevium
Encyclopædia Universalis ID	mendelevium
Freebase ID	/m/025s0rf
French Vikidia ID	Mendélévium
GND ID	4169413-2
Gran Enciclopèdia Catalana ID	0122687
Great Russian Encyclopedia Online ID	2204025
InChI	InChI=1S/Md
InChIKey	MQVSLOYRCXQRPM-UHFFFAOYSA-N
Interlingual Index ID	i113965
KBpedia ID	Mendelevium
MeSH descriptor ID	D008573
OmegaWiki Defined Meaning	335094
PubChem CID	23943
Quora topic ID	Mendelevium
Römpp online ID	RD-13-01207
Store norske leksikon ID	mendelevium
Treccani ID	mendelevio
UNII	LW3E571O0Z

Mendelevium (Md)

Properties

Isotopes of Mendelevium

244Md

244Md Decay Modes

245Md

245Md Decay Modes

246Md

246Md Decay Modes

247Md

247Md Decay Modes

248Md

248Md Decay Modes

249Md

249Md Decay Modes

250Md

250Md Decay Modes

251Md

251Md Decay Modes

252Md

252Md Decay Modes

253Md

253Md Decay Modes

254Md

254Md Decay Modes

255Md

255Md Decay Modes

256Md

256Md Decay Modes

257Md

257Md Decay Modes

258Md

258Md Decay Modes

259Md

259Md Decay Modes

260Md

260Md Decay Modes

261Md

261Md Decay Modes

262Md

262Md Decay Modes