Mendelevium

no group (f-block) · period 7 · f-block · actinide

Identity

Name and symbol: Mendelevium, Md
Atomic number: 101 protons
Position: no group (f-block) · period 7 · f-block · actinide
CAS number: 7440-11-1

Atomic structure

Atomic mass: 258 u
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹³
[Rn] 7s²⁵f¹³
Electrons per shell: 2, 8, 18, 32, 31, 8, 2
Valence electrons: 15 ns, (n-1)d and (n-2)f

nuclide	half-life	decay
²⁵⁸Md	51.59 d	α≈100%; β+<0.0015%; β-<0.0015%
²⁶⁰Md	27.8 d	SF≈100%; α<5%; ε<5%; β-<3.5%
²⁵⁷Md	5.52 h	ε=85±0.3%; α=15±0.3%; SF ?
²⁵⁶Mdm	100 m [Estimated]	β+ ?; α ?; SF ?

no stable isotope; the longest-lived nuclides

Physical properties

State at room temperature: Solid
Melting point: 1,100 K (826.85 °C)
Boiling point: not in sources
Density: not in sources
Appearance: not in sources
Thermal conductivity: not in sources
Electrical resistivity: not in sources
Electrical conductivity: not in sources
Crystal structure: face-centered cubic
Molar heat capacity: not in sources

Chemical properties

Oxidation states: +3, +2
Electronegativity: 1.3 (Pauling Scale)
Ionisation energy: 6.58 eV
1st 635 kJ/mol
Electron affinity: not in sources
Atomic radius: not in sources
Ionic radius: not in sources

Reactivity: Known only in tracer solution work; no pure compound has been made. It is a trivalent actinide in aqueous solution, with a moderately stable +2 state reached under reducing conditions and an unconfirmed +1 state.
with water: Not known for the metal; in solution Md3+ is the normal ion and Md2+ is stable in water in the absence of oxidants.
with oxygen, air: Not known.
with acids: In acid solution behaves as a trivalent actinide, eluting just after fermium from cation-exchange resin and coprecipitating as insoluble hydroxide and fluoride with trivalent lanthanides.
with halogens: Not known; no mendelevium halide has been prepared.

Typical compounds: not in sources

Occurrence, production and use

Crustal abundance: Not Applicable
Oceanic abundance: Not Applicable

Occurrence and sources

synthetic only made by bombarding einsteinium with alpha particles

Extraction, production: 253Es (4He, n) 256Md and 253Es (4He, 2n) 255Md
nuclear reactions as printed by PubChem

Uses

Since only small amounts of mendelevium have ever been produced, it currently has no uses outside of basic scientific research.

256Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution.

Safety, toxicity: not in sources

Discovery and name

Discovered by: Lawrence Berkeley National Laboratory
Discovered: 1955
First isolated: not in sources
Named by: not in sources
Origin of the name: after Dmitri Mendeleev

Mendelevium does not occur naturally in the Earth’s crust. It was first synthesized in 1955 by Glenn T. Seaborg and his team at the University of California using the reactions 253Es (4He, n) 256Md and 253Es (4He, 2n) 255Md. Mendelevium is named for the Russian scientist, Dmitri Mendeleev (Fig. IUPAC.101.1), who developed the Periodic Table of the chemical elements [636], [637]. There are no applications for isotopes of mendelevium aside from scientific research.

Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of the actinide elements.

Conventions

Valence electrons are counted by the usual convention: the outer shell for s- and p-block elements, ns and (n-1)d for the d-block, ns, (n-1)d and (n-2)f for the f-block. Lanthanides and actinides are placed in the f-block with no group number. Electrical conductivity is the reciprocal of the printed resistivity. Ionic radii are Shannon effective radii, six-coordinate unless noted. Where a field reads “not in sources” the value was not found; it is a gap, not a zero. Regulatory limits are the published values and change often, so check the standard in force at your site and the numbers written into your own permit before you design to them.

Data

Element records, isotopes, radii and the descriptive text come from PubChem (NCBI), the Los Alamos National Laboratory periodic table, IUPAC CIAAW and the IAEA Atomic Mass Data Center. Appearance, thermal conductivity, electrical resistivity, crystal structure, discovery and the origin of each name come from Wikipedia and Periodic-Table-JSON, used under CC BY-SA 4.0. Hazard classifications come from the ECHA C&L inventory via PubChem. Ionic radii follow R. D. Shannon (1976). The water chapters cite their own sources at the foot of each entry, and are written to the level of Snoeyink and Jenkins, Stumm and Morgan, MWH's Water Treatment and Metcalf and Eddy.