Mendelevium
Mendelevium is a synthetic element with chemical symbol Md (formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the antepenultimate actinide and the ninth transuranic element.
Identity
- Atomic mass
- [258] u
- Category
- Actinides
- Group
- 3
- Period
- 7
- Block
- f
- Oxidation States
- +2, +3
- Phase (25 °C)
- Solid
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f13
- Short configuration
- [Rn] 5f13 7s2
- Electrons per shell
- 2, 8, 18, 32, 31, 8, 2
- Electronegativity (Pauling)
- 1.30
- Electron affinity
- 93.9 kJ/mol
- 1st ionization energy
- 635 kJ/mol
Physical properties
- Melting point
- 826.9 °C (1100 K)
- Boiling point
- —
- Density
- —
- Molar heat capacity
- —
Chemical behavior of mendelevium
Mendelevium has thirteen outer electrons ([Rn] 5f¹³ 7s²) and acts as +3, with a notably stable +2 for an actinide, resulting from the stability of the nearly full 5f¹³ shell. Its electronegativity is low (1.30). It is the first element that cannot be produced by neutron capture: it is only known in aqueous solution, as a 'solution element', where its redox potentials have been measured with single-atom techniques.
Reactivity
²⁵⁶Md⁺² + e⁻ → ²⁵⁶Md⁺³
In solution the +2 and +3 states interconvert; the ease of this transfer allowed measuring the standard potential of the Md³⁺/Md²⁺ pair with a single atom.
²⁵⁶Md⁺² → ²⁵⁶Fm + α
Md-256 decays by alpha particle emission with a half-life of 1.17 hours, leaving fermium: the reaction that confirmed its discovery.
²⁵³Es + ⁴He → ²⁵⁶Md + n
The first mendelevium atoms were obtained by bombarding einsteinium with alpha particles in Berkeley's cyclotron.
²⁵⁵Es → ²⁵⁵Md + β
Es-255 beta decay produces Md-255 (27 minutes), another route to obtain mendelevium in traces.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Mendelevium chloride | MdCl₃ | Volatility studies in hydrogen stream |
| Mendelevium cyclopentadienide | Md(C₅H₅)₃ | Identification on gas chromatograph adsorbent |
| Md²⁺ solution | Md(aq)²⁺ | Redox potential measurement at single atoms |
| Md³⁺ solution | Md(aq)³⁺ | Usual state in aqueous medium |
| Md-256 target | ²⁵⁶Md | Confirmation of 1955 discovery |
Electron shell distribution
View in the atom builderIsotopes
No mendelevium isotope is stable. Mendelevium-258 (²⁵⁸Md, 51.5 days) is the most stable; mendelevium-256 (²⁵⁶Md, 1.17 hours) is the most produced and the one that confirmed the discovery in 1955. Mendelevium-257 (²⁵⁷Md, 22.7 minutes) served to measure its redox potential with a single atom.
Occurrence and production
It does not exist in nature: all mendelevium is born in accelerators, bombarding einsteinium with alpha particles or fermium beta decays. It is obtained in single atom quantities or, at most, millions of atoms: never in macroscopic quantities.
History and origin of the name
Ghiorso and colleagues identified it in 1955 in Berkeley, bombarding an einsteinium-253 target with alphas: an experiment designed to demonstrate element-by-element synthesis, with a single atom detected. They named it after Dmitri Mendeleev, creator of the periodic table.
Applications and relevance of mendelevium
Uses of the element
Mendelevium has no practical applications: it serves to study chemical trends at the end of actinides and feeds 'island of stability' models.
Uses of its compounds
Its volatile compounds allowed developing single-atom gas chromatography, a technique later applied to rutherfordium and superheavy elements.
Health, safety and environment
Biological role
It has no known biological function and is extremely radiotoxic. Work is done with a single atom or diluted traces in carrier matrices.
Safety
It is handled only in specialized laboratories (Oak Ridge, Dubna, GSI), with single-atom techniques and alpha shielding. It does not exist outside experiments.
Environment
There are no spills: traces are destroyed or fixed in solid matrices treated as radioactive waste.
Frequently asked questions about Mendelevium
Why is mendelevium so hard to study?
Mendelevium has only been produced in quantities of a few atoms or, at most, millions of atoms, never in macroscopic quantities. Its most stable isotope, mendelevium-258, has a half-life of only 51.5 days, and mendelevium-256, easier to produce, lasts barely 1.17 hours. This drastically limits possible experiments and forces working with single-atom techniques.
Why can mendelevium exist in +2 oxidation state?
Unlike most actinides, which prefer the +3 state, mendelevium can form compounds in +2 state. This is due to the particular stability of its 5f¹³ electron configuration, which facilitates losing only two electrons instead of three. This duality makes it interesting for studying chemical trends at the end of the actinide series.
What role does mendelevium play in the island of stability search?
Mendelevium is located near the theoretical region known as the island of stability, where superheavy isotopes with much longer half-lives are predicted to exist. Studying its nuclear properties helps understand how stability and decay rates change when approaching that region. Although mendelevium itself is unstable, its study provides valuable data for nuclear structure theories.
What is the difference between mendelevium and fermium in element synthesis?
Fermium is the last element that can be produced by neutron capture in a reactor, while mendelevium can only be obtained by bombarding einsteinium with alpha particles in an accelerator. Fermium is produced in picogram quantities, and mendelevium in even smaller quantities, of individual atoms. Both mark the transition toward superheavy elements, which require accelerator nuclear fusion techniques.
What is the difference between mendelevium-256 and mendelevium-258?
Mendelevium-256 has a half-life of only 1.17 hours, but can be produced in larger quantities, so it is used in most experiments. Mendelevium-258, with a half-life of 51.5 days, is the most stable isotope but much harder to obtain. Choice depends on the balance between available quantity and study time.
Why is mendelevium considered a solution element?
Mendelevium is known almost exclusively as ions in aqueous solution, where it adopts +2 or +3 oxidation states. It has never been observed as pure metal nor in solid compounds, so its physical properties such as color, density or crystal structure are unknown or only theoretically predicted. This distinguishes it from elements such as einsteinium, of which macroscopic samples have been obtained.
Why is mendelevium named that way?
Mendelevium received its name in honor of Dmitri Mendeleev, creator of one of the first modern periodic tables. The name recognizes his fundamental contribution to the organization of chemical elements and to predicting properties of not yet discovered elements. It is a tribute to Mendeleev's legacy in chemistry.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.