Mendelevium
Atomic Data
| Atomic Number | 101 |
| Symbol | Md |
| Atomic Weight | 258 u |
| Density (STP) | N/A |
| Melting Point | 826.85 °C (1100 K) |
| Boiling Point | N/A °C (None K) |
| Electronegativity | 1.3 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f13 6s2 6p6 7s2 |
| Oxidation States | +2, +3 |
| Phase at STP | Solid |
| Category | Actinoid |
| Period / Group | 7 / None |
| CAS Number | 7440-11-1 |
Electron Configuration
[Rn] 5f13 7s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| O | 5 | 5f | 13 | 91 |
| P | 6 | 6s | 2 | 93 |
| P | 6 | 6p | 6 | 99 |
| Q | 7 | 7s | 2 | 101 |
| Total | 101 | 101 | ||
Isotopes of Mendelevium
Mendelevium is monoisotopic: ²⁵⁸Md is its only naturally occurring stable isotope, accounting for 100% of all natural Mendelevium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Mendelevium-258 | ²⁵⁸Md | 101 | 157 | trace | Stable |
Abundance & Occurrence
Mendelevium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Alpha radiation: Mendelevium isotopes are alpha emitters; all are produced in atom-counting quantities in accelerator experiments and require handling in specialised radiochemical glove boxes with sensitive contamination monitoring.
- Extremely short half-lives: The most accessible isotopes (Md-258, t½ = 51.5 days) decay rapidly; any accumulated sample grows its daughter isotopes quickly, complicating radiological characterisation.
- No macroscopic quantities exist: Mendelevium has never been produced in quantities visible to the naked eye; practical hazard is negligible in absolute terms, but specific activity is high enough to require standard radiological precautions.
- Regulatory controls: All work with mendelevium requires nuclear regulatory authority licensing and is conducted under nuclear safeguards and material accountancy requirements.
Mendelevium in the Real World
Real-World Uses
- Actinide chemistry research: Mendelevium (Md-256, Md-258) is studied to determine whether the divalent (Md²⁺) oxidation state becomes the most stable for actinides beyond fermium, mirroring the lanthanide series behaviour, informing the theoretical understanding of the end of the actinide series.
- Named in honour of Mendeleev: Element 101 was named mendelevium in honour of Dmitri Mendeleev, creator of the periodic table; the naming itself is of historical and cultural significance in the periodic table narrative.
- No commercial applications: Only a few atoms of mendelevium are produced per experiment by accelerator bombardment; its properties are studied atom-by-atom and no applications outside fundamental research are feasible.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is mendelevium used for?
Mendelevium has no practical applications. It is produced only in atom-at-a-time quantities in particle accelerators and can only be studied using ultra-sensitive radiochemical techniques. Its primary use is fundamental research into the chemical and nuclear properties of the actinide series, helping to understand how chemistry evolves at the end of the periodic table.
How was mendelevium discovered?
Mendelevium was synthesised in February 1955 by Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson, and Glenn Seaborg at Berkeley. They bombarded a microscopic amount of einsteinium-253 (itself produced in a reactor) with helium ions in the 60-inch cyclotron. Only 17 atoms were produced in total. It was named after Dmitri Mendeleev, the chemist who created the periodic table and predicted the properties of undiscovered elements.
Is mendelevium radioactive?
Yes, all isotopes of mendelevium are radioactive. The longest-lived, Md-258, has a half-life of 51.5 days. The isotope first synthesised, Md-256, has a half-life of only 77 minutes. All mendelevium isotopes are produced one or a few atoms at a time and decay quickly, making experiments extremely challenging.
How did scientists detect just 17 atoms of mendelevium?
The original mendelevium experiment used a clever chemical technique: after bombardment, the einsteinium target was dissolved and the products were separated by ion exchange chromatography. The tiny amount of mendelevium produced was carried on an ion exchange resin column and eluted in a predictable position based on its expected ionic size (consistent with being a trivalent actinide). The individual mendelevium atoms were then detected by their alpha decay, which produces a characteristic energy signature measurable by a nuclear detector.