Mendelevium (Md)
Element 101 · Actinide · atomic mass [258] u · f-block, period 7
Electron shells: 2, 8, 18, 32, 31, 8, 2
Mendelevium was the first element made one atom at a time, produced by bombarding einsteinium with helium nuclei. Only about 17 atoms existed in the original experiment.
The team detected the very first mendelevium atoms one by one, as individual decay clicks.
- Atomic number
- 101
- Atomic mass
- [258] u
- Electron configuration
- [Rn] 7s² 5f¹³
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +2, +3
- Electronegativity
- 1.3 (Pauling)
- Melting point
- 827 °C
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Solid
- Appearance
- Unknown; presumed metallic
- Discovered
- Albert Ghiorso, Glenn T. Seaborg and colleagues, 1955
101 protons, and 101 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Shown in the strip below the table
What Mendelevium is used for
- Scientific research only
Atomic structure of Mendelevium
A neutral mendelevium atom has 101 protons and 101 electrons. Its most common isotope carries about 157 neutrons, which is where the mass number 258 comes from. Change the neutron count and you have a different isotope of mendelevium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 31, 8, 2. In orbital notation that is [Rn] 7s² 5f¹³. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Mendelevium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Mendelevium sits in the periodic table
Discovery and naming
Mendelevium was discovered by Albert Ghiorso, Glenn T. Seaborg and colleagues in 1955. Its name comes from Dmitri Mendeleev, which is also why its symbol (Md) does not match its English name.
Every isotope of mendelevium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Mendelevium?
Mendelevium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 258 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Mendelevium have?
Mendelevium has 101 protons, because the atomic number is the proton count and that is what makes an atom Mendelevium at all. A neutral Mendelevium atom has the same number of electrons, 101. The neutron count varies by isotope; the most common one has about 157, since 258 − 101 = 157.
What is the electron configuration of Mendelevium?
The electron configuration of Mendelevium is [Rn] 7s² 5f¹³. Its electrons are arranged 2, 8, 18, 32, 31, 8, 2 across 7 shells.
Is Mendelevium a metal?
Yes. Mendelevium is classified as a actinide, on the metallic side of the table.
What group and period is Mendelevium in?
Mendelevium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Mendelevium?
Mendelevium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound. Across all its compounds it shows oxidation states of +2, +3.
What is the melting point of Mendelevium?
Mendelevium melts at 827 °C. That puts it in the solids at everyday temperatures.
What is Mendelevium used for?
Scientific research only. Mendelevium was the first element made one atom at a time, produced by bombarding einsteinium with helium nuclei.
Who discovered Mendelevium, and where does its name come from?
Mendelevium (Md) was discovered by Albert Ghiorso, Glenn T. Seaborg and colleagues in 1955. The name comes from Dmitri Mendeleev.
Is Mendelevium radioactive?
Yes. Every isotope of Mendelevium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.