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101Mendelevium

Mendelevium is an actinoid in period 7, in the actinoid series. It has only ever been made a few atoms at a time, so nobody has seen it as a solid, liquid or gas.

Md
Shells: 2, 8, 18, 32, 31, 8, 2. A simple picture: electrons do not move in circles.
Symbol
Md
Atomic number
101 protons in the nucleus
Standard atomic weight
None. Mendelevium has no stable isotopes, so the mass of a sample depends on which isotopes it holds.
Electron configuration
[Rn] 5f13 7s2
Electrons in each shell
2, 8, 18, 32, 31, 8, 2
Group, period, block
–, 7, f
Family
Actinoids
State at 25 °C
not known
Electronegativity
1.3 (Pauling scale)
First ionisation energy
634.9 kJ/mol (6.58 eV) (estimated by NIST)
Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.