#101 / 118
101Md[258]
Actinidessolid at STPF-block

Mendelevium

Group: f-block•Period: 7•Standard Atomic Weight: [258] u
Open Full Periodic TableView Bohr Model

Why is Mendelevium in this position?

Understanding the scientific rationale behind Mendelevium's position in the periodic table:

Group Assignment
Group Lanthanide / Actinide

Actinide series element filling the 5f subshell.

Period Assignment
Period 7

Belongs to Period 7 because its outermost electrons occupy n=7.

Orbital Block
F-block

Belongs to the f-block because valence electrons fill 5f orbitals (5f¹³ 7s²).

Chemical Category
Actinides

Classified as an actinide synthetic radioactive metal.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 32, 31, 8, 2]

Bohr Atomic Shell Model(2, 8, 18, 32, 31, 8, 2)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

101 Protons (p⁺)157 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 18Shell M: Electron 2 of 18Shell M: Electron 3 of 18Shell M: Electron 4 of 18Shell M: Electron 5 of 18Shell M: Electron 6 of 18Shell M: Electron 7 of 18Shell M: Electron 8 of 18Shell M: Electron 9 of 18Shell M: Electron 10 of 18Shell M: Electron 11 of 18Shell M: Electron 12 of 18Shell M: Electron 13 of 18Shell M: Electron 14 of 18Shell M: Electron 15 of 18Shell M: Electron 16 of 18Shell M: Electron 17 of 18Shell M: Electron 18 of 18NShell N: Electron 1 of 32Shell N: Electron 2 of 32Shell N: Electron 3 of 32Shell N: Electron 4 of 32Shell N: Electron 5 of 32Shell N: Electron 6 of 32Shell N: Electron 7 of 32Shell N: Electron 8 of 32Shell N: Electron 9 of 32Shell N: Electron 10 of 32Shell N: Electron 11 of 32Shell N: Electron 12 of 32Shell N: Electron 13 of 32Shell N: Electron 14 of 32Shell N: Electron 15 of 32Shell N: Electron 16 of 32Shell N: Electron 17 of 32Shell N: Electron 18 of 32Shell N: Electron 19 of 32Shell N: Electron 20 of 32Shell N: Electron 21 of 32Shell N: Electron 22 of 32Shell N: Electron 23 of 32Shell N: Electron 24 of 32Shell N: Electron 25 of 32Shell N: Electron 26 of 32Shell N: Electron 27 of 32Shell N: Electron 28 of 32Shell N: Electron 29 of 32Shell N: Electron 30 of 32Shell N: Electron 31 of 32Shell N: Electron 32 of 32OShell O: Electron 1 of 31Shell O: Electron 2 of 31Shell O: Electron 3 of 31Shell O: Electron 4 of 31Shell O: Electron 5 of 31Shell O: Electron 6 of 31Shell O: Electron 7 of 31Shell O: Electron 8 of 31Shell O: Electron 9 of 31Shell O: Electron 10 of 31Shell O: Electron 11 of 31Shell O: Electron 12 of 31Shell O: Electron 13 of 31Shell O: Electron 14 of 31Shell O: Electron 15 of 31Shell O: Electron 16 of 31Shell O: Electron 17 of 31Shell O: Electron 18 of 31Shell O: Electron 19 of 31Shell O: Electron 20 of 31Shell O: Electron 21 of 31Shell O: Electron 22 of 31Shell O: Electron 23 of 31Shell O: Electron 24 of 31Shell O: Electron 25 of 31Shell O: Electron 26 of 31Shell O: Electron 27 of 31Shell O: Electron 28 of 31Shell O: Electron 29 of 31Shell O: Electron 30 of 31Shell O: Electron 31 of 31PShell P: Electron 1 of 8Shell P: Electron 2 of 8Shell P: Electron 3 of 8Shell P: Electron 4 of 8Shell P: Electron 5 of 8Shell P: Electron 6 of 8Shell P: Electron 7 of 8Shell P: Electron 8 of 8QShell Q: Electron 1 of 2Shell Q: Electron 2 of 2MdZ = 101

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):18 / 18 electrons (100%)
Shell N (n=4):32 / 32 electrons (100%)
Shell O (n=5):31 / 50 electrons (62%)
Shell P (n=6):8 / 72 electrons (11%)
Shell Q (n=7):2 / 98 electrons (2%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹³ 6s² 6p⁶ 7s²

Neutral ground state configuration. Valence electrons: 15.

Atomic & Quantum Properties

Electronegativity (Pauling)1.3 Pauling
1st Ionization Energy635 kJ/mol
Electron Affinity-42 kJ/mol
Atomic Radius (empirical)165 pm
Common Oxidation States+3, +2
Crystal StructureFCC

Physical & Thermal Properties

Density at STP10.3 g/cm³ (estimated)
Melting Point827 °C (1100 K)
Boiling Point1100 °C (1373 K)
Magnetic OrderingParamagnetic
Discovery Year1955
Discovered ByAlbert Ghiorso, Bernard G. Harvey, Gregory R. Choppin, Stanley G. Thompson & Glenn T. Seaborg

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Pure scientific research investigating anomalous +2 oxidation states in heavy actinides
Occurrence in Nature

Synthesized atom-by-atom in particle accelerators by bombarding Einsteinium-253 with alpha particles.

Etymology & Name Origin

Named in honor of Dmitri Mendeleev, the father of the periodic table

Important Chemical Compounds
MdCl₂ (Mendelevium dichloride)
MdCl₃ (Mendelevium trichloride)
Interesting Chemical Facts
  • • Mendelevium was the very first chemical element in history to be produced and identified 'one atom at a time'.
  • • Glenn Seaborg named element 101 after Russian chemist Dmitri Mendeleev at the height of the Cold War, a bold gesture of scientific unity that required US State Department approval.
  • • The discovery team wired a counter directly to a loud bell in the UC Berkeley radiation lab that rang every time a single atom of mendelevium was formed.
Safety & Handling Note

Radioactive alpha/fission emitter; produced only in minute atomic quantities.

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