#72 / 118
72Hf178.49
Transition Metalssolid at STPD-block

Hafnium

Group: 4Period: 6Standard Atomic Weight: 178.49 u

Why is Hafnium in this position?

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

Group Assignment
Group 4

Belongs to Group 4 because it has 4 valence electrons (5d² 6s²).

Period Assignment
Period 6

Belongs to Period 6 because its outermost electrons occupy n=6.

Orbital Block
D-block

Belongs to the d-block because its differentiating electrons enter the 5d subshell.

Chemical Category
Transition Metals

Classified as a transition metal with exceptional neutron absorption and heat resistance.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 32, 10, 2]

Bohr Atomic Shell Model(2, 8, 18, 32, 10, 2)

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

72 Protons (p⁺)106 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 10Shell O: Electron 2 of 10Shell O: Electron 3 of 10Shell O: Electron 4 of 10Shell O: Electron 5 of 10Shell O: Electron 6 of 10Shell O: Electron 7 of 10Shell O: Electron 8 of 10Shell O: Electron 9 of 10Shell O: Electron 10 of 10PShell P: Electron 1 of 2Shell P: Electron 2 of 2HfZ = 72

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):10 / 50 electrons (20%)
Shell P (n=6):2 / 72 electrons (3%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d² 6s²

Neutral ground state configuration. Valence electrons: 4.

Atomic & Quantum Properties

Electronegativity (Pauling)1.3 Pauling
1st Ionization Energy658.5 kJ/mol
Electron Affinity0 kJ/mol
Atomic Radius (empirical)208 pm
Common Oxidation States+4
Crystal StructureHCP

Physical & Thermal Properties

Density at STP13.31 g/cm³
Melting Point2233 °C (2506 K)
Boiling Point4603 °C (4876 K)
Magnetic OrderingParamagnetic
Discovery Year1923
Discovered ByDirk Coster & George de Hevesy

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Nuclear submarine reactor control rods for neutron capture in extreme naval conditions
  • High-k dielectric gate insulator in computer processor transistors (HfO₂)
  • Plasma cutting torch electrodes (Hafnium withstands severe electric arc erosion)
  • Superalloys for aerospace gas turbine rocket nozzles
Occurrence in Nature

Always occurs naturally locked inside zirconium ores (zircon / ZrSiO₄) at a ~2% concentration.

Etymology & Name Origin

From 'Hafnia', the Latin name for Copenhagen, Denmark, where it was discovered using Bohr's quantum model

Important Chemical Compounds
HfO₂ (Hafnia)
HfCl₄ (Hafnium tetrachloride)
Ta₄HfC₅ (Tantalum hafnium carbide / highest melting compound on Earth)
Interesting Chemical Facts
  • Hafnium and Zirconium are the most identical chemical twins in the periodic table; their atomic radii are virtually indistinguishable (159 vs 160 pm) due to the lanthanide contraction.
  • Tantalum hafnium carbide (Ta₄HfC₅) has the highest melting point of any known substance: an astonishing 4,215 °C (7,619 °F).
  • Hafnium was discovered in Copenhagen directly validating Niels Bohr's quantum orbital theory.
Safety & Handling Note

Hafnium metal is non-toxic and biocompatible; fine hafnium dust is pyrophoric.