72
Hf
Hafnium
178
Hafnium (Hf)
Transition MetalGroup 4Period 6d-block-block
Hafnium is a chemical element with symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, making it the penultimate stable element to be discovered (rhenium was identified two years later).
Latin name: Hafnium
Atomic Number
72
Atomic Mass
178 g/mol
Phase (STP)
Solid
Electron Config.
[Xe] 4f¹⁴ 5d² 6s²
General
SymbolHf
Atomic Number72
Atomic Mass178 g/mol
CategoryTransition Metal
Group4
Period6
Blockd-block
Electron Configuration[Xe] 4f¹⁴ 5d² 6s²
Valence Electrons4
Coloursteel gray metallic
Appearancesteel gray
CAS NumberCAS7440-58-6
Physical Properties
Phase (STP)Solid
Density13.31 g/cm³
Melting Point2232.85°C · 4051.13°F · 2506.00 K
Boiling Point4602.85°C · 8317.13°F · 4876.00 K
Atomic Properties
Atomic Radius212 pm
Electronegativity1.3 Pauling
Ionization Energy659 kJ/mol
Oxidation States+4, +3, +2
Ion ChargeHf2+/Hf3+/Hf4+
Thermodynamic
Molar Heat25.73 J/(mol·K)
Crystal Structure
Crystal Structurehexagonal close-packed (α)
Mechanical Properties
Mohs Hardness5.5
Nuclear & Hazards
Half-lifestable
Abundance
In Universe0.000005%
In Sun0.000004%
In Earth's Crust0.0002%
Discovery & History
Discovery Year1923
Discovered ByGeorg von Hevesy & Dirk Coster
Country of DiscoveryDenmark
Isotopes of Hafnium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Hf-174 | 0.16% | 2.0 × 10¹⁵ years | α |
| Hf-176 | 5.26% | Stable | — |
| Hf-177 | 18.6% | Stable | — |
| Hf-178 | 27.28% | Stable | — |
| Hf-179 | 13.62% | Stable | — |
| Hf-180 | 35.08% | Stable | — |