Norwegium

Hafnium,  ₇₂Hf

General properties
Pronunciation	/ˈhæfniəm/ HAF-nee-əm
Appearance	steel gray
Standard atomic weight (Ar, std)	7002178490000000000♠178.49(2)
Hafnium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Zr ↑ Hf ↓ Rf lutetium ← hafnium → tantalum
Atomic number (Z)	72
Group, period	group 4, period 6
Block	d-block
Element category	transition metal
Electron configuration	[Xe] 4f14 5d2 6s2
Electrons per shell	2, 8, 18, 32, 10, 2
Physical properties
Phase (at STP)	solid
Melting point	2506 K ​(2233 °C, ​4051 °F)
Boiling point	4876 K ​(4603 °C, ​8317 °F)
Density (near r.t.)	13.31 g/cm3
when liquid (at m.p.)	12 g/cm3
Heat of fusion	27.2 kJ/mol
Heat of vaporization	648 kJ/mol
Molar heat capacity	25.73 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2689 2954 3277 3679 4194 4876
Atomic properties
Oxidation states	4, 3, 2, 1, −2 ​(an amphoteric oxide)
Electronegativity	Pauling scale: 1.3
Ionization energies	1st: 658.5 kJ/mol 2nd: 1440 kJ/mol 3rd: 2250 kJ/mol
Atomic radius	empirical: 159 pm
Covalent radius	175±10 pm
Spectral lines
Miscellanea
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	3010 m/s (at 20 °C)
Thermal expansion	5.9 µm/(m·K) (at 25 °C)
Thermal conductivity	23.0 W/(m·K)
Electrical resistivity	331 nΩ·m (at 20 °C)
Magnetic ordering	paramagnetic
Magnetic susceptibility	+75.0·10−6 cm3/mol (at 298 K)
Young's modulus	78 GPa
Shear modulus	30 GPa
Bulk modulus	110 GPa
Poisson ratio	0.37
Mohs hardness	5.5
Vickers hardness	1520–2060 MPa
Brinell hardness	1450–2100 MPa
CAS Number	7440-58-6
History
Naming	after Hafnia. Latin for: Copenhagen, where it was discovered
Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Dirk Coster and George de Hevesy (1922)
Main isotopes of hafnium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 172Hf syn 1.87 y ε 172Lu 174Hf 0.16% 2×1015 y α 170Yb 176Hf 5.26% stable 177Hf 18.60% stable 178Hf 27.28% stable 178m2Hf syn 31 y IT 178Hf 179Hf 13.62% stable 180Hf 35.08% stable 182Hf syn 8.9×106 y β− 182Ta
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Spectral lines

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 many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Dr Alexander Scott, making it the last stable element to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.

Hafnium is used in filaments and electrodes. Some semiconductor fabrication processes use its oxide for integrated circuits at 45 nm and smaller feature lengths. Some superalloys used for special applications contain hafnium in combination with niobium, titanium, or tungsten.

Hafnium's large neutron capture cross-section makes it a good material for neutron absorption in control rods in nuclear power plants, but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors.

Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium (due to its having the same number of valence electrons, being in the same group, but also to relativistic effects; the expected expansion of atomic radii from period 5 to 6 is almost exactly cancelled out by the lanthanide contraction). The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity.