Symbol	Hf
Atomic number	72
Group	4 (Titanium group)
Period	6
Block	d
Classification	Transition Metal

Appearance	Steel gray
Color	Gray

Number of protons	72 p+
Number of neutrons	106 n0
Number of electrons	72 e-

From Wikipedia, the free encyclopediaHafnium 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).

Phase at STP	Solid
Density	13.31 g/cm3
Atomic weight	178.492 u

Melting point	2506 K 2232.85 °C 4051.13 °F
Boiling point	4876 K 4602.85 °C 8317.13 °F
Heat of vaporization	661.07 kJ/mol

Electronegativity (Pauling Scale)	1.3
Electron affinity	17.18 kJ/mol
Oxidation states	−2, 0, +1, +2, +3, +4 (an amphoteric oxide)
Ionization energies	658.5 kJ/mol 1440 kJ/mol 2250 kJ/mol 3216 kJ/mol

Electron configuration Shorthand configuration	[Xe] 4f14 5d2 6s2
Electron configuration Full configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d2 6s2
Electron configuration chart	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d2 6s2
Electrons per shell	2, 8, 18, 32, 10, 2
Valence electrons	2
Valency electrons	4
Bohr model	Figure: Shell diagram of Hafnium (Hf) atom.
Orbital Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 6s

Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Dirk Coster, George de Hevesy (1922)
Discovery of hafnium In his report on The Periodic Law of the Chemical Elements, in 1869, Dmitri Mendeleev had implicitly predicted the existence of a heavier analog of titanium and zirconium. The X-ray spectroscopy done by Henry Moseley in 1914 showed a direct dependency between spectral line and effective nuclear charge. This led to the nuclear charge, or atomic number of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of lanthanides and showed the gaps in the atomic number sequence at numbers 43, 61, 72, and 75. The discovery of the gaps led to an extensive search for the missing elements. And the reappearance in 1922 of Urbain's claims that element 72 was a rare earth element discovered in 1911, Dirk Coster and Georg von Hevesy were motivated to search for the new element in zirconium ores.Hafnium was discovered by the two in 1923 in Copenhagen, Denmark, validating the original 1869 prediction of Mendeleev. It was ultimately found in zircon in Norway through X-ray spectroscopy analysis. The place where the discovery took place led to the element being named for the Latin name for "Copenhagen", Hafnia, the home town of Niels Bohr.

CAS Number	7440-58-6
ChemSpider ID	22422
EC number	231-166-4
PubChem CID Number	23986