All practice pages/Interatomic theory/Elements
Element 72, a transition metal
A near-identical twin of zirconium that hid inside its ores for over a century, now inside the transistors of computer chips.
Period 6, group 4. The other transition metals are tinted, and every cell opens its own article.
Like other transition metals, hafnium loses its outer s electrons, and often some d electrons as well, to form positive ions, and it can form more than one kind.
Always found with zirconium, about 2% as much, in the mineral zircon. It is separated out when zirconium is refined for nuclear reactors.
Its chemistry is so close to zirconium's that no one noticed it until 1923, when Dirk Coster and George de Hevesy found it with X-ray spectroscopy in Copenhagen, guided by Niels Bohr's theory of the atom. They named it after Hafnia, the Latin name of Copenhagen.
Hafnium oxide replaced silicon dioxide as the insulating layer in computer chip transistors in 2007, letting them shrink further. Hafnium absorbs neutrons strongly, the opposite of zirconium, so it makes control rods for nuclear reactors, including those in submarines. It also strengthens superalloys and tips plasma cutting torches.