As is typical for early transition metals, zirconium and hafnium have only the group oxidation state of +4 as a major one, and are quite electropositive and have a less rich coordination chemistry.

Their inherent reactivity is completely masked due to the formation of a dense oxide layer that protects them from corrosion, as well as attack by many acids and alkalis.

Rutherfordium is strongly radioactive: it does not occur naturally and must be produced by artificial synthesis, but its observed and theoretically predicted properties are consistent with it being a heavier homologue of hafnium.

Zircon was known as a gemstone from ancient times,[1] but it was not known to contain a new element until the work of German chemist Martin Heinrich Klaproth in 1789.

Cornish chemist Humphry Davy also attempted to isolate this new element in 1808 through electrolysis, but failed: he gave it the name zirconium.

[1] Cornish mineralogist William Gregor first identified titanium in ilmenite sand beside a stream in Cornwall, Great Britain in the year 1791.

In 1795, chemist Martin Heinrich Klaproth independently rediscovered the metal oxide in rutile from the Hungarian village Boinik.

[6] The X-ray spectroscopy done by Henry Moseley in 1914 showed a direct dependency between spectral line and effective nuclear charge.

These suggestions were based on Bohr's theories of the atom, the X-ray spectroscopy of Moseley, and the chemical arguments of Friedrich Paneth.

[18] Hafnium was separated from zirconium through repeated recrystallization of the double ammonium or potassium fluorides by Valdemar Thal Jantzen and von Hevesy.

The first reported detection was by a team at the Joint Institute for Nuclear Research (JINR), which in 1964 claimed to have produced the new element by bombarding a plutonium-242 target with neon-22 ions, although this was later put into question.

[23] More conclusive evidence was obtained by researchers at the University of California, Berkeley, who synthesised element 104 in 1969 by bombarding a californium-249 target with carbon-12 ions.

After various compromises were attempted, in 1997, IUPAC officially named the element rutherfordium following the American proposal.

[26] Like other groups, the members of this family show patterns in their electron configurations, especially the outermost shells, resulting in trends in chemical behavior.

Most of the chemistry has been observed only for the first three members of the group; chemical properties of rutherfordium are not well-characterized, but what is known and predicted matches its position as a heavier homolog of hafnium.

When finely divided, their reactivity shows as they become pyrophoric, directly reacting with oxygen and hydrogen, and even nitrogen in the case of titanium.

Zirconium and hafnium are in particular extremely similar, with the most salient differences being physical rather than chemical (melting and boiling points of compounds and their solubility in solvents).

All the stable members of the group are silvery refractory metals, though impurities of carbon, nitrogen, and oxygen make them brittle.

This, along with the higher melting and boiling points, and enthalpies of fusion, vaporization, and atomization, reflects the extra d electron available for metallic bonding.

[41] Alloys with zinc are magnetic at less than 35 K.[1] Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium[42] in that they have the same number of valence electrons and are in the same group.

Also, their relativistic effects are similar: The expected expansion of atomic radii from period 5 to 6 is almost exactly canceled out by the lanthanide contraction.

[42] Rutherfordium is expected to be a solid under normal conditions and have a hexagonal close-packed crystal structure (c/a = 1.61), similar to its lighter congener hafnium.

The formation of oxides, nitrides, and carbides must be avoided to yield workable metals; this is normally achieved by the Kroll process.

Further purification is done by a chemical transport reaction developed by Anton Eduard van Arkel and Jan Hendrik de Boer.

[48][49][50][51][52] Titanium metal and its alloys have a wide range of applications, where the corrosion resistance, the heat stability and the low density (light weight) are of benefit.