Group 4

Group 4 (also called Group IVB of the transition metals) is one of the vertical columns of the periodic table of chemical elements. It contains titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). All of them are transition metals, meaning their valence electrons occupy d orbitals.

Elements of this group have two electrons in the outermost s orbital and two electrons in the d orbital. For this reason, the most common oxidation state is +4, which occurs when the element loses four electrons. Compounds with oxidation state +4 are the most stable, for example titanium dioxide (TiO₂) and zirconium dioxide (ZrO₂).

General properties

Titanium, zirconium, and hafnium are hard metals with high melting points that form a thin, light oxide layer in air. This layer prevents further oxidation and corrosion, so these metals typically appear resistant to corrosion, even though the elements are chemically reactive when measured in isolation. When finely divided or heated to high temperatures, they can become pyrophoric.

Zirconium and hafnium

Zirconium and hafnium have very similar atomic radii because of an effect called the lanthanide contraction. For this reason their chemistry is very similar, and they are difficult to separate. Natural zirconium ore always contains small amounts of hafnium. Their separation is important in nuclear power plants, because zirconium has very low neutron absorption, while hafnium absorbs neutrons strongly—consequently zirconium is used as cladding material and hafnium as a control element for fission.

Applications

Titanium and its alloys are used in aerospace, high-altitude applications, and medical devices such as implants, because of their low weight and good biocompatibility. Titanium dioxide is a bright white pigment widely used in paints, paper, and consumer products. Zirconium dioxide is used in hard ceramics and dental crowns.

Rutherfordium

Rutherfordium is a synthetic element produced in nuclear reactors. It does not occur naturally, and its isotopes are radioactive with very short half-lives. For this reason, chemical research is difficult, and only a tiny number of atoms can be produced at a time.