| Group 4 in the periodic table | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| |||||||||
| ↓ Period | |||||||||
| 4 |  22 Transition metal | ||||||||
| 5 |  40 Transition metal | ||||||||
| 6 |  72 Transition metal | ||||||||
| 7 | Rutherfordium (Rf) 104 Transition metal | ||||||||
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Legend | |||||||||
Group 4 is the second group of transition metals in the periodic table. It contains the four elements titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). The group is also called the titanium group or titanium family after its lightest member.
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. Due to the effects of the lanthanide contraction, they are very similar in properties. Titanium is somewhat distinct due to its smaller size: it has a well-defined +3 state as well (although +4 is more stable).
All the group 4 elements are hard, refractory metals. 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. The first three of them occur naturally. 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. None of them have any biological role.