Transition metals (groups 3–12)

Where they sit: the d-block

In these metals, electrons fill an inner d subshell while the outer s orbital usually holds two electrons, as in iron ([Ar] 3d⁶ 4s²). Chromium ([Ar] 3d⁵ 4s¹) and copper ([Ar] 3d¹⁰ 4s¹) are exceptions, because half-filled and full d subshells are especially stable. When forming ions the metals lose their s electrons first, so Fe²⁺ is [Ar] 3d⁶.

This site shows lanthanum, lutetium, actinium and lawrencium with the lanthanides and actinides. Zinc, cadmium and mercury keep a full d subshell in their common compounds, so some chemists exclude them, but most periodic tables include them.

Typical properties

Most transition metals are hard, dense and shiny, with high melting points. Tungsten has the highest melting point of any metal, 3422 °C, and osmium is the densest element ever measured, at 22.59 g/cm³, while mercury is a liquid that melts at −39 °C. Because their d electrons can take part in bonding, most have several oxidation states: iron forms Fe²⁺ and Fe³⁺, and manganese reaches +7 in the permanganate ion, MnO₄⁻. Their compounds are often colored, like blue copper(II) sulfate, and iron, cobalt and nickel are ferromagnetic.

Trends and typical reactions

Trends are gentler than in the main groups, because the extra electrons go into an inner subshell and atomic size changes little across a period. The lanthanide contraction makes period 6 metals almost the same size as those of period 5, so zirconium and hafnium are hard to separate.

A more reactive metal displaces a less reactive one from solution: Fe + CuSO₄ → FeSO₄ + Cu. Zinc reacts with dilute acids (Zn + 2HCl → ZnCl₂ + H₂), but copper, silver and gold do not. Many transition metals are catalysts: iron speeds up the Haber process for ammonia, and platinum, palladium and rhodium clean car exhaust in catalytic converters.

Everyday uses

Iron, mostly as steel, is the most widely used metal, and chromium and nickel make it stainless. Copper carries electricity in wires, titanium is used in aircraft and hip replacements, zinc protects steel from rust, and gold, silver and platinum go into jewelry and electronics.

Rutherfordium to hassium are radioactive and have only been made a few atoms at a time. Meitnerium to copernicium (109–112) are expected to be transition metals too, but their properties are unmeasured, so this site lists them as unknown.