Transition metals are metals that possess unique and useful properties, mostly consisting of d-block transition elements in the periodic table.
There are about 56 transition elements that are subdivided into three main groups:
- Main transition elements or d block elements (DBE)
- Lanthanides elements
- Actinides elements
Transition metals have incomplete inner electron shells that serve as transitional links between the most and the least electropositive in a series of elements. They are characterized by:
- Multiple valences
- Colored compounds
- Ability to form stable complex ions
General properties of transition metals:
- Multiple oxidation states: Most transition metals have multiple oxidation states, since it is relatively easy for transition metals to lose electron(s) compared to the alkali metals and alkaline earth metals.
- High melting point and boiling point: The bonding between the atoms in transition metals is very strong. The strong attractive force between the atoms is only weakened at high temperatures, hence the high melting points and boiling points.
- High density: The strong bonding between the atoms in transition metals cause them to be tightly held together, creating a high density.
- Colored compounds: Transition metals tend to form more colored compounds than other elements, either in solid form or dissolved in a solvent. For example, vanadium (III) chloride (VCl3) is green, cobalt sulphate (CoSO4) is pinkish, copper (II) sulphate (CuSO4) is deep blue.
- Catalytic properties: The transition metals and their compounds are known for their homogeneous and heterogeneous catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium (V) oxide (in the contact process), finely divided iron (in the Haber process), and nickel (in catalytic hydrogenation) are some examples.
Other properties include:
- They are all metals and form alloys with one another.
- Many of them dissolve in mineral acids, while few are unaffected by simple acids.
- They form some paramagnetic compounds.
- They are all shiny metals.
- They are all good conductors of heat and electricity.