The d-block transition elements are the thirty metals found in the centre of the periodic table. They form three series of ten elements each: from scandium to zinc; from yttrium to cadmium; and from lanthanum to mercury. Elements from unnilquadium onwards are expected to form a fourth transition series. Most of them are hard, strong, shiny metals, and they are widely used in alloys.
They are further characterized by having high melting and boiling points - tungsten's melting point of 3422 degrees Celsius is the second highest of all the elements - although there are obvious exceptions to this; most strikingly, mercury, which is liquid at room temperature.
The series members are also good conductors of heat and electricity; copper, silver and gold are particularly proficient in this respect. Most of them will dissolve in hydrochloric, sulphuric and nitric acids, although some, such as platinum and gold, are extremely resistant to acidic attack, and are called 'noble' metals, 'nobility' being used to indicate inertness, in allusion to this fact.
Transition metals are also characterized by variable valency. Whereas some groups have a dominant oxidation state - group 2's is +2, for example - the transition elements tend to form compounds with varying numbers of bonds. Iron, for example, forms both iron (II) and iron (III) compounds.
A further characteristic of these elements is that they tend to form coloured compounds. Compounds such as zinc oxide and titanium dioxide are widely used in pigments.
