The series of elements, that are formed by filling the 3d, 4d and 5d shells of electrons, comprise the d-block elements. They are often called as transition elements because their position in the periodic table is between s-block and p-block elements. Their properties are transitional between the highly reactive metallic elements of the s-block, which form ionic compounds and elements of p-block which form covalent compounds. In s and p blocks electrons add to the last shell, in d-block electrons are added to the penultimate shell. Typically the transition elements have an incompletely filled d level. The zinc group has d10 configuration and compounds of these elements show some differences from other transition elements. The elements make up three complete rows of ten elements and an incomplete fourth row. The position of the incomplete fourth series is discussed along with the f-block elements.

GENERAL CHARACTERISTICS OF TRANSITION ELEMENTS

(i)Except for mercury, which is a liquid at room temperature all other elements are solid metals exhibiting all the characteristics of a metal.

(ii) The show variable oxidation states unlike s and p block elements.

(iii) They, and some of their compounds, show catalytic properties.

(iv) Their compounds are colored.

(v) They have great tendency to form complex compounds.

(vi) They form alloys and interstitial compounds.