4.1 Position of d-block elements in the periodic table:#
We have already learnt the periodic classification of elements in XI std. the transition metals occupy from group - 3 to group- 12 of the modern periodic table.
d- Block elements composed of 3d series (4th period) Scandium to Zinc (10 elements), 4d series (5th period) Yttrium to Cadmium (10 elements) and 5d series (6th period) Lanthanum, Hafnium to mercury. As we know that the group- 12 elements Zinc, Cadmium and Mercury do not have partially filled d- orbital either in their elemental state or in their normal oxidation states. However they are treated as transition elements, because their properties are an extension of the properties of the respective transition elements. As per the IUPAC definition, the seventh period elements, starting from Ac, Rf to Cn also belong to transition metals. All of them are radioactive. Except Actinium; all the remaining elements are synthetically prepared and have very low half life periods.