The d-And-f-Block Elements

The chromate ion (CrO₄^2–) has a tetrahedral shape, whereas dichromate ion has two tetrahedral units with one common oxygen having Cr—O—Cr bond angle of 126°.

In the case of p-block elements the valence electron are in np orbital. In this case, the valence electrons get unpaired and then excited to vacant d-orbital of the same energy level. Thereby exhibit variable oxidation state, e.g., in halogens.




But in the case of d-block elements these and (n – 1) d-electrons are lost. For example, Sc has the configuration [Ar]3d¹s². Therefore, it 4s electrons are lost it shows +2 and if in addition to 4s, 3d electrons are also lost than +3. Therefore, in the case of p-block elements the two oxidation states differ by two units, whereas in the case of d-block elements it differs by one unit only.

Transition metal fluorides are ionic in nature, because the difference in electronegativities of transition metal and fluorine is quite large. On the other hand, the difference in electronegativities of transition metal and bromine (or chlorine) atom is less and hence, transition metal bromides and chlorides and covalent in nature.

When we move downward in a particular group the atomic number is increased, consequently nuclear charge is also increased. Due to this reason 5d-elements have higher nuclear change than 3d and 4d elements, therefore, the outer electrons are attracted strongly by the nucleus in 5d elements. On the other hand, the shielding effect of 4f electrons is very poor due to lanthanide contraction in 5d elements, which further increases from 5d elements than 3s and 4d electrons, where no 4f electrons and lanthanide contraction is present.