The elements which lie in between the Group IIA elements and the Group II B elements in the modern periodic table are known as the d block elements. The d-block elements are sometimes also known as the transition elements.
Electronic configuration of an element is defined as an arrangement of electrons in the orbital. Orbital s, p, d, and f are the four principal atomic orbitals which should be filled according to the number of electrons and the energy level of the orbital. The four orbitals can be arranged according to their energy level as s< p< d< f. According to Aufbau’s principle the lowest energy orbital should be filled first. The s orbital can acquire two electrons whereas p, d and f orbitals can hold 6, 10and 14 electrons respectively. The electronic configuration of first row transition element is shown in the table below:
|Atomic number||Symbol||Electronic configuration|
So we generalize the outer configuration of first row transition elements as 4s2 3dn. But from the above table we can see that chromium and copper do not follow this pattern. This is because of very little energy difference between the 3d shell and 4s shell. It is experimentally found that half and completely filled sets of orbitals are more stable. In the case of chromium and copper the energy difference between the orbitals is very less so it is unable to prevent the electrons entering in the d shell. The electronic configuration of d-block element in the modern periodic table can be written as shown in the table below:-
Zn, Cd and Hg have their orbitals completely filled both in their ground state and in their common oxidation states and is represented as (n-1) d10 ns2. So, they are not referred to as transition elements.
This information on electronic configuration of d-block elements is described briefly. Read more about S-Block Elements.