The Electronic Configuration of The Transition Elements in The Modern Periodic Table

Introduction

The elements in the periodic table are mainly divided into four distinct groups: (1) main group elements, (2) transition metals, (3) lanthanides, and (4) actinides. The main group elements comprises all the active metals in the two columns on the extreme left of the periodic table and the metals, semimetals, and non-metals in the six columns on the extreme right. The transition metals are the metallic elements that act as a bridge, or transition, between the two sides of the table. The lanthanides and the actinides present at the bottom of the table are sometimes referred to as the inner transition metals because they have atomic numbers that lie between the first and second elements in the last two rows of the transition metals.

Exceptions to the Transition Elements

A transition metal refers to one that forms one or more than one stable ions that possess incompletely filled d orbitals. Based on this definition, scandium and zinc are not considered as transition metals even though they are members of the d block.

• Scandium has the electronic structure [Ar] 3d14s2. Whenever it forms ions, it always tends to lose the three outer electrons and results in the formation of  an argon structure. The Sc3+ ion possesses no d electrons and thus it does not follow the definition.

• Zinc has the electronic structure [Ar] 3d104s2. When it forms ions, it always loses the two 4s electrons to form a 2+ ion with the electronic structure [Ar] 3d10. The zinc ion has fully filled d orbitals and it does not meet the definition either.

As compared to, copper, [Ar] 3d104s1, forms two ions. In the Cu+ ion the electronic structure is represented by [Ar] 3d10. Although, the more common Cu2+ ion has the structure [Ar] 3d9. Copper  definitely represents a transition metal as the Cu2+ ion has an incomplete d level.

Electronic Configuration of the Transition Elements

The valence electronic configuration for first series transition metals (i.e. Groups 3 – 12) is generally 3dn4s2.

Exceptions:  The electron configurations for chromium (3d54s1) and copper (3d104s1) represent some of the exceptions. This is mainly because 3d and 4s orbitals are very close in energy, and the energy of 3d orbitals decreases on moving across the row. For both chromium and copper the configuration possessing more electrons in 3d orbitals is usually of lower energy. 

For chromium this is mainly due to the difference in 3d and 4s orbital energies is same as the pairing energy (electron pairs are of higher energy).

The  3d54s1 configuration has lower energy as this configuration has the maximum number of unpaired electrons in a d-subshell. In copper (near the end of the transition series) 3d orbital energy has decreased so that 3d orbitals are of lower energy than that of 4s orbitals.

This means that the 3d104s1 configuration is of lower energy since it has more electrons in 3d orbitals. For the transition metal atoms, the total number of valence electrons is equal to the number of the column (or group) in the periodic table (counting from the left). For transition metal ions that have charge ≥ +2, the number of d electrons is equal to the total number of valence electrons subtracted from the charge on the ion.

This is because orbitals in the 3d and 4s subshells are of the same energy. In transition metal atoms the 4s subshell has lower energy than the 3d subshell. While in transition metal ions of charge ≥ +2, 3d is of lower energy than 4s. In transition metal ions of charge ≥ +2, all valence electrons are in the d-subshell. Thus, Ni (present in Group 10) possess 10 valence electrons and Ni2+ is d8 Fe (present in Group 8) possess 8 valence electrons and Fe3+ is d5 , Ti (in Group 4) possess 4 valence electrons and Ti3+ is d1.

Conclusion

The electronic configuration of transition metals is special in the case that they can be found in various oxidation states. However, the elements can possess various different oxidation states, they mainly exhibit a common oxidation state based on what makes that element most stable. Here we come to an end of this topic hope you were able to grasp a clear concept on the electronic configuration of the transition elements.