The electrical configuration of D block elements is (n-1)d1-10 ns1-2. Half-filled orbitals and entirely filled d orbitals are both stable for these elements. The electronic configuration of chromium, which includes half-filled d and s orbitals in its configuration—3d 4s—is an example of this.
Copper's electronic configuration is another example. Copper has a 3d10 4s1 electronic arrangement rather than a 3d9 4s2. The relative stability of the entirely filled d orbital can be due to this. In both their ground and general oxidation states, zinc, mercury, cadmium have totally filled orbitals. As a result, these metals aren't classified as transition elements, while the rest are classified as d block elements.
- Period 4, transition elements' electronic configuration is (Ar) 4s³1-2 3d1-10.
- Period 5, transition elements' electronic configuration is (Kr) 5s1-2 4d1-10.
- Period 6, transition elements' electronic configuration is (Xe) 4s1-2 3d1-10.
According to the Aufbau principle and Hund's rule of multiplicity, electrons are added to the 3d subshell from left to right along the period.
| Element | Electronic Configuration |
|---|---|
Sc | 4s2 3d1 |
Ti | 4s2 3d2 |
V | 4s2 3d3 |
CR | 4s1 3d5 |
Mn | 4s2 3d5 |
Fe | 4s2 3d6 |
Co | 4s2 3d7 |
Ni | 4s2 3d8 |
Cu | 4s1 3d10 |
Zn | 4s2 3d10 |
All of the series have anomalies, which can be explained by the following considerations.
- The distance between the ns and (n-1) d orbitals in terms of energy.
- Half-full orbitals are more stable than partially filled orbitals.
- Pairing energy for electrons in s-orbitals.
Chromium has a 4s1 3d5 electron configuration rather than a 4s2 3d4 electron configuration, while copper has a 4s1 3d electron configuration rather than a 4s2 3d9. The stability of half-full orbitals relative to partly filled orbitals explains these oddities in the first transition series.
From niobium onwards, electron presence in d orbitals appears to be preferred over electron sharing in s orbitals in the second series of transition metals. The electron can choose between sharing in the s orbital or being stimulated to the d orbital from the available s and d orbitals. Obviously, the choice is determined by the amount of repulsive energy overcome during sharing and the energy difference between the s and d-orbitals.
Because the s and d-orbitals have about the same energy in the second series, electrons choose to occupy the d-orbital. As a result, s-orbital has only one electron in niobium. Transition metals of the third series, on the other hand, have a higher number of paired s configurations, even at the expense of half-filled orbitals. This series follows the filling of 4f orbitals and the lanthanide contraction that follows.
Atomic and Ionic Radii of d-Block Element
- Atomic and ionic radii of d-block elements decrease across a period due to increasing effective nuclear charge.
- Within a period, slight variations may occur due to changes in electron configuration and shielding effects.
- Across a group, atomic and ionic radii of d-block elements tend to increase due to the addition of new energy levels.
- Generally, d-block elements have smaller atomic and ionic radii compared to s-block and p-block elements due to higher effective nuclear charge and complex electron configurations.