To what extent do electronic configuration decides the stability of oxidation state in the firstseries of transition elements? Illustrate with an example.

The stability of oxidation states in the first series of transition elements is largely determined by their electronic configuration. The electronic configuration refers to the arrangement of electrons in the energy levels or orbitals of an atom.

To understand this, let's take the example of the first series of transition elements, which includes elements like Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), and so on.

In these elements, the electrons are added to the 3d and 4s orbitals. The 3d orbitals have higher energy levels compared to the 4s orbitals. As we move across the series, the number of electrons in the 3d orbitals increases, while the number of electrons in the 4s orbitals remains constant.

The stability of oxidation states depends on the ability of the element to lose or gain electrons. Elements with a half-filled or completely filled d-orbital tend to be more stable in a particular oxidation state. This is known as the "half-filled or completely filled d-orbital stability rule."

For example, let's consider the element Chromium (Cr). Its electronic configuration is [Ar] 3d^5 4s^1. In its ground state, it has one unpaired electron in the 4s orbital and five unpaired electrons in the 3d orbital. However, when it forms compounds, it tends to lose the 4s electron first, resulting in an oxidation state of +2. This is because losing the 4s electron allows the 3d orbital to have a half-filled configuration, which is more stable.

Similarly, when Chromium gains electrons, it tends to gain three electrons to achieve a completely filled 3d orbital, resulting in an oxidation state of -3.

In summary, the stability of oxidation states in the first series of transition elements is determined by their electronic configuration. Elements with a half-filled or completely filled d-orbital tend to be more stable in a particular oxidation state. The example of Chromium illustrates how the electronic configuration influences the stability of oxidation states.