Question

Why do transition elements (d-block) show variable oxidation states and magnetic properties?

Hint:

Greater the number of unpaired d-electrons, stronger is the paramagnetic behavior of a transition element.

Answer 1

Step 1: Variable Oxidation States in Transition Elements.
Transition elements (d-block elements) show variable oxidation states mainly because their (n−1)d and ns orbitals have nearly the same energy. Due to this small energy difference, electrons can be removed not only from the outer ns orbital but also from the inner (n−1)d orbitals during bond formation.

For example, iron (Fe) has the electronic configuration:
Fe: [Ar] 3d⁶ 4s²
It can lose two electrons from the 4s orbital to form Fe²⁺, and one more electron from the 3d orbital to form Fe³⁺. Hence, it exhibits +2 and +3 oxidation states.

Thus, the availability of both ns and (n−1)d electrons for bonding leads to multiple possible oxidation states in transition elements.

Step 2: Magnetic Properties of Transition Elements.
Transition elements show magnetic properties because they possess unpaired electrons in their (n−1)d orbitals. The presence of unpaired electrons results in paramagnetism.

The greater the number of unpaired electrons, the stronger the paramagnetic character. For example:
Mn²⁺ (3d⁵) has five unpaired electrons and shows strong paramagnetism.

If all electrons are paired, the substance becomes diamagnetic. The magnetic moment (μ) of transition elements can be calculated using the formula:
μ = √[n(n + 2)] BM
where n = number of unpaired electrons.

Conclusion.
Transition elements exhibit variable oxidation states because of the comparable energies of ns and (n−1)d orbitals, allowing different numbers of electrons to participate in bonding. They show magnetic properties due to the presence of unpaired electrons in their d-orbitals, which cause paramagnetism.