ChemistryMediumClass 12

d-block Properties — Variable oxidation state, colour, magnetism

d & f-block Elements

JEE Qs

Hard

min

Focus on understanding the fundamental reasons (electron configuration, energy levels) behind each property rather than rote memorization of examples; this allows you to deduce properties for unfamiliar cases.

🧮 Key Formulas

µ = sqrt(n(n+2)) BM (Bohr Magneton)

✅ Key Points for JEE

1Transition metals exhibit variable oxidation states due to the participation of both (n-1)d and ns electrons in bonding, as their energies are very close. The highest oxidation state is often observed in the middle of a series (e.g., Mn in +7).
2The stability of various oxidation states is influenced by factors like lattice energy (for solids), hydration enthalpy (for aqueous solutions), and the formation of stable configurations (e.g., d0, d5, d10). Higher oxidation states are more stable with highly electronegative elements like F and O.
3Most transition metal ions are colored because of d-d electronic transitions, where electrons absorb energy from visible light to jump to higher energy d-orbitals. Ions with d0 or d10 configurations are typically colorless unless color arises from charge transfer transitions (e.g., MnO4-, Cr2O7^2-).
4Paramagnetism (attracted to magnetic field) in transition metal compounds arises from the presence of unpaired electrons. Diamagnetism (repelled by magnetic field) occurs when all electrons are paired. Ferromagnetism is a strong form of paramagnetism.

⚠️ Common Mistakes

✕Confusing the origin of color: d-d transitions occur in ions with partially filled d-orbitals, while charge transfer transitions explain the color of d0 or d10 ions (e.g., MnO4-, Cr2O7^2-).
✕Incorrectly determining the number of unpaired electrons, especially for ions in different oxidation states (remember ns electrons are removed before (n-1)d electrons).
✕Assuming all d-block elements or their ions are colored and paramagnetic; d0 (e.g., Sc^3+) and d10 (e.g., Zn^2+, Cu^+) ions are typically colorless and diamagnetic.

NCERT Chapters

Class 12 Chemistry Ch 8: The d- and f-Block Elements