Electronic Configuration of Transition Metals for NEET: Key Points, Tricks & MCQs

What NEET Asks

• Direct Configuration: Identify correct configurations for atoms and ions, a frequent question type.
• Exceptions: Questions on anomalous configurations of Cr and Cu are common and high-yield.
• Properties Link: Relate electronic configuration to magnetic properties or stability, often as part of a multi-concept question.

Key Points

• General Configuration: The general outer electronic configuration for transition metals is (n-1)d¹⁻¹⁰ ns¹⁻². Here, n refers to the outermost shell.
• Orbital Filling: Electrons generally fill the ns orbital before the (n-1)d orbitals according to the Aufbau principle.
• Electron Removal: When forming cations, electrons are always removed first from the outermost ns orbital, then from the (n-1)d orbital.
• Stability Rule: Half-filled (d⁵) and fully-filled (d¹⁰) d-orbitals provide extra stability due to symmetry and exchange energy.
• Exceptions (Cr, Cu): Chromium (Z=24) has the configuration [Ar]3d⁵4s¹ (not 3d⁴4s²). Copper (Z=29) has [Ar]3d¹⁰4s¹ (not 3d⁹4s²).

Must-Know Formula / Reaction

General Electronic Configuration: (n-1)d¹⁻¹⁰ ns¹⁻²

• (n-1)d: Represents the penultimate d-subshell, holding 1 to 10 electrons.
• ns: Represents the outermost s-subshell, holding 1 or 2 electrons.

Common Mistakes

• Students often forget the crucial exceptions for Chromium and Copper, applying the Aufbau principle strictly.
• Don't confuse the order of electron filling (Aufbau) with the order of electron removal from ions (always ns first).
• Mistakenly removing electrons from (n-1)d before ns when deriving configurations of transition metal cations.

Rapid Revision

Master (n-1)d¹⁻¹⁰ ns¹⁻². Crucially, for ions, remove ns electrons first, then (n-1)d. Always remember Cr (3d⁵4s¹) and Cu (3d¹⁰4s¹) exceptions; they're high-frequency NEET targets.