Read Electron Configuration Before Ranking Paramagnetism
Both isoelectronic-species matching and paramagnetism ranking need the same first step — write out the actual electron configuration of each species, including for ions, before comparing anything.
Isoelectronic Species and Magnetic Properties is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Isoelectronic doesn't mean same element or same charge
C2²⁻, NO+, CN- and O2²⁺ can all be isoelectronic (same total electron count, here 14) despite being completely different species built from different elements and charges — always count total electrons directly rather than looking for a formula pattern.
Paramagnetism ranks by unpaired electron count
Comparing Al, Mg, O and N for paramagnetism means writing each one's electron configuration and counting unpaired electrons: Mg (all paired, diamagnetic) < Al (1 unpaired) < O (2 unpaired) < N (3 unpaired, half-filled 2p3) — more unpaired electrons means stronger paramagnetism, and N's half-filled subshell gives it the most among this set.
Maximum unpaired electrons among transition-metal-adjacent species
Among Na, Mn, Cr and Fe2+, Cr ([Ar]3d5 4s1) has 6 unpaired electrons — more than Mn2+-type or Fe2+ configurations in many comparisons — because Cr's actual ground-state configuration is an exception to the simple filling order (one 4s electron moves into 3d to achieve the extra-stable half-filled d5 configuration), which is exactly the kind of configuration exception this cluster tests.
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- ✓Isoelectronic species share total electron count only — not element, charge, or formula pattern.
- ✓Paramagnetism strength ranks by unpaired electron count — write out the actual configuration for each species being compared, especially for ions.
- ✓Cr and Cu are classic configuration exceptions (one s-electron moves to achieve a half-filled or fully-filled d-subshell) — remember these when counting unpaired electrons.
Don't assume two ions are isoelectronic just because their formulas look similarly structured — always count total electrons explicitly, especially when comparing species built from different elements and different charges.
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