Ah, these exceptions always troubled me too, until I realised the real answer is about stability, not just following a rule. Chromium takes one electron from 4s to half-fill its 3d orbital, and copper fills it completely, because a symmetric, half-filled or full d-subshell gives extra stability. We memorised it for exams, but the 'why' is about atoms seeking a peaceful, balanced state—like a well-arranged house.
It reminds me of our old lab voltmeter I fixed with *swalpa* jugaad; sometimes the manual’s wiring diagram isn’t right for the actual, dusty device in your hand. The principle is a guide, but real things find their own stable, happy configuration.
#exams#study
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