28/04/2026
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Electronic Configuration Explained
Electronic Configuration—how electrons are arranged in different energy levels (shells and subshells) of an atom.
➡️The arrangement follows three main rules:
Aufbau Principle
Electrons fill orbitals starting from lowest energy to highest (1s → 2s → 2p → 3s → 3p → 4s → 3d …).
Hund's Rule
Electrons occupy empty orbitals singly first with parallel spins before pairing.
Pauli Exclusion Principle
No two electrons in the same orbital can have the same spin.
➡️Examples from the chart:
Hydrogen → 1s¹
Carbon → 1s² 2s² 2p²
Oxygen → 1s² 2s² 2p⁴
Sodium → 1s² 2s² 2p⁶ 3s¹
Iron → [Ar] 4s² 3d⁶
➡️ Special cases like Chromium (Cr) and Copper (Cu) show slight exceptions for extra stability.
➡️Why it matters:
Determines chemical bonding
Explains reactivity & valency
Helps understand periodic trends
