Electronic Configuration

Electronic Configuration

The electronic configuration of an atom describes the arrangement of electrons in its energy levels (shells) around the nucleus.

Rules for Writing Electronic Configuration

1. Aufbau Principle:

   • Electrons fill lower energy levels first, before moving to higher levels.

   • Order of filling:

     $$1s\to 2s\to 2p\to 3s\to 3p\to 4s\to 3d\to 4p\dots$$

2. Pauli Exclusion Principle:

   • An orbital can hold a maximum of two electrons with opposite spins.

3. Hund’s Rule:

   • Electrons occupy degenerate orbitals (same energy) singly first, then pair up.

4. Maximum Electron Capacity of Shells (Based on 2n² rule):

   • K shell (n=1) → max 2 electrons

   • L shell (n=2) → max 8 electrons

   • M shell (n=3) → max 18 electrons

   • N shell (n=4) → max 32 electrons

Electronic Configuration of First 20 Elements (Hydrogen to Calcium)

Diagram: Electronic Configuration of First 20 Elements

(A visual representation of atomic structures showing electron distribution in shells from Hydrogen to Calcium.)