Electronic Configuration of the First 20 Elements
The electronic configuration for the first 20 elements of the periodic table describes the distribution of electrons in an atom's orbitals. The Aufbau principle, Pauli exclusion principle, and Hund's rule guide this arrangement.

1. Electronic Configurations
- **Hydrogen (H)**: 1s¹
- **Helium (He)**: 1s²
- **Lithium (Li)**: 1s² 2s¹
- **Beryllium (Be)**: 1s² 2s²
- **Boron (B)**: 1s² 2s² 2p¹
- **Carbon (C)**: 1s² 2s² 2p²
- **Nitrogen (N)**: 1s² 2s² 2p³
- **Oxygen (O)**: 1s² 2s² 2p⁴
- **Fluorine (F)**: 1s² 2s² 2p⁵
- **Neon (Ne)**: 1s² 2s² 2p⁶
- **Sodium (Na)**: 1s² 2s² 2p⁶ 3s¹
- **Magnesium (Mg)**: 1s² 2s² 2p⁶ 3s²
- **Aluminum (Al)**: 1s² 2s² 2p⁶ 3s² 3p¹
- **Silicon (Si)**: 1s² 2s² 2p⁶ 3s² 3p²
- **Phosphorus (P)**: 1s² 2s² 2p⁶ 3s² 3p³
- **Sulfur (S)**: 1s² 2s² 2p⁶ 3s² 3p⁴
- **Chlorine (Cl)**: 1s² 2s² 2p⁶ 3s² 3p⁵
- **Argon (Ar)**: 1s² 2s² 2p⁶ 3s² 3p⁶
- **Potassium (K)**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
- **Calcium (Ca)**: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²

2. Orbital Diagram
The orbital diagram visually represents the distribution of electrons in the orbitals. Each box represents an orbital, while arrows indicate electrons.
- **1s Orbital**: ↑↓
- **2s Orbital**: ↑↓
- **2p Orbitals**: ↑↓ ↑↓ ↑ (total of 6 electrons)
- **3s Orbital**: ↑↓
- **3p Orbitals**: ↑↓ ↑↓ ↑ (total of 6 electrons)
- **4s Orbital**: ↑↓
This arrangement reflects the gradual filling of orbitals as per the energy levels dictated by quantum mechanics