Class 11th Chemistry - Atomic Structure

Atomic Structure - Class 11th Chemistry

Understanding the structure of atoms is fundamental to chemistry and modern physics.

Historical Development

• Dalton's Atomic Theory: Matter consists of indivisible atoms
• Thomson's Model: Plum pudding model with electrons embedded in positive sphere
• Rutherford's Model: Nuclear model with dense nucleus and orbiting electrons
• Bohr's Model: Planetary model with quantized energy levels

Quantum Mechanical Model

• Principal Quantum Number (n): Energy level and size of orbital
• Azimuthal Quantum Number (l): Shape of orbital (s, p, d, f)
• Magnetic Quantum Number (m): Orientation of orbital
• Spin Quantum Number (s): Spin of electron (+1/2 or -1/2)

Electronic Configuration

Rules for filling electrons:

• Aufbau Principle: Electrons fill lower energy orbitals first
• Pauli Exclusion Principle: No two electrons can have identical quantum numbers
• Hund's Rule: Electrons occupy degenerate orbitals singly before pairing

Practice Problems

1. Write the electronic configuration of oxygen (Z=8).
2. How many electrons can occupy the 3d subshell?
3. Find the quantum numbers for the last electron in chlorine.