Atomic Models and Bohr's Atomic Model

Introduction

• Various atomic models proposed by eminent scientists to understand atomic structure.
• Rutherford's model: Electrons revolve around the nucleus in well-defined orbits.
• Problem with Rutherford’s model: Unstable electron motion due to emission of electromagnetic radiation, causing electrons to lose energy and fall into the nucleus.

Niels Bohr's Atomic Model (1913)

• Proposal: Electrons revolve around the nucleus in specific orbits or shells associated with definite energies.

Key Features

1. Electron Shells
   • Orbits or shells represented by K, L, M, N.
   • Maximum number of electrons in an orbit is calculated by $2n^2$:
     • K shell: 2 electrons
     • L shell: 8 electrons
     • M shell: 18 electrons
     • N shell: 32 electrons
2. Outermost Shell
   • Maximum electrons in the outermost shell: 8
3. Energy of Orbits
   • Closest orbit to the nucleus has minimum energy.
   • Farthest orbit has maximum energy.

Energy Radiation and Electron Excitation

• Electrons do not radiate energy while moving in their specific orbits.
• Energy Absorption and Emission
  • Electrons absorb energy, get excited, and jump to higher energy levels.
  • Electrons radiate energy and return to lower energy levels.

Significance

• Bohr's model is easy to understand and works well for simple atoms.
• Still in use today along with the quantum mechanical model.

Summary: Things to Remember

• Bohr proposed the model in 1913.
• Electrons revolve in definite energy levels or shells.
• Maximum electrons per orbit: $2n^2$.
• Maximum electrons in outermost shell: 8.
• Closest orbit has minimum energy; farthest has maximum.
• Electrons absorb and radiate energy to move between energy levels.