Bohr's Atomic Theory & Modern Atomic Theory

Bohr's Atomic Theory

1. Electron Orbits

   • Electrons move in circular orbits at specific distances from the nucleus.
   • These orbits are referred to as energy levels or shells.
   • Electrons have both kinetic and potential energy while moving in these orbits.

2. Energy Levels

   • As the distance from the nucleus increases, the energy of the orbits also increases.

3. Ground State

   • Electrons reside in their lowest possible energy level unless excited.
   • This lowest energy state is called the ground state.

4. Excited State

   • When energy is given to an atom, electrons can move to higher energy levels, referred to as the excited state.
   • An excited atom is unstable.

5. Absorption

   • When an atom absorbs energy, electrons jump between orbits, with the absorbed energy equaling the energy difference between the two levels.

6. Emission

   • Excited atoms release excess energy by emitting radiation, allowing electrons to fall to lower energy states.

7. Limitations of Bohr's Theory

   • Inadequate for multi-electron systems.
   • Only valid for hydrogen atoms and single-electron ions.
   • Does not explain the wave-particle duality of electrons.
   • Heisenberg's uncertainty principle suggests electrons do not have well-defined orbits but probability distributions.

Modern Atomic Theory

1. Quantum Mechanics and Orbitals

   • Exact positions of electrons cannot be determined, consistent with Heisenberg's uncertainty principle.
   • Electrons are found within regions called orbitals, which have different shapes and sizes.

2. Three-dimensional Movement

   • Electrons exhibit three-dimensional movement around the nucleus.
   • Movement is probabilistic, not fixed paths.

Key Concepts

• Bohr's Atomic Model

  • Describes electrons in circular orbits.
  • Limitations include applicability only to hydrogen and failure to account for multi-electron systems.

• Modern Atomic Model

  • Incorporates quantum mechanics, probability, and three-dimensional electron movement.
  • Defines regions called orbitals.

• Heisenberg's Uncertainty Principle

  • States that the exact position and velocity of an electron cannot be simultaneously known.
  • Impacts the understanding of electron behavior in atoms.

• Comparison Concepts

  • Bohr's Concepts: Planar motion, orbit.
  • Modern Concepts: Orbital, probability, three-dimensional motion.