Atomic Structure

• Bohrs Atomic Model

  1. Atom has centre called nucleus.
  2. Electrons revolve only in fixed circular orbits.
  3. Quantization condition : Electrons revolve only in those orbits where angular momentum of revolving electron is equal to the integral multiple of h/2pi
  4. While revolving electrostatic force between electron and nucleus provides centripetal force(Fc) = mv^2 /r
  5. While revolving in a particular orbit, an electron neither gains nor looses electron
  6. An electron gains or loose only those energy which are equal to difference in two energy levels.
• Neiel's Bohr's purposed an atomic model

  1913 AD
• Bohr's Atomic Model


  To overcome the limitation of Rutherford's Atomic Model
• Bohr's Atomic Model


  • Applied Planck's quantum theory of radiation to an atom
  • Electrons revolve around the positive charged nucleus in definite circular paths called orbits or energy levels
  • Electrons neither emit nor absorb energy as long as they remain in a particular orbit
  • Energy levels are represented by integer quantum numbers (n=1,2,3,...)
  • Electrons can only revolve in orbits where the angular momentum is an integral multiple of h/2π
• Origin of Hydrogen spectrum

  1. Hydrogen molecule dissociates to form hydrogen atoms

  2. Electrons in hydrogen atoms absorb different amounts of energy

  3. Excited electrons jump to higher energy levels

  4. Excited electrons jump back to ground state emitting radiation

  5. Different downward jumps emit radiation of different wavelengths producing spectral lines
• Spectral series


  Series of spectral lines produced by the different downward jumps of electrons in hydrogen
• Hydrogen contains only one electron