The Development of The Bohr Model

The Chemistry of Art > 2. The Structure of the Atom and Colours > The Development of The Bohr Model >

The development of the Bohr model of the atom from the hydrogen spectra and relate energy levels to electron shells

  • Atomic spectrum of Hydrogen
  • Produced via excitation of atoms and release of excess energy through emission of light of various wavelengths
  • Described as discrete line spectrum, indicating that only certain energies are possible which means that energy levels are quantized.
  • Max Planck formulated the relationship between frequency and energy in Quantum theory
    • Electromagnetic (EM) radiation is transmitted or absorbed in discreet units (quanta) often referred to as “photons”
    • The energy of photon (E) is directly proportional to its frequency (v)

E = hv

where   h – Planck’s constant (6.626 x 10-34 J-s)

v – frequency (in Hertz or s-1)

  • Neils Bohr applied Planck’s concept to explain the hydrogen spectrum by proposing a quantum model.

Quantum model of hydrogen atom

  • In a hydrogen atom, the electron moves around the nucleus only in certain allowed circular orbits
  • Using classical physics, Bohr was able to calculate the radii of such allowed orbits – later called as “Bohr orbit”
  • Bohr orbit – has symbol of a0 with corresponding value of 5.29 x 10-11 m
    – radius of the orbit of H atom closest to the nucleus
  • The energy levels (in Joules) available to the electron in H atom can be calculated using the equation derived by Bohr.

E = -2.178 x 10-18 J (z2/n2)

where:   Z – atomic number

n – integer