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Atoms, Molecules and Nuclei

Rutherford’s model of atom:

  • Most of the mass of the atom and all its positive charge are concentrated in a tiny nucleus, and the electrons revolve around this nucleus.
  • Limitations
    • It predicts that atoms are unstable because the accelerated electrons revolving around the nucelus must spiral into the nucleus. This contradicts the stability of matter.
    • It could not explain the characteristic line spectra of atoms of different elements.
  • Total energy of electron in hydrogen atom


Origin of Spectral Lines:

  • The atomic hydrogen emits a line spectrum consisting of various series. The frequency of any line in a series can be expressed as a difference of two terms:
  • Lyman series:
  • Balmer series:
  • Paschen series:
  • Bracket series:
  • Pfund series:


Bohr model of hydrogen atom

  • In a hydrogen atom, electrons can revolve only in…

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