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SUBJECT-CHEMISTRY
CHAPTER-ATOMIC STRUCTURE
SUBTOPIC- Achievements Bohr's atomic model, limitation of Bohr's atomic
model.
KEY NOTES:
It explains the stability of atom :
According to this theory an electron cannot lose energy as long as it
revolves in a particular orbit. Therefore the question of losing energy
continuously and falling into the nucleus does not arise.
It explains the line spectrum of hydrogen :
When an electric discharge is passed through gaseous hydrogen, the H2
molecules dissociate and the energetically excited hydrogen atoms
produced emit electromagnetic radiation of discrete frequencies. The
hydrogen spectrum consists of several series of lines named after their
discoverers. Balmer showed in 1885 on the basis of experimental
observations that if spectral lines are expressed in terms of
wavenumber , then the visible lines of the hydrogen spectrum obey
the following formula :
where n is an integer equal to or greater than 3 (i.e., n = 3,4,5,....)
The series of lines described by this formula are called the Balmer
series. The Balmer series of lines are the only lines in the hydrogen
spectrum which appear in the visible region of the electromagnetic
spectrum. The Swedish spectroscopist, Johannes Rydberg, noted that
all series of lines in the hydrogen spectrum could be described by the
following expression :
