Page 33 - 11-chem-5

5.ATOMIC STRUCTURE eLearn.Punjab

Second line n1 = 2 n2 = 4

v =1.09678 × 107  1 - 1  =20.566x105m-1
 22 42 
 

Third line n1 = 2 n2 = 5

v =1.09678 × 107  1 - 1  =23.00x105m-1
 22 52 
 

Limiting line n1 = 2 n2 = ∞

v =1.09678 × 107  1 - 1  =27.421x105m-1
 22 ∞2 
 

The limiting line of Balmer series lies in U.V region, while other lines fall in visible region.
Similarly, we can calculate the wave numbers for all the lines of Paschen, Brackett and Pfund series.
These three series of lines lie in the infrared region.

5.5.7 Defects of Bohr’s Atomic Model

1. Bohr’s theory can successfully explain the origin of the spectrum of H-atom and ions like
He+1, Li+2 and Be+3, etc. These are all one electron systems. But this theory is not able to explain the
origin of the spectrum of multi-electrons or poly-electrons system like He, Li and Be, etc.
2. When the spectrum of hydrogen gas is observed by means of a high resolving power
spectrometer, the individual spectral lines are replaced by several very fine lines, i.e. original lines
are seen divided into other lines. The Hα- line in the Balmer series is found to consist of five -
component lines. This is called fine structure or multiple structure. Actually, the appearance of
several lines in a single line suggests that only one quantum number is not sufficient to explain the
origin of various spectral lines.

33