i. When electric discharge is passed through gaseous hydrogen, it emits radiation. The recorded spectrum of this emitted radiation is called hydrogen emission spectrum.
ii. This spectrum falls in different regions of electromagnetic radiation and it is comprised of a series of lines corresponding to different frequencies. That is, the spectrum was discontinuous.
iii. In the year, 1885, Balmer expressed the wave numbers of the emission lines in the visible region of electromagnetic spectrum by the formula :
\(\bar V\) = 109677 [\(\frac{1}{2^2}-\frac{1}{n^2}\)] cm-1
Where, n = 3, 4, 5,…
These lines are known as Balmer series.
iv. Rydberg found that other series of lines could be described by the following formula :
\(\bar v\) = 109677 [\(\frac{1}{n_1^2}-\frac{1}{n_2^2}\)] cm-1
Where, 109677 cm-1 is called Rydberg constant for hydrogen (RH).
v. Different series of emission spectral lines for hydrogen are as follows :
| Series |
n1 |
n2 |
Region |
| Lyman |
1 |
2, 3, 4, …. |
Ultraviolet |
| Balmer |
2 |
3, 4, 5, …. |
Visible |
| Paschen |
3 |
4, 5, 6, …. |
Infrared |
| Bracket |
4 |
5, 6, 7, …. |
Infrared |
| Pfund |
5 |
6, 7, 8,…. |
Infrared |
