Atomic Spectra Lab 1

Light If we pass light through a prism or diffraction grating, we can see the intensity as a function of wavelength.

Type of Spectrum Solids, liquids, and dense gases emit light of all wavelengths, without any gaps – or a continuous spectrum

Thin gases emit light of only a few wavelengths - an emission or bright line spectrum.

If there is a source of light behind it, a thin gas will absorb light of the same wavelengths it emits this is called an absorption or dark line spectrum.

Different Emission Line Spectra H He C

Balmer lines each element generates its own unique set of wavelengths of emission or absorption Balmer studied the optical spectrum of hydrogen and found a pattern in the wavelengths of its emission lines

Periodic Table of Elements

Balmer series – set of visible lines in H spectrum For H, the wavelengths are - 374.9 377.0 379.7 383.4 388.8 396.9 410.1 433.9 486.0 656.1 a simple formula reproduces these wavelengths λ (n) = (364.5 nm * ( n2 /n2 – 4)) where n = 3, 4, 5, …..

other scientists found similar patterns in other portions of the electromagnetic spectrum

Paschen series Paschen, in the infrared, measured lines with wavelengths 866.2 874.8 886.0 901.2 922.6 954.3 1004.6 1093.5 1281.4 1874.5 which matched the series λ (n) = (820.5 nm * ( n2 /n2 – 9)) where n = 4, 5, 6, …..

Lyman series Lyman, in the ultraviolet, a series of lines with wavelengths 91.9 92.1 92.3 92.6 93.0 93.7 94.9 97.2 102.5 121.5 corresponding to the series λ (n) = (91.1 nm * ( n2 /n2 – 1)) where n = 2, 3, 4, …..

In fact, scientists soon realized that hydrogen's spectrum could be broken down into a large number of series, each of which had wavelengths obeying a formula like Λ (n,k) = (limit) * ( n2 /n2 – k2)) where n=k+I, k+2,…. The Lyman series corresponds to k=1 with a limit of 91.1 nm, the Balmer series to k=2 with a limit of 364.5 nm, and so forth