Outline a laboratory procedure for producing and observing the atomic absorption spectrum of a gas.

(i) Describe the appearance of an atomic absorption spectrum.

(ii) Explain why the spectrum in (a) provides evidence for quantization of energy in atoms.

The principal energy levels of the hydrogen atom in electronvolt (eV) are given by

\[{E_n} = \frac{{13.6}}{{{n^2}}}\]

where n is a positive integer.

Determine the wavelength of the absorption line that corresponds to an electron transition from the energy level given by n=1 to the level given by n=3.

shine white light through;
a tube of the gas;
then observe with spectroscope/grating/prism;

(i) continuous spectrum crossed by dark lines;

(ii) dark lines formed by the absorption of photons;
the absorbed photons have specific/discreet wavelengths;
indicating discreet differences in energy;
which can only be explained by existence of energy levels;

\(E = 13.6\left[ {\frac{1}{{{1^2}}} - \frac{1}{{{3^2}}}} \right] = 12.1{\rm{eV}}\);
12.1eV=12.1×1.6×10^–19J =\(\frac{{hc}}{\lambda }\);
λ=102nm or 103nm;
Award [3] for a bald correct answer.