Final answer:
Absorption spectra show dark lines where light is absorbed by gases, creating Fraunhofer lines, while emission spectra show bright lines where gases emit light. Both spectra display lines at the same wavelengths for a given element, reflecting electron transitions between energy levels. Dark lines in absorption spectra remain because reemitted light is scattered away from the observer.
Step-by-step explanation:
Absorption spectra display dark lines on a bright background because they represent the specific wavelengths of light that are absorbed by a gas when white light passes through it. These dark lines are known as Fraunhofer lines. Conversely, emission spectra exhibit bright lines on a dark background, which correspond to the wavelengths of light that are emitted by a gas. The relationship between absorption and emission spectra is that the positions of the dark lines in the absorption spectra correspond precisely to the positions of the bright lines in the emission spectra for a given element.
This means atoms of a specific element absorb and emit radiation at exactly the same wavelengths. These patterns, known as the element's spectral signature, are unique to each element. Niels Bohr's model helped explain these phenomenons for hydrogen, revealing that light is emitted or absorbed when an electron transitions between quantized energy levels within an atom.
The fact that both spectra show the same wavelengths for an element indicates that absorbed photons cause an electron to move from a lower energy level to a higher one (absorption), and when an electron falls back down (emission), it emits a photon of the same wavelength. However, dark lines in an absorption spectrum remain dark because the reemitted light from the gas is scattered in all directions, and essentially not all of it is redirected back toward the observer.