Dark lines in a continuous spectrum where an element absorbs the same wavelengths it would emit.
Practise Atomic Structure & Periodicity All Atomic Structure & Periodicity topics
When white light passes through a cool gas, the atoms absorb exactly the wavelengths they would emit when excited, leaving dark lines in the continuous spectrum. These dark absorption lines are the complement of the bright emission lines of the same element. Joseph von Fraunhofer observed dark lines in the solar spectrum in 1814, and they reveal the elements in the Sun's cooler outer atmosphere. Helium was first identified this way in the Sun before it was found on Earth. Absorption spectroscopy is used to measure trace metals in environmental and industrial samples.
Key ideas: When white light passes through a cool gas, dark lines appear at the same wavelengths that the atom would emit. This shows that the transitions are between the same fixed levels. Fraunhofer lines in sunlight identified elements in the sun's atmosphere, and helium was discovered there first.
Common mistakes and connections: Students think absorption lines are at different wavelengths than emission lines; for the same element they coincide (for transitions starting from the ground state). Absorbed energy is later re-emitted in random directions, so the lines appear dark. Atomic absorption spectroscopy uses this to measure metal concentrations by Beer-Lambert law.
Sodium vapour absorbs the same energies it would emit; the 2.1 eV jump from 3s to 3p corresponds to the yellow D line at 589 nm. The interactive lesson shows this as a live animation or chart.
Dark lines in starlight reveal which elements are present in the outer layers of the star.
Dark lines in a continuous spectrum where an element absorbs the same wavelengths it would emit.
Atomic Absorption Spectra is a intermediate topic in Atomic Structure & Periodicity. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Atomic Structure & Periodicity first: Work Function, Photon, Atomic Emission Spectra.
The next topics in Atomic Structure & Periodicity are Hydrogen Spectrum Series and Rydberg Equation.
Yes. The interactive lesson includes a self-check question on Atomic Absorption Spectra, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Atomic Absorption Spectra is topic 42 of 115 in Atomic Structure & Periodicity.