Emission and Absorption Spectra
Introduced| English |
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| spectrum/ˈspektrəm/ |
A barcode of light that names the element
- Split the light from a glowing gas and you don't get a rainbow — you get a few sharp coloured lines.
- The exact set of lines is different for every element — a barcode that names it.
- These spectra 光谱 come straight from the electron energy levels of the Bohr model.
- Astronomers read them to tell what distant stars are made of.
Emission spectra
- Heat or excite a gas and its electrons jump up, then drop back down, emitting photons.
- Each drop emits one exact frequency, so you see bright lines on a black background.
- The emission spectrum is the set of frequencies that element gives off.
- Because the levels are unique, the line pattern is a fingerprint of the element.
Lines from level jumps
Pick two levels and see the spectral line that a jump between them produces.
An emission spectrum shows:
Electrons dropping down emit photons, giving bright lines on black.
Because each element has unique energy levels, its spectrum acts as a ____.
The unique line pattern identifies the element like a fingerprint.
Absorption spectra
- Shine white light through a cool gas and the gas absorbs the frequencies its electrons can jump on.
- Those exact frequencies go missing, leaving dark lines in the otherwise continuous spectrum.
- The dark absorption lines fall at the same frequencies as that element's bright emission lines.
- So both spectra reveal the same fingerprint, one in light, one in shadow.
An absorption spectrum shows:
The gas absorbs certain frequencies, leaving dark lines in the continuous spectrum.
For a given element, its absorption lines fall at the same frequencies as its emission lines.
Both come from the same energy-level gaps, so they share the same frequencies.
Select all true statements about spectra.
Emission = bright, absorption = dark, at the same frequencies. Each element's spectrum is unique.
Reading the stars
- Sunlight has dark absorption lines from gases in the Sun's outer layers.
- Matching them to known elements tells us what the Sun (and other stars) contain.
- The element helium was discovered in the Sun's spectrum before it was found on Earth.
- Spectra turn a point of light into a full chemical analysis.
Astronomers use spectral lines to identify the elements in distant stars.
Matching a star's absorption lines to known elements reveals its composition.
Emission and absorption lines for the same element sit at the same frequencies — one shows them bright (emitted), the other dark (absorbed). Don't treat them as unrelated: they are two views of the same set of energy-level gaps.
An unknown gas glows with bright lines at exactly the frequencies of hydrogen's spectrum. What is the gas?
- The line pattern is hydrogen's unique fingerprint, so the gas is hydrogen.
- Cool hydrogen would show dark lines at those same frequencies in absorption.
Emission spectra show bright lines (electrons dropping down, emitting photons); absorption spectra show dark lines (electrons absorbing photons from white light). Both fall at the same frequencies — a unique fingerprint of the element. Astronomers use them to identify what stars are made of.