Emission and Absorption Spectra
Introduced| English | Meaning |
|---|---|
| spectrum/ˈspektrəm/ | A distribution of electromagnetic radiation according to wavelength or frequency. |
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Electrons dropping down emit photons, giving bright lines on black.
Because each element has unique energy levels, its spectrum acts as a ____.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Both come from the same energy-level gaps, so they share the same frequencies.
Select all true statements about spectra.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
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.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Write from lines at 410 nm and 434 nm
- A lab hydrogen lamp has bright lines at 410 nm and 434 nm.
- A star's spectrum has dark lines at those same two wavelengths. Say what that shows.
A hydrogen lamp in the lab has bright emission lines at 410 nm and 434 nm. A star's spectrum shows dark lines at 410 nm and 434 nm. What does the match show about the star?
The same wavelengths mean the same element.
What do the matching dark lines show?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Absorption at hydrogen's wavelengths means hydrogen is present.