Skip to content
CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Absorption spectrum

The dark lines left in a continuous spectrum when white light passes through a gas: atoms absorb only photons whose energy exactly matches a jump to a higher level. Absorption and emission between the same two levels occur at the same wavelength.

Energy levels of the hydrogen atomn = 1: −2.18 × 10⁻¹⁸ J; n = 2: −5.45 × 10⁻¹⁹ J; n = 3: −2.42 × 10⁻¹⁹ J; n = 4: −1.36 × 10⁻¹⁹ J; n = 5: −8.72 × 10⁻²⁰ J. Arrow from n = 1 to n = 2 (absorption).n = ∞0 Jn = 1−2.18 × 10⁻¹⁸ Jn = 2−5.45 × 10⁻¹⁹ Jn = 3−2.42 × 10⁻¹⁹ Jn = 4−1.36 × 10⁻¹⁹ Jn = 5−8.72 × 10⁻²⁰ Jabsorption

n=1→2n = 1 \to 2 absorbs at 122 nm (UV).

Example

Cool hydrogen has almost every atom in n=1n = 1, so it absorbs only Lyman lines: 122, 103 and 97 nm, all in the UV.

See alsoEmission spectrumLine spectrumGround stateLyman series