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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Emission spectrum

The bright lines given off when excited atoms drop to lower energy levels, each emitting a photon of energy ∣ΔE∣|\Delta E|. A hot or electrically excited gas shows bright lines on a dark background.

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 = 3 to n = 2 (emission).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 Jemission

n=3→2n = 3 \to 2 emits the red 656 nm line of hydrogen.

Example

Hydrogen atoms excited to n=4n = 4 can emit 4×32=6\tfrac{4 \times 3}{2} = 6 different lines on the way down to n=1n = 1: three Lyman, two Balmer and one Paschen.

See alsoAbsorption spectrumLine spectrumExcited stateEnergy level