E.1.3—Atomic energy levels
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- SL
Read Spectral Evidence
Emission lines
An excited gas emits light at particular frequencies, producing bright spectral lines rather than a continuous spread of frequencies. Each line corresponds to a permitted energy difference between atomic states.
Absorption lines
When continuous light passes through a cooler gas, the atoms remove the same frequencies they can emit. The resulting dark lines therefore occur at specific, repeatable wavelengths.
Infer discrete levels
Because only particular photon energies are emitted or absorbed, the atom’s energy states are discrete rather than continuous. The spectrum is evidence for quantized atomic energy levels.
Common trap
Do not treat every visible line as a separate element without considering transitions. A spectrum is evidence of allowed energy differences; the pattern, not simply the number of lines, carries the information.
E.1.3 Exam Analysis
Assessment in practice
1–2 marksHow it is assessed
Questions count possible photon-emitting transitions or distinguish what spectra reveal about atoms.
Command terms
State / Identify
What earns marks
Count only allowed downward transitions for emission, and identify discrete atomic energy levels—not mass-energy equivalence—as the inference from line spectra.
Watch for
Counting energy levels instead of allowed transitions or claiming that line spectra directly provide evidence for mass-energy equivalence.
Retrieve the SL Atomic Model
Retrieve the evidence chain
Rutherford scattering supports a small positive nucleus; nuclear notation separates protons, neutrons and electrons; line spectra show discrete energy differences; and Eγ=hf=hc/λ connects transitions to photons.
Check the model
When reading a spectrum, identify the transition, use the energy difference rather than an absolute level, and compare characteristic lines with known spectra to identify elements.