E.1.4—Atomic transitions

Emission

When an electron moves from a higher atomic energy level to a lower one, the atom emits one photon. The photon energy equals the level difference: $E_\gamma=\Delta E$ .

Absorption

An atom can absorb a photon only when its energy matches an allowed upward transition. The electron then moves to the higher level, so the spectrum records the same allowed energy differences in reverse.

Read a transition diagram

For each downward arrow, calculate the energy gap between its initial and final levels. A larger gap produces a higher-frequency photon and a shorter wavelength; a smaller gap produces a lower-frequency photon and a longer wavelength.

Common trap

Do not use the absolute energy of one level as the photon energy. A photon is associated with the difference between two levels, and emission requires a downward transition.

How it is assessed

Questions use energy-level diagrams to select transitions and compare photon wavelength, frequency or number of spectral lines.

Command terms

Calculate / Identify

What earns marks

Identify the relevant energy gap first, then use the inverse relation between photon energy and wavelength when needed. Count only transitions represented by the diagram.

Watch for

Choosing the largest absolute level value rather than the largest energy difference, or treating wavelength as directly proportional to photon energy.

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 $E_\gamma=hf=hc/\lambda$ 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.

E.1.4—Atomic transitions

Model Atomic Transitions

E.1.4 Exam Analysis

Assessment in practice

Retrieve the SL Atomic Model