Atomic transitions and light emission

What you will learn

Discrete electron energies and emission of different light frequencies.

Specification mapping: A1.3.1

Prerequisites: A1.1.1

Physical principles

An atom has allowed electron energy states. Energy absorbed from a discharge or flame can excite an electron to a higher state. When it drops to a lower allowed state, the atom can emit a photon carrying the energy difference. The lower state need not be the ground state.

Because allowed differences are discrete, emitted photons have particular frequencies. A larger downward energy difference produces a higher frequency and shorter vacuum wavelength. The supporting relation ΔE = hf links photon energy to frequency; h is Planck’s constant. It explains the mechanism rather than adding an unlisted Unit 3 calculation requirement.

A collection of atoms can produce several lines because different transitions are possible. A line spectrum is not a continuous rainbow: missing frequencies reflect unavailable transitions. Some transitions lie outside the visible region, so a visible spectrum alone may show only part of an element’s emission.

Scientific diagram and interpretation

Equations and relationships

ΔE = hf (supporting explanation)

Worked examples and applications

Common misconceptions

Electrons emit photons on downward transitions, not simply because they orbit an atom.

Examination technique

Describe excitation, a lower final state, and energy conservation in that order.

For an explanation, connect the physical cause to its effect. For a calculation, state the model, rearrange before substitution, retain intermediate digits, and finish with units. For a data question, refer to the actual readings and distinguish a trend from proof of a cause.

Check your understanding

Five questions. Choose an option, then Check Answer. Read the feedback and use Try Again to reset. Use Tab between controls, arrow keys within radio groups, and Enter or Space on buttons. These local practice answers are not saved.