What evidence do line spectra provide about the energy of electrons in atoms?

Line spectra provide evidence that electrons in atoms can only occupy discrete energy levels, not a continuous range of energies.

Why do line spectra consist of distinct lines rather than a continuous band of colours?

Because electrons can only exist at specific, discrete energy levels, so only photons with specific energies (corresponding to transitions between these levels) are emitted or absorbed.

What happens to energy when an electron transitions from a higher to a lower energy level in an atom?

A photon is emitted with energy exactly equal to the difference between the two energy levels.

What must occur for an electron to move from a lower to a higher energy level?

The electron must absorb a photon with energy exactly equal to the difference between the two energy levels.

State the equation relating photon energy to the energy levels involved in an electron transition.

hf = E₁ − E₂, where h is the Planck constant, f is the photon frequency, and E₁ and E₂ are the energies of the two levels.

In the equation hf = E₁ − E₂, what does each symbol represent?

h is the Planck constant, f is the frequency of the emitted or absorbed photon, and E₁ and E₂ are the energies of the initial and final energy levels respectively.

AQA A-Level Physics 7408

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Particles and Radiation

Energy levels and photon emission

5 things to know
Papers 1 and 3

Overview

Discrete energy levels, emission and absorption line spectra, and the diffraction grating.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

In what units are energy levels given, and how is photon frequency found from them?

Key term

How is an absorption line spectrum produced, and how does it look beside an emission spectrum?

Key term

How is a diffraction grating used to observe line spectra, and what is the ground state?

Key term

What are excited states in an atom?

Process

What happens to the wavelength of an emitted photon as the energy difference between levels increases?

Questions from this subtopic

Each one with the model answer underneath.

1
What evidence do line spectra provide about the energy of electrons in atoms?
Model answer
Line spectra provide evidence that electrons in atoms can only occupy discrete energy levels, not a continuous range of energies.
2
Why do line spectra consist of distinct lines rather than a continuous band of colours?
Model answer
Because electrons can only exist at specific, discrete energy levels, so only photons with specific energies (corresponding to transitions between these levels) are emitted or absorbed.
3
What happens to energy when an electron transitions from a higher to a lower energy level in an atom?
Model answer
A photon is emitted with energy exactly equal to the difference between the two energy levels.
4
What must occur for an electron to move from a lower to a higher energy level?
Model answer
The electron must absorb a photon with energy exactly equal to the difference between the two energy levels.
5
State the equation relating photon energy to the energy levels involved in an electron transition.
Model answer
hf = E₁ − E₂, where h is the Planck constant, f is the photon frequency, and E₁ and E₂ are the energies of the two levels.
6
In the equation hf = E₁ − E₂, what does each symbol represent?
Model answer
h is the Planck constant, f is the frequency of the emitted or absorbed photon, and E₁ and E₂ are the energies of the initial and final energy levels respectively.

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