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Science

Spectroscopy and Atomic Spectra

Overview

Students explore how the light emitted by excited atoms reveals the discrete energy levels within atoms, connecting observable colour to the quantum nature of matter.

Learning Objective
Students understand how atomic emission spectra are produced and what they reveal about electron energy levels.

Resources needed

  • A diffraction grating or CD
  • A bright light source and salt or metal compounds for flame tests (if available)

Lesson stages

0 / 7 done
  1. 1 Ask: when you burn a piece of wood, why does it glow orange? When sodium burns, why is the flame yellow?
  2. 2 Introduce: different elements emit different colours of light — this is the basis of spectroscopy.
  3. 3 Perform flame tests if available: sodium gives yellow, copper gives green/blue, potassium gives lilac.
  4. 4 Introduce the concept: when an electron in an atom absorbs energy, it jumps to a higher energy level (excited state).
  5. 5 When it falls back down, it releases the energy as a photon of light. The energy difference determines the colour (wavelength) of the photon.
  6. 6 Since electrons can only occupy specific energy levels, only specific wavelengths of light are emitted — giving a unique line spectrum for each element.
  7. 7 Introduce: this is how astronomers identify the composition of stars — by analysing the light they emit.

Tap a step to mark it as done.

Variations

  • View a light source through a diffraction grating or CD — observe the spectrum.
  • Compare the spectra of different elements using a spectroscopy app or chart.
  • Discuss how hydrogen's line spectrum provided the first evidence for quantised energy levels.
More information

Teach: emission spectrum, line spectrum, energy level, photon, wavelength, frequency, quantised, excited state. The key concept: electrons can only have specific energies — they cannot have any energy in between. This is the quantum hypothesis.

Focus on the flame test observation and the energy level explanation before introducing line spectra and astronomical applications.

Can students explain why each element produces a unique line spectrum? Can they describe the process by which a photon is emitted when an electron falls from a higher to a lower energy level?

Flame tests require only a wire loop, water, different salts, and a flame — all very cheap. A CD or DVD surface acts as a diffraction grating to separate white light into its spectrum for free.

Students often think excited electrons stay permanently in their higher energy state. They return to the ground state almost immediately — the photon emission is essentially instantaneous. The excitement is transient, not stable.

Spectroscopy is one of the most powerful tools in science. It is used in chemistry (identifying substances), astronomy (determining star composition), medicine (blood analysis), and forensic science.

Activity details
Secondary Challenging 25 minutes no prep Whole Class, Small Group Indoor & Outdoor
Topics
Spectroscopy Atomic Spectra Quantum Theory