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CHEMISTRY, M1 EQ-Bank 6

Describe the process by which emission line spectra are formed.   (4 marks)

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  • Electrons in atoms exist in discrete energy levels.
  • When an atom absorbs energy (e.g. from heat or electricity), an electron is excited to a higher energy level.
  • The excited electron is unstable and will eventually fall back to a lower energy level.
  • As it does so, it releases energy in the form of a photon of light.
  • The energy of the photon corresponds to the difference between the two energy levels, so only specific wavelengths of light are emitted.
  • Passing this light through a spectroscope produces a series of discrete coloured lines known as the emission spectrum.
Show Worked Solution
  • Electrons in atoms exist in discrete energy levels.
  • When an atom absorbs energy (e.g. from heat or electricity), an electron is excited to a higher energy level.
  • The excited electron is unstable and will eventually fall back to a lower energy level.
  • As it does so, it releases energy in the form of a photon of light.
  • The energy of the photon corresponds to the difference between the two energy levels, so only specific wavelengths of light are emitted.
  • Passing this light through a spectroscope produces a series of discrete coloured lines known as the emission spectrum.

CHEMISTRY, M1 2013 HSC 35a

The emission spectrum of a metal salt is observed with a spectroscope. 

Explain the processes by which emission lines arise. Include an energy level diagram for the lines marked A and B in your response.   (3 marks)

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  • Metal ions absorb flame energy which causes electrons to jump to higher energy levels.
  • Subsequently, excited electrons fall back to lower levels. This process releases specific amounts of energy as light photons.
  • Since electron energies are quantised and transitions between states are restricted to well-defined energies, the energy released is well defined. 
  • In the spectroscope image, each line represents one specific electron transition.
  • Line A is the blue end of the spectrum, meaning the transition is of high energy (shorter wavelength).
  • Line B is at the red end of the spectrum, meaning the transition is of low energy (longer wavelength).
  • This demonstrates why emission spectra show distinct coloured lines.
Show Worked Solution
  • Metal ions absorb flame energy which causes electrons to jump to higher energy levels.
  • Subsequently, excited electrons fall back to lower levels. This process releases specific amounts of energy as light photons.
  • Since electron energies are quantised and transitions between states are restricted to well-defined energies, the energy released is well defined. 
  • In the spectroscope image, each line represents one specific electron transition.
  • Line A is the blue end of the spectrum, meaning the transition is of high energy (shorter wavelength).
  • Line B is at the red end of the spectrum, meaning the transition is of low energy (longer wavelength).
  • This demonstrates why emission spectra show distinct coloured lines.