CIE A Level Physics (9702) 2019-2021

Revision Notes

27.3.1 Atomic Energy Levels

Atomic Energy Levels

  • Electrons in an atom can have only certain specific energies
    • These energies are called electron energy levels
  • They can be represented as a series of stacked horizontal lines increasing in energy
  • Normally, electrons occupy the lowest energy level available, this is known as the ground state
  • Electrons can gain energy and move up the energy levels if it absorbs energy either by:
    • Collisions with other atoms or electrons
    • Absorbing a photon
    • A physical source, such as heat
  • This is known as excitation, and when electrons move up an energy level, they are said to be in an excited state
  • If the electron gains enough energy to be removed from the atom entirely, this is known as ionisation
  • When an electron returns to a lower energy state from a higher excited state, it releases energy in the form of a photon

Electron energy levels in atomic hydrogen. Photons are emitted when an electron moves from a higher energy state to a lower energy state

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