Atomic Energy Levels (Cambridge (CIE) A Level Physics): Revision Note

Atomic energy levels

• Electrons in an atom can have only certain specific (discrete) 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 they absorb energy 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