CIE A Level Physics复习笔记22.3.1 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