Electron Energy Levels (OCR A Level Physics)

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Katie M


Katie M



Electron Energy Levels

  • A continuous spectrum is a spectrum that appears to contain all frequencies over a comparatively wide range
    • The Sun’s spectrum is not continuous as it shows dark lines where some frequencies are missing
  • Bohr explained the existence of spectral lines using the new photon model of electromagnetic radiation
  • In addition, Bohr proposed a model of the atom which includes:
    • Electrons orbiting the nucleus
    • Electrons only occupying specific orbits associated with a discrete set of energies
    • The orbits are also called shells or energy levels
    • Electrons can gain or lose energy by moving from one allowed energy level to another

4.1.1 Energy levels

Electrons in an atom can have only certain specific (discrete) energies within an atom

  • Energy is required for an electron to move from a lower to a higher energy level
    • This transition is called an excitation
  • Energy is released if the electron moves from a higher to a lower energy level
    • This transition is called a de–excitation
  • Electrons can move to a higher or lower energy level by absorbing or emitting electromagnetic radiation with a frequency, f
  • The energy required for excitation of a gas can be provided by:
    • A photon of a specific frequency
    • Energy absorbed from the surroundings (through heating)
    • Energy supplied by an electric field
  • The energy released during de–excitation is emitted as electromagnetic radiation of a specific frequency
    • This frequency depends on the difference of energy between the specific energy levels involved in the transition

Exam Tip

The values of energy level are all given using the unit electron volt (eV), because we are dealing with very small energy values. 1 eV is equal to 1.6 × 10–19 Joules, so to convert between J and eV, remember:

J space rightwards arrow with divided by 1.6 cross times 10 to the power of negative 19 end exponent on top space e V

e V space rightwards arrow with cross times 1.6 cross times 10 to the power of negative 19 end exponent on top space J

Negative Values of Energy Levels

  • The energy of an electron is taken to be zero when it is infinitely far from the nucleus
    • The forces of interaction between the electron and the nucleus are practically zero
    • Energy is regarded to be 0 eV and the electron is said to be free from the atom
  • Energy levels have negative values
  • Therefore, any energy value for an electron inside the atom will be negative
    • This is because external energy is required to remove an electron from its energy level
  • The negative values also mean that electrons are confined within the atom
  • The value of the energy level is equal to

The amount of energy required to remove an electron from that energy level

  • The energy level with the most negative value is the lowest energy level n = 1
    • This is called the ground state
  • The value for the energy level of the ground state is equal to

The energy required to remove an electron from the atom

  • For hydrogen, the energy value related to the ground state is equal to –13.6 eV
    • Hence, 13.6 eV is the energy required to remove an electron from the ground state of an atom of hydrogen
  • The complete removal of an electron from an atom is known as ionisation
    • If a photon of energy more than 13.6 eV is absorbed, then the excess energy after the electron has been ionised will be transferred to it as kinetic energy

Exam Tip

Electron energy levels are defined in a similar way to gravitational potential – when at infinity these quantities can be considered to be zero – this is to emphasise that when a mass is far away from another mass, the gravitational force no longer has an effect.

So, similarly, when the electron is far away from the nucleus, the electric force by the nucleus no longer has an effect on the electron.

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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