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Photons

Ionisation energy from an energy level diagram

  • 3 things to know
  • Component 3

Overview

Ionisation energy of an atom and convergence limit of a line spectrum.

What you need to know

Answer each one before you reveal it.

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Key term

An atom has a ground state at −13.6 eV. State its ionisation energy.

Key term

Convert an ionisation energy of 13.6 eV into joules

Key term

What is the ionisation energy measured from if the electron is already in an excited state?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define the ionisation energy of an atom.

    Model answer

    The ionisation energy is the energy needed to remove an electron completely from the atom, taking it from the ground state to the free state.

  2. 2

    How is the ionisation energy read from an energy level diagram?

    Model answer

    It is the magnitude of the energy of the ground state, since the free state is taken as zero.

  3. 3

    An atom has a ground state at −13.6 eV. State its ionisation energy.

    Model answer

    13.6 eV, the energy needed to raise the electron from −13.6 eV to zero.

  4. 4

    Convert that ionisation energy into joules.

    Model answer

    13.6 × 1.60 × 10⁻¹⁹, which is 2.18 × 10⁻¹⁸ J.

  5. 5

    What is the ionisation energy measured from if the electron is already in an excited state?

    Model answer

    From that excited level, so it is the magnitude of that level's energy and is smaller than from the ground state.

  6. 6

    An atom has an excited state at −3.4 eV. What energy is needed to ionise it from there?

    Model answer

    3.4 eV.

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