CIE AS Chemistry (9701) exams from 2022

Revision Notes

1.1.10 Ionisation Energy

First Ionisation Energy

  • The ionisation energy (IE) of an element is the amount of energy required to remove one mole of electrons from one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
  • Ionisation energies are measured under standard conditions which are 298 K and 1 atm
  • The units of IE are kilojoules per mole (kJ mol-1)
  • The first ionisation energy (IE1) is the energy required to remove the first electron from an atom of an element
    • Eg. the first ionisation energy of gaseous calcium:

Ca(g) → Ca+ (g) + e          IE1 = 590 kJ mol-1

Ionisation Energies: Equations

  • The second ionisation energy (IE2) is the energy required to remove the second electron from each ion in a mole of gaseous +1 ions
  • The third ionisation energy (IE3) is the energy required to remove the third electron from each ion in a mole of gaseous +2 ions
  • The electrons from an atom can be continued to be removed until only the nucleus is left
  • This sequence of ionisation energies is called successive ionisation energies

Successive ionisation energies of Beryllium table

Atomic Structure Table 1_Successive ionisation energies of Beryllium, downloadable AS & A Level Chemistry revision notes

Exam Tip

Remember that equations to represent ionisation energies must have gaseous (g) state symbols for the atoms and ions but not for the electrons.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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