Edexcel International AS Chemistry

Revision Notes

2.4.1 Ionisation Energy - Groups 1 & 2

Ionisation Energy Trends

  • All elements in Groups 1 (also called alkali metals) have one electron in their outermost principal quantum shell
  • All elements in Groups 2 (also called alkali earth metals) have two electrons in their outermost principal quantum shell
  • All Group 1 and Group 2 metals can form ionic compounds in which they donate these outermost electrons (so they act as reducing agents) to become an ion with either a +1 or +2 charge (so they themselves become oxidised)
  • Going down the group, the metals become more reactive
    • This can be explained by looking at the Group 2 ionisation energies:

Group 2 - Ionisation Energy Group 2 Elements, downloadable AS & A Level Chemistry revision notes

The graph shows that both the first and second ionization energies decrease going down the group

  • The same trend is observed with Group 1 alkali metalsĀ 
  • The first ionisation energy is the energy needed to remove the first outer electron of an atom
  • The second ionisation energy is the energy needed to remove the second outer electron of an atom
  • The graph above shows that going down the group, it becomes easier to remove the outer two electrons of the metals
  • Though the nuclear charge increases going down the group (because there are more protons), factors such as an increased shielding effect and a larger distance between the outermost electrons and nucleus outweigh the attraction of the higher nuclear charge

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