Ionisation Energy & Electronic Configuration (Cambridge (CIE) AS Chemistry): Revision Note

Ionisation Energies: Electronic Configuration

Using Successive Ionisation Energy Data

• Each ionisation energy refers to the energy required to remove one one mole of electrons from one mole of a specific species in the gaseous state

  • First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms

  • Successive ionisation energies are the energy required to remove one mole of electrons from one mole of gaseous positive ions

• As electrons are removed, the ion becomes more positively charged

  • This increases the electrostatic attraction between the nucleus and remaining electrons

  • Therefore, ionisation energies increase progressively

• A large jump in successive ionisation energies indicates that:

  • An electron is being removed from a new, inner shell closer to the nucleus

  • These electrons experience a stronger attraction to the nucleus and require more energy to remove

How to deduce electronic configuration

• Look for the largest increase between two successive ionisation energies

• The number of electrons removed before this jump = number of outer-shell (valence) electrons

• This corresponds to the element’s group number in the Periodic Table (for s- and p-block elements)