Ionisation Energy

Ionisation Energy

1. The first ionisation energy is the energy required to remove the least tightly held electron from each atom in one mole of gaseous atoms in their ground state (e.g. Na(g) -> Na+(g) + 1e-)

   • The second and third ionisation energies are the energies needed to remove the second and third electrons, respectively
     • Ionisation energies are all positive values, as the breaking of the electrostatic attraction between a valence electron and the nucleus must be an endothermic process

2. Across a period there is an increase in ionisation energy due to the increase in electrostatic attraction between the nucleus and valence electron - there is an increase in nuclear charge, but electrons are added into the same energy level with no additional shielding

3. Down a group ionisation energy decreases due to the decrease in electrostatic attraction between nucleus and valence electron - although there is an increase in nuclear charge, electrons are being added to higher energy levels further from the nucleus with additional shielding from inner shells of electrons