Paper 2 · periodicity and ionisation energy
Fig. 1 shows the first ionisation energies of the elements sodium to argon. The value for aluminium is lower than that for magnesium because the electron removed from aluminium
Acomes from a 3p orbital, which is higher in energy than the 3s
Bcomes from a completely filled 3s orbital
Cexperiences a greater nuclear charge
Dis closer to the nucleus
Explanation: The 3p electron of aluminium is slightly further from the nucleus and better shielded, so it is easier to remove.
Derived from ZIMSEC Chemistry Paper 2, June 2014, Q1
