Magnesium and aluminum are adjacent elements in Period 3
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
Magnesium and aluminum are adjacent elements in Period 3. Portions of their successive ionization energies are listed below.
1st IE (kJ mol⁻¹) 2nd IE (kJ mol⁻¹) 3rd IE (kJ mol⁻¹)
Mg 738 1451 7733
Al 578 1817 2745
Use the data to answer the following questions about their electronic structures and periodic behavior.
(a) Calculate the ratio 2nd IE3rd IE for each element and describe what the magnitude of this ratio indicates about the relative difficulty of removing the third electron.
(b) Identify which of the two elements shows evidence of having completed a filled subshell after removal of its first two electrons, and cite the data that support your conclusion.
(c) Explain, in terms of electron configuration and effective nuclear charge, why the third ionization energy of magnesium is dramatically larger than that of aluminum despite magnesium’s lower nuclear charge.
(d) Predict which element would exhibit a larger fourth ionization energy and justify your answer without performing a numerical calculation.