Consider a dual-axis graph that simultaneously displays atomic radius (left y-axis
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
Consider a dual-axis graph that simultaneously displays atomic radius (left y-axis, in picometers) and first-ionization energy (right y-axis, in kJ·mol⁻¹) for the eight elements of Period 3 (Na to Ar) as a function of atomic number. The atomic-radius curve decreases fairly smoothly from Na to Ar, whereas the ionization-energy curve increases overall but features small downturns at Mg→Al and P→S.
Respond to the prompts below.
(a) Using the qualitative trends described, explain why an inverse relationship exists between atomic radius and first-ionization energy across a single period.
(b) Provide an electron-configuration–based rationale for each of the two local downturns observed in the ionization-energy curve.
(c) Identify the Period 3 element whose measured first-ionization energy deviates most negatively from the smooth rising trend predicted by simple Coulombic attraction alone, and justify your choice.