Periodic Trends (College Board AP® Chemistry): Exam Questions

Define first ionization energy.

Compare the first ionization energies of Li and Na. Justify your answer using effective nuclear charge and electron shielding.

Explain why the first ionization energy of oxygen is slightly lower than that of nitrogen, despite the general trend.

Define ionic radius

Predict whether a Mg²⁺ ion or a Na⁺ ion will have a smaller ionic radius and justify your answer.

Explain how the ionic radius changes when sulfur forms an anion.

A materials scientist is studying elements across Period 3 to evaluate their suitability for use in safe flame-retardant compounds. The scientist is particularly interested in the relationships between atomic structure and chemical behavior for elements from sodium to chlorine.

The atomic radii of Na, Mg, and Al decrease across Period 3. Explain this trend using nuclear charge and electron shielding.

Chlorine and iodine are both Group 17 elements.

Predict which of the two has a greater first ionization energy, and justify your prediction using Coulomb’s Law and periodic position.

The electron affinity of chlorine is more negative than that of fluorine, even though fluorine is more electronegative. Explain this anomaly using atomic structure and electron repulsion.

A student proposes the following isoelectronic series: O^2-, F^-, Na⁺, Mg²⁺.

Rank the species in order of increasing ionic radius, and justify your reasoning using effective nuclear charge.

Magnesium and nitrogen form the ionic compound Mg₃N₂.
Compare the relative ionic radii of the Mg²⁺ and N^3- ions, and justify your answer using concepts of effective nuclear charge and electron configuration.

Predict whether sodium or phosphorus is more likely to form a basic oxide. Justify your answer.