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.

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.

Explain the relationship between ionization energy and Coulomb's law.

Rank the elements Be, B, and Li in order of increasing first ionization energy. Justify your answer.

Compare the sizes of a Cl⁻ ion and a K⁺ ion, and explain the factors that contribute to the difference.

Predict whether the trend in ionic radii is consistent across a period for anions and cations. Justify your answer.

i) A new element X is found in Group 2, Period 5. Predict its ion charge and typical compound type when reacting with fluorine.

ii) Determine, with a reason, whether the percentage of ionic character is higher or lower in the compound formed in part i) compared to magnesium fluoride.

Compare the expected first ionization energy of element X with that of magnesium. Justify your answer based on periodic trends.