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

43 mins16 questions
1a
1 point

Explain why atomic radius decreases across a period.

1b
1 point

Predict which element has the smaller atomic radius: Mg or Al. Justify your answer based on periodic trends.

1c
2 points

Sodium and chlorine are in the same period. Compare their atomic radii and explain the difference.

2a
1 point

Define ionic radius

2b
2 points

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

2c
1 point

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

1a
1 point

Define first ionization energy.

1b
2 points

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

1c
1 point


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

2a
1 point

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.

2b
2 points

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.

2c
2 points

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.

2d
2 points

A student proposes the following isoelectronic series: O2-, F-, Na+, Mg2+.

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

2e
2 points

Magnesium and nitrogen form the ionic compound Mg3N2.
Compare the relative ionic radii of the Mg2+ and N3- ions, and justify your answer using concepts of effective nuclear charge and electron configuration.

2f
1 point

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

3a
2 points

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

3b
2 points

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

1a
2 points

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

1b
2 points

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

2a
3 points

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.

2b
1 point

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