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AP Chemistry Practice Quiz: Periodic Trends

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

The organization of the modern periodic table is based on the recurring nature of elemental properties. This periodicity is most directly explained by patterns in which of the following?

All Questions (10)

The organization of the modern periodic table is based on the recurring nature of elemental properties. This periodicity is most directly explained by patterns in which of the following?

A) The number of neutrons in the nucleus

B) The atomic mass of the elements

C) The ground-state electron configurations of the elements

D) The physical state of the elements at standard conditions

Correct Answer: C

The provided content states that the periodic table's organization is based on recurring properties which are explained by 'patterns of ground-state electron configurations and filled/partially filled shells.'

Which of the following best explains why the atomic radius decreases from left to right across a period?

A) The number of principal energy shells increases, pulling electrons further from the nucleus.

B) The effective nuclear charge increases for electrons in the same shell, increasing the attraction to the nucleus.

C) The shielding effect of the core electrons increases, reducing the attraction between the nucleus and valence electrons.

D) The mass of the nucleus increases, causing the atom to contract.

Correct Answer: B

Across a period, protons are added to the nucleus while electrons are added to the same principal energy shell. This increases the effective nuclear charge (Zeff), which, according to Coulomb's law, results in a stronger attraction that pulls the electron cloud closer to the nucleus, decreasing the radius.

The first ionization energy of potassium (K) is less than the first ionization energy of sodium (Na). This observation is best attributed to the fact that the valence electron in potassium...

A) experiences a lower effective nuclear charge due to fewer protons.

B) is located in a higher principal energy level and experiences greater shielding.

C) is part of a more stable, partially filled d-orbital.

D) is more strongly attracted to the nucleus according to Coulomb's law.

Correct Answer: B

Potassium's valence electron is in the n=4 shell, while sodium's is in the n=3 shell. According to the shell model, the electron in potassium is further from the nucleus and is more effectively shielded by the inner-shell electrons. This increased distance and shielding weakens the electrostatic attraction (Coulomb's law), making the electron easier to remove.

A scientist needs to estimate the electronegativity of a newly discovered element but lacks the experimental data to measure it directly. Which of the following principles is most useful for making a qualitative prediction?

A) The law of conservation of energy

B) The concept of periodicity and the element's position on the table

C) The law of definite proportions

D) The average atomic mass of known isotopes

Correct Answer: B

The provided content explicitly states, 'Periodicity is useful to predict/estimate values of properties in the absence of data.' By knowing the element's position, one can use established trends to estimate its electronegativity.

The periodic trends for properties such as ionization energy and atomic radius are qualitatively understood using several key concepts. Which concept describes the reduction of the full attractive force of the nucleus on valence electrons due to the presence of inner-shell electrons?

A) Effective nuclear charge

B) Electronegativity

C) The shell model

D) Shielding

Correct Answer: D

Shielding is the effect where inner-shell electrons repel the outer-shell (valence) electrons, partially canceling out the attractive force of the positive nucleus. This reduces the net positive charge experienced by the valence electrons.

According to Coulomb's law and the principles of periodic trends, which of the following factors is most responsible for the general increase in first ionization energy from left to right across period 2?

A) The increase in the number of valence electrons.

B) The increase in the number of core electrons.

C) The increase in effective nuclear charge.

D) The decrease in electron affinity.

Correct Answer: C

Moving across a period, the number of protons in the nucleus increases, while electrons are added to the same energy shell. This leads to a greater effective nuclear charge (Zeff), which increases the Coulombic attraction between the nucleus and the valence electrons, thus requiring more energy to remove one (higher ionization energy).

The radius of a magnesium ion, Mg²⁺, is significantly smaller than the radius of a neutral magnesium atom, Mg. Which of the following provides the best explanation for this difference?

A) The Mg²⁺ ion has fewer protons than the Mg atom.

B) The removal of two electrons eliminates the outermost electron shell.

C) The Mg²⁺ ion has more neutrons, which causes the nucleus to contract.

D) The addition of two electrons increases electron-electron repulsion.

Correct Answer: B

A neutral Mg atom has an electron configuration of [Ne]3s². To form the Mg²⁺ ion, both 3s electrons are removed. This completely removes the n=3 shell, meaning the new valence shell is the much smaller n=2 shell. This loss of an entire shell results in a dramatic decrease in radius.

The fundamental connection between an element's position in the periodic table and its properties, such as atomic radius and ionization energy, is best described as a relationship between these properties and the element's...

A) atomic mass.

B) electronic structure.

C) nuclear density.

D) isotopic stability.

Correct Answer: B

The first point in the provided content explicitly states the need to 'Explain the relationship between trends in atomic properties of elements and electronic structure and periodicity.' The electronic structure, particularly the valence electron configuration, dictates an element's chemical properties and its position on the table.

Consider the elements Si, P, S, and Cl. The trend of increasing electronegativity across this series can be primarily attributed to an increase in the effective nuclear charge (Zeff). This increased Zeff leads to...

A) a weaker Coulombic attraction for bonding electrons due to increased shielding.

B) a stronger Coulombic attraction for bonding electrons as the nuclear charge increases and atomic radius decreases.

C) the addition of an electron to a new, higher-energy shell, which is held less tightly.

D) a decrease in the number of valence electrons, reducing electron-electron repulsion.

Correct Answer: B

As you move from Si to Cl across the period, the number of protons increases, leading to a higher Zeff. According to Coulomb's law, a greater charge (Zeff) and a smaller distance (decreasing atomic radius) result in a stronger force of attraction. For electronegativity, this means a stronger attraction for electrons in a chemical bond.

The shell model is essential for explaining why ionization energy decreases down a group. The primary reason for this trend is that as you move down a group...

A) the effective nuclear charge decreases, weakening the attraction for valence electrons.

B) the number of valence electrons increases, leading to greater electron-electron repulsion.

C) each successive element has its valence electrons in a higher principal energy level, further from the nucleus.

D) the nucleus becomes less dense, reducing its overall attractive force.

Correct Answer: C

The shell model posits that electrons exist in discrete energy levels (shells). Moving down a group, the principal quantum number (n) of the valence shell increases. This means the outermost electrons are physically further from the nucleus, which, combined with increased shielding, weakens the Coulombic attraction and lowers the ionization energy.