AP Chemistry Practice Quiz: Valence Electrons and Ionic Compounds
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
All Questions (10)
A) KBr
B) K2Br
C) KBr2
D) K2Br3
Correct Answer: A
According to the principle that elements in the same column of the periodic table tend to form analogous compounds, potassium (K) will behave similarly to sodium (Na), and bromine (Br) will behave similarly to chlorine (Cl). Therefore, the compound they form will have a 1:1 ratio, just like NaCl, resulting in the formula KBr.
A) 1+
B) 2+
C) 1-
D) 2-
Correct Answer: D
Elements in Group 16 have 6 valence electrons. To achieve a stable electron configuration (an octet), they tend to gain 2 electrons. Gaining 2 negatively charged electrons results in an ion with a charge of 2-.
A) The total number of protons in both atoms.
B) The interactions between the core electrons of the atoms.
C) The interactions between the valence electrons and the nuclei of the atoms.
D) The total mass of the two reacting atoms.
Correct Answer: C
The provided content explicitly states that the likelihood of chemical bond formation is determined by the interactions between the valence electrons and nuclei of the atoms involved. These outermost electrons are the ones that participate in bonding.
A) They have a large number of protons, which attracts other elements.
B) They have a single valence electron that is readily lost to form a stable cation.
C) They are gases at room temperature, which increases their kinetic energy.
D) They have filled d-orbitals that participate in bonding.
Correct Answer: B
The relationship between reactivity and periodicity is based on electron configuration. Alkali metals are in Group 1 and all have one valence electron. Their chemical reactivity is characterized by the tendency to lose this single electron to achieve a stable, noble-gas electron configuration, forming a +1 ion.
A) CaCl
B) Ca2Cl
C) CaCl2
D) Ca2Cl3
Correct Answer: C
The charge of an ion is predicted by its location on the periodic table. Calcium (Group 2) has two valence electrons and will lose them to form a Ca²⁺ ion. Chlorine (Group 17) has seven valence electrons and will gain one to form a Cl⁻ ion. To create a neutral compound, one Ca²⁺ ion is needed to balance two Cl⁻ ions, resulting in the formula CaCl₂.
A) Sulfur is heavier than oxygen, so it will form a compound with a different ratio, likely NaS.
B) Since sulfur is in the same column as oxygen, it has the same number of valence electrons, forms a similar ion (S²⁻), and will form an analogous compound, Na₂S.
C) Sodium and sulfur are in different periods, so they cannot form a compound with the same ratio as sodium and oxygen.
D) The reactivity of sulfur is much lower than oxygen, preventing the formation of a stable compound with sodium.
Correct Answer: B
The principle of periodicity states that elements in the same column tend to form analogous compounds because they have the same number of valence electrons and thus form ions with the same charge. Since S is in the same column (Group 16) as O, it will also form a 2- ion, leading to the formula Na₂S.
A) Group 1
B) Group 2
C) Group 13
D) Group 17
Correct Answer: B
Nitrogen (Group 15) typically forms a 3- ion (N³⁻). In the compound X₃N₂, the total negative charge from two nitrogen ions is 2 * (-3) = -6. To balance this, the total positive charge from three X ions must be +6. Therefore, each X ion must have a charge of +2 (X²⁺). Elements that typically form +2 ions have two valence electrons and are located in Group 2.
A) All elements become less reactive as atomic number increases.
B) The reactivity of elements is directly proportional to their atomic mass.
C) The chemical properties of elements, such as reactivity, show periodic trends related to their valence electron configurations.
D) Elements in the same column have identical, not just similar, chemical properties.
Correct Answer: C
This illustrates the direct relationship between trends in reactivity and periodicity. The way reactivity changes (increasing for metals, decreasing for nonmetals down a group) is a predictable pattern based on how valence electron interactions with the nucleus change with atomic size, which is a key aspect of periodicity.
A) Lithium and Oxygen
B) Magnesium and Fluorine
C) Potassium and Chlorine
D) Aluminum and Sulfur
Correct Answer: C
A 1:1 ratio occurs when the cation and anion have equal and opposite charges (e.g., +1 and -1, or +2 and -2). Potassium (K, Group 1) forms a K⁺ ion. Chlorine (Cl, Group 17) forms a Cl⁻ ion. These combine in a 1:1 ratio to form KCl. The other pairs would form Li₂O, MgF₂, and Al₂S₃.
A) Both Cs and F have a similar number of valence electrons, which promotes sharing.
B) Cesium's single valence electron is weakly held far from its nucleus, while fluorine's nucleus has a strong attraction for an additional electron in its nearby valence shell.
C) The core electrons of cesium and fluorine are arranged in a way that creates a strong magnetic attraction between the two atoms.
D) Cesium and fluorine are both highly reactive, and any two highly reactive elements will form a strong ionic bond.
Correct Answer: B
This question combines multiple concepts. Bond formation is driven by valence electron-nucleus interactions. Cesium (a large Group 1 atom) has one valence electron that is very far from the nucleus and easily removed. Fluorine (a small Group 17 atom) has a strong nuclear charge that is very effective at attracting a new electron into its close-by valence shell. This large difference in the tendency to lose vs. gain an electron makes ionic bond formation extremely likely.