CART - Chemistry Acceleration Readiness Chemical Bonding and Nomenclature Questions and Answers — Questions and Answers

Question 1: Which of the following compounds requires a Roman numeral in its name?

FeCl₃ (Correct answer)
BaCl₂
Al₂O₃
Na₂S

Correct answer: FeCl₃

Iron (Fe) is a transition metal that can form multiple stable ions (Fe²⁺ and Fe³⁺). Therefore, a Roman numeral is required to specify the charge of the iron cation in the compound. In FeCl₃, chlorine has a charge of -1, and since there are three chlorine atoms, the total negative charge is -3. To balance this, the iron ion must have a charge of +3, so the correct name is Iron(III) Chloride. Barium, aluminum, and sodium are main group metals that form ions with only one predictable charge (Ba²⁺, Al³⁺, and Na⁺ respectively), so no Roman numeral is needed for them.

Question 2: A chemist is analyzing a substance and finds that it is composed of atoms that share electrons to form discrete molecules. The electronegativity difference between the bonded atoms is 1.2. How should this substance's bonding be classified?

Ionic
Polar covalent (Correct answer)
Nonpolar covalent
Metallic

Correct answer: Polar covalent

The type of bond between two atoms can be predicted by their electronegativity difference. A difference between approximately 0.4 and 1.7 indicates a polar covalent bond, where electrons are shared unequally, creating partial positive and negative charges. An electronegativity difference greater than 1.7 typically results in an ionic bond, while a difference less than 0.4 results in a nonpolar covalent bond. Metallic bonding involves a 'sea' of delocalized electrons and is not determined by this metric.

Question 3: What is the correct chemical formula for the ionic compound formed between magnesium and the phosphate polyatomic ion?

MgPO₄
Mg₂(PO₄)₃
Mg₃(PO₄)₂ (Correct answer)
Mg(PO₄)₂

Correct answer: Mg₃(PO₄)₂

Magnesium (Mg), an alkaline earth metal in Group 2, forms a cation with a +2 charge (Mg²⁺). The phosphate polyatomic ion has the formula PO₄³⁻ and a charge of -3. To form a neutral compound, the total positive charge must equal the total negative charge. The least common multiple of 2 and 3 is 6. Therefore, three Mg²⁺ ions (3 x +2 = +6) are needed to balance two PO₄³⁻ ions (2 x -3 = -6). The correct formula is Mg₃(PO₄)₂.

Question 4: Which of the following correctly names the covalent compound N₂O₅?

Nitrogen oxide
Dinitrogen pentoxide (Correct answer)
Nitrogen(V) oxide
Dinitrogen oxide

Correct answer: Dinitrogen pentoxide

For binary covalent compounds (compounds between two nonmetals), Greek prefixes are used to indicate the number of each type of atom. The prefix for two is 'di-' and the prefix for five is 'penta-'. Therefore, N₂O₅ is named dinitrogen pentoxide. The other names are incorrect because they either omit the prefixes or use the stock system (Roman numerals), which is reserved for ionic compounds with variable-charge metals.

Question 5: According to VSEPR theory, what is the molecular geometry of a molecule with a central atom that has two bonding pairs and two lone pairs of electrons?

Linear
Tetrahedral
Trigonal pyramidal
Bent (Correct answer)

Correct answer: Bent

Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shape based on minimizing repulsion between electron pairs. A central atom with four electron domains (two bonding pairs and two lone pairs) has a tetrahedral electron geometry. However, the molecular geometry is determined only by the positions of the atoms. The two lone pairs repel the bonding pairs more strongly, pushing the bonded atoms closer together and resulting in a bent or angular molecular shape, like in a water molecule (H₂O).

Question 6: What is the name of the polyatomic ion with the formula ClO₂⁻?

Perchlorate
Chlorate
Chlorite (Correct answer)
Hypochlorite

Correct answer: Chlorite

This question requires knowledge of the nomenclature for polyatomic oxyanions. The series of chlorine-oxygen anions follows a pattern. ClO₄⁻ is perchlorate, ClO₃⁻ is chlorate, ClO₂⁻ is chlorite, and ClO⁻ is hypochlorite. The '-ate' suffix is used for the ion with more oxygen atoms, and the '-ite' suffix for the ion with fewer oxygen atoms. The 'per-' prefix indicates one more oxygen than the '-ate' ion, and the 'hypo-' prefix indicates one less oxygen than the '-ite' ion.

CART - Chemistry Acceleration Readiness Chemical Bonding and Nomenclature Questions and Answers

Which of the following compounds requires a Roman numeral in its name?