AP Chemistry — Unit 2 Videos Quiz

Which of the following correctly indicates whether the solid represented by the particulate model shown above conducts electricity and explains why or why not?

C) It does not conduct electricity because its ions cannot move freely within the solid. Correct. In the solid state, the ions are held by strong coulombic forces in fixed positions within the lattice; thus they cannot move or migrate through the lattice. Related Videos 2.3: Daily Video 1

A particle-level diagram of a metallic element is shown above. Typically, metals are both malleable and ductile. The best explanation for these properties is that the electrons involved in bonding among metal atoms are

C) equally shared and form nondirectional bonds Correct. In metals, electrons are free to move as described by the electron sea model. Electrons are shared equally among atoms, and the structure is based on simple close-packed structures that contain no fixed directional bonds. Related Videos 2.4: Daily Video 1

Lewis diagrams of molecules of three different hydrocarbons are shown above. Which of the following claims about the molecules is best supported by the diagrams?

D) The strongest carbon-to-carbon bond occurs in molecule 3. Correct. Molecule 3 contains a triple bond between two carbon atoms. Between two of the same kind of atom, triple bonds are stronger than double bonds, which in turn are stronger than single bonds. Related Videos 2.7: Daily Video 1 2.7: Daily Video 2 2.7: Daily Video 3

The diagram above shows two resonance structures for a molecule of C6H6. The phenomenon shown in the diagram best supports which of the following claims about the bonding in C6H6 ?

A) In the C6H6 molecule, all the bonds between the carbon atoms have the same length. Correct. Because of resonance, all the bonds between carbon atoms in C6H6 are equivalent and have the same strength and equal lengths. Related Videos 2.6: Daily Video 1 2.6: Daily Video 2

The particle-level diagram above represents the structure of solid KF. Although the molar mass of KCl is greater than that of KF, the density of KCl is actually less than that of KF. Which of the following representations of the structure of KCl best helps to explain this phenomenon?

A) https://assets.learnosity.com/organisations/537/VH905919.g06.png Correct. The diagram shows that the chloride ions are larger than the fluoride ions, which causes the interionic distances in the solid to increase to the point where the effect of the larger spacing among ions in KCl is greater than the effect of the larger mass of the chlorine on the density. Related Videos 2.3: Daily Video 1

Which of the following Lewis diagrams best represents the bonding in the N2O molecule, considering formal charges?

B) https://assets.learnosity.com/organisations/537/VH903466.g02.png Correct. When the formal charge of each atom in this diagram is determined using the rule: (formal charge of an atom = the number of valence electrons of the atom − (the number of electrons in lone pairs + half the number of electrons in bonds with other atoms)). The sum of the formal charges on all the atoms in N2O is equal to zero. The most favored structure considers the minimization of the formal charges and the electronegativities of the atoms. Oxygen is more electronegative than nitrogen; therefore, the Lewis diagram that shows a negative formal charge on the oxygen atom is the best for depicting the molecule. Related Videos 2.6: Daily Video 1 2.6: Daily Video 2

In the following diagrams, elements are represented by X and Z, which form molecular compounds with one another. Which diagram represents a molecule that has a bent molecular geometry?

B) https://assets.learnosity.com/organisations/537/VH905963.g02.png Correct. There are four electron domains around the central atom X, and their geometry is tetrahedral, which minimizes the repulsion between the four electron pairs. The Z-X-Z bond angle is approximately 109.5°, and the molecular geometry is bent. Related Videos 2.7: Daily Video 1 2.7: Daily Video 2 2.7: Daily Video 3

Copper atoms and zinc atoms have the same atomic radius, 135 picometers. Based on this information, which of the following diagrams best represents an alloy containing only copper and zinc atoms?

B) https://assets.learnosity.com/organisations/537/VH906263.g02.png Correct. Being the same size, copper atoms and zinc atoms would form a substitutional alloy in which the atoms substitute for one another in a lattice of positive cores immersed in a sea of electrons. Related Videos 2.4: Daily Video 1

The energy required to dissociate an ionic solid into gaseous ions (lattice energy) for the compounds NaF and MgF2 is shown in the table above. On the basis of Coulomb's law, which of the following best helps to explain the large difference between the lattice energies of NaF and MgF2 ?

D) The charge of the Mg cation is larger than that of the Na cation. Correct. The coulombic attractions between the Mg cation and F anions are stronger because of the +2 charge on Mg as opposed to the +1 charge on Na. Stronger interionic attractions lead to a higher lattice energy.

Which of the following complete Lewis diagrams represents a molecule containing a bond angle that is closest to 120°?

D) https://assets.learnosity.com/organisations/537/VH903733.g04.png Correct. The carbon atom attached to the oxygen atoms exhibits sp2 hybridization, thus the bond angles around it are close to 120°. Another explanation is, the carbon atom attached to the two oxygen atoms is surrounded by three electron domains, which, according to VSEPR theory, will repel one another to produce a trigonal planar geometry around that atom. Related Videos 2.7: Daily Video 1 2.7: Daily Video 2 2.7: Daily Video 3