Unit 2 Learning Checkpoint 2

Which of the following is the complete Lewis diagram of NF3?

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A Lewis diagram of ammonia is shown. Which of the following claims about the polarity of the ammonia molecule is correct?

• The molecule is polar because there is a concentration of electrons near the nitrogen atom.
• The molecule is polar because it contains more hydrogen atoms than nitrogen atoms.
• The molecule is nonpolar because there is a lone pair of electrons on the nitrogen atom.
• The molecule is nonpolar because the electrons on the nitrogen atom are pulled toward the hydrogen atoms in the molecule.

Based on the molecular structures of chloromethane and methane shown, a student makes the claim that a pure sample of chloromethane has stronger intermolecular forces than a pure sample of methane has. Which of the following statements correctly uses reasoning to support the student’s claim?

• Chloromethane has a polar C–Cl bond, which allows for dipole-dipole interactions, but methane is nonpolar and only experiences dispersion forces.
• Chloromethane experiences stronger dipole-dipole interactions than methane does because the dipole of the C–Cl bond is canceled by the dipole from the C–H
• Chloromethane has stronger dispersion forces than methane has because of the nonpolar C–Cl bond in chloromethane.
• Chloromethane has stronger dispersion forces than methane has due to the highly polar C–H bonds in chloromethane

A student claims that the molecule represented in the diagram is nonpolar, so the substance has only London dispersion forces. Which of the following is the best evaluation of the student’s claim?

• The claim is correct; the dipoles cancel.
• The claim is correct; the atoms all lie on the same plane.
• The claim is incorrect; the geometry is tetrahedral and there are two different types of atoms around the C atom, so the dipoles do not cancel.
• The claim is incorrect; the atoms all lie on the same plane, so the dipoles cancel.

Some information about a compound is given in the table. A student claims that it is a covalent compound. Which property best supports the student’s claim?

• Electrical conductivity as a solid
• Boiling point
• Density as a liquid
• Color as a solid

A student performs tests on two compounds to help determine whether they have ionic or covalent bonding. The results are shown in the table. The results support which of the following statements about the compounds?

• Both compound X and compound Z are ionic.
• Both compound X and compound Z are covalent.
• Compound X is ionic, and compound Z is covalent.
• Compound X is covalent, and compound Z is ionic.

Scientists observe that the attractions between the ions in LiF are weaker than those in CaO. Diagrams of each ionic compound and information regarding the radius of each ion are shown. Based on the information, the best explanation for the weaker forces of attraction in LiF compared with those in CaO is that the lithium and fluoride ions in LiF ______

• are farther apart than the ions in CaO are
• are closer together than the ions in CaO are
• have a higher ionic charge than the ions in CaO have
• have a lower ionic charge than the ions in CaO have

Which of the following particle diagrams best represents the most common structure of solid sodium fluoride (NaF)?

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Which of the following particle diagrams best represents the compound sulfur dioxide (SO2)?

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A Lewis diagram for the amino acid glycine is shown. Four of the atoms are labeled w, x, y, and z. Which atom is in the center of a trigonal planar molecular geometry?

• N-w
• C-x
• C-y
• O-z