Question 1

Which of the following best describes the representative unit of sodium chloride (NaCl)?

Accepted Answer

A formula unit representing the lowest whole-number ratio of Na⁺ and Cl⁻ ions

Question 2

Which compound would you expect to have the highest melting point based on its bonding and structure?

Accepted Answer

Silicon carbide ($$\mathrm{SiC})$$

Question 3

Which of the following statements about covalent network solids is correct?

Accepted Answer

They have very high melting points due to strong covalent bonds throughout the solid.

Question 4

Which of the following best explains why table salt ($$\mathrm{NaCl}) is a $$solid at room temperature?

Accepted Answer

It is held together by strong ionic bonds in a crystal lattice.

Question 5

Rank the following substances from lowest to highest boiling point: $$\mathrm{N_2O}$$, $$\mathrm{H_2O}$$, $$\mathrm{NaF}.$$

Accepted Answer

$$\mathrm{N_2O} \u003c \mathrm{H_2O} \u003c \mathrm{NaF}$$

Question 6

Which of the following compounds is a molecular (covalent) compound?

Accepted Answer

Water ($$\mathrm{H_2O})$$

Question 7

Which property is most characteristic of ionic compounds?

Accepted Answer

Conduct electricity when molten or dissolved in water

Question 8

Which of the following best describes an allotrope?

Accepted Answer

A different physical form of the same element with different atomic arrangements

Question 9

Which of the following compounds would you expect to be a gas at standard temperature and pressure (STP)?

Accepted Answer

Carbon dioxide ($$\mathrm{CO_2$})$$

Question 10

Which of the following best explains why water ($$\mathrm{H_2O}) $$has a higher boiling point than ammonia ($$\mathrm{NH_3$}) $$and hydrogen fluoride ($$\mathrm{HF}$$)?

Accepted Answer

Water forms the strongest hydrogen bonds among the three.

Question 11

Which of the following is NOT a property of covalent network solids?

Accepted Answer

Usually soft and volatile

Question 12

A student observes that dry ice (solid $$\mathrm{CO_2$}) $$sublimes at room temperature. Which property of $$\mathrm{CO_2$}$$ explains this behavior?

Accepted Answer

Weak dispersion forces between molecules

Question 13

Which of the following best describes the bonding in graphite?

Accepted Answer

Each carbon atom is bonded to three others in flat layers with delocalized electrons

Question 14

Which of the following compounds would conduct electricity when dissolved in water?

Accepted Answer

Sodium chloride ($$\mathrm{NaCl})$$

Question 15

Which of the following best explains why diamond is one of the hardest substances known?

Accepted Answer

It is a covalent network solid with each carbon atom bonded to four others in a 3D network.

Question 16

Which of the following is the correct order of melting points from highest to lowest for the following types of substances?

Accepted Answer

Covalent network solids \u003e Ionic compounds \u003e Molecular compounds with hydrogen bonds \u003e Molecular compounds with dispersion forces

Question 17

Which of the following is a correct example of an allotrope of carbon?

Accepted Answer

Diamond and graphite

Question 18

Which of the following best describes the main intermolecular force in ammonia ($$\mathrm{NH_3$}$$)?

Accepted Answer

Hydrogen bonding

Question 19

A compound is composed of a metal and a nonmetal. Which type of compound is it most likely to be?

Accepted Answer

Ionic compound

Question 20

Which of the following substances is most likely to be volatile at room temperature?

Accepted Answer

Carbon dioxide ($$\mathrm{CO_2$})$$

Physical Properties of Materials: Ionic, Molecular, and Covalent Network Compounds

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