Chemical Foundations of Life Practice Quiz (11 questions)

1. Which description best defines an atom?

A. The smallest unit of an element that has a different chemical identity

B. A substance that occupies space and contains several different elements

C. A particle made only of protons and neutrons in a central nucleus

D. The smallest unit of matter that retains an element’s chemical properties

Answer: (D)

Explanation

An atom is the smallest unit of matter that retains all the chemical properties of its element. A nucleus contains protons and neutrons, but it is not the full atom and does not include its surrounding electrons.

2. Which arrangement describes the basic structure of an atom?

A. Protons, neutrons, and electrons are distributed together throughout the atom

B. Protons and neutrons occupy the nucleus, while electrons are in the surrounding outer region

C. Electrons and protons occupy the nucleus, while neutrons are in the surrounding outer region

D. Neutrons and electrons occupy the nucleus, while protons are in the surrounding outer region

Answer: (B)

Explanation

An atom has a central nucleus containing protons and neutrons, with electrons in the surrounding outer region. The other arrangements incorrectly place one or more particle types in the nucleus or outer region.

3. What does the atomic number of an element represent?

A. The number of neutrons in the most common form of the element

B. The approximate total number of protons and neutrons in an atom

C. The number of protons in an atom of that element

D. The mass of an atom expressed in atomic mass units

Answer: (C)

Explanation

The atomic number is the number of protons, and each element has a distinct atomic number. The approximate combined mass of protons and neutrons describes atomic mass, not atomic number.

4. An atom has an atomic mass of 23 and an atomic number of 11; how many neutrons does it have?

A. 34 neutrons

B. 12 neutrons

C. 23 neutrons

D. 11 neutrons

Answer: (B)

Explanation

Subtracting the atomic number from the atomic mass gives the neutron count: $23 - 11 = 12$. The atomic number gives the proton count, so 11 is not the number of neutrons.

5. What does the Bohr model describe about the arrangement of electrons in an atom?

A. Electrons are embedded throughout a positively charged sphere.

B. Electrons remain inside the nucleus alongside protons and neutrons.

C. Electrons occupy probability distributions with no defined energy levels.

D. Electrons move in circular orbits at specific distances from the nucleus.

Answer: (D)

Explanation

The Bohr model places electrons in circular orbits at specific distances from the nucleus. The probability-distribution description refers instead to the quantum-mechanical account of orbitals.

6. How do reactants and products differ in a chemical reaction?

A. Reactants are substances that share electrons, while products transfer electrons.

B. Reactants are present at the start, while products are formed by the reaction.

C. Reactants are formed at the end, while products are present at the start.

D. Reactants are substances that reverse a reaction, while products prevent reversal.

Answer: (B)

Explanation

Reactants are the substances used at the beginning of a reaction, and products are the substances formed at its end. The electron-sharing distinction describes covalent bonding, not the roles of reactants and products.

7. What role do hydrogen bonds play between water molecules?

A. They create weak attractions between slightly positive hydrogens and slightly negative atoms on neighboring molecules.

B. They transfer electrons between neighboring molecules to create oppositely charged ions.

C. They share electrons equally between neighboring molecules to create nonpolar covalent bonds.

D. They link oxygen atoms into permanent covalent bonds that hold water molecules together.

Answer: (A)

Explanation

Water’s partial charges allow its slightly positive hydrogen atoms to attract slightly negative, more electronegative atoms on neighboring molecules, forming hydrogen bonds. Unlike ionic bonding, this attraction does not transfer electrons or create ions.

8. How do cohesion and adhesion differ in water’s interactions?

A. Cohesion is attraction between water and other materials, whereas adhesion is attraction among water molecules.

B. Cohesion is attraction among water molecules, whereas adhesion is attraction between water and other materials.

C. Cohesion describes heat absorbed during warming, whereas adhesion describes heat required for evaporation.

D. Cohesion describes water dissolving ions, whereas adhesion describes water changing into vapor.

Answer: (B)

Explanation

Cohesion arises from attraction among water molecules, while adhesion describes water’s attraction to different substances, such as glass. Water’s ability to dissolve ions is a solvent property, not the defining difference between these terms.

9. Why does ice float on liquid water?

A. Heating breaks hydrogen bonds and makes liquid water less dense than ice.

B. Adhesion between water molecules expands the liquid as it cools.

C. Hydrogen bonding forms an ice lattice that is less dense than liquid water.

D. Water’s high heat capacity prevents ice molecules from packing closely.

Answer: (C)

Explanation

As water freezes, hydrogen bonds create a crystalline lattice that is less dense than liquid water, so ice floats. The high heat capacity affects how much energy changes water’s temperature, not the density difference that makes ice float.

10. When designing a carbon-based molecular backbone that can branch into several directions, which structural feature of carbon makes this possible?

A. It has one outer-shell electron and can form three covalent bonds.

B. It has two outer-shell electrons and can form two covalent bonds.

C. It has four outer-shell electrons and can form four covalent bonds.

D. It has six outer-shell electrons and can form two covalent bonds.

Answer: (C)

Explanation

Carbon’s four outer-shell electrons allow it to form four covalent bonds, making it a versatile backbone for macromolecules. Having two outer-shell electrons would not provide the four bonding positions described for carbon.

11. What distinguishes an enantiomer from other types of isomers?

A. It differs in the arrangement of atoms around a carbon–carbon double bond.

B. It has a different chemical formula but a similar three-dimensional shape.

C. It has the same formula but a different covalent arrangement of its atoms.

D. It has the same formula and bonds but a three-dimensional arrangement that is a nonsuperimposable mirror image.

Answer: (D)

Explanation

Enantiomers share the same formula and covalent bonds but differ in three-dimensional arrangement as mirror images that cannot be superimposed. Structural isomers instead differ in how their atoms are covalently connected.