The Chemistry of Life ANSWER KEY

Section 2-1 The Nature of Matter (pages 35-39)
This section identifies the three particles that make up atoms. It also
explains how atoms of the same element can have a different number of
neutrons and describes the two main types of chemical bonds.

Atoms (page 35)
1. The basic unit of matter is called a(an) atom .

It is the center of an atom, made up of protons and
2. Describe the nucleus of an atom.

neutrons.

3. Complete the table about subatomic particles.

SUBATOMIC PARTICLES
Particle Charge Location in Atom
Proton – Positive – Nucleus
Neutron – Neutral – Nucleus
Electron – Negative- Surrounding nucleus
4. Why are atoms neutral despite having charged particles?
Atoms have equal numbers of electrons and protons, and these subatomic
particles have equal, but opposite, charges.

Elements and Isotopes (page 36)
5. What is a chemical element?
A chemical element is a pure substance that consists entirely of one type
of atom.

6. What does an element’s atomic number represent?
It represents the number of protons in an atom of the element.

7. Atoms of the same element that differ in the number of neutrons they
contain are known as isotopes.

8. How are isotopes identified? Isotopes are identified by their mass
number.

9. Why do all isotopes of an element have the same chemical properties?
They have the same chemical properties because they have the same number of
electrons.

Chemical Compounds (page 37)
10. What is a chemical compound?
A chemical compound is a substance formed by the chemical combination of
two or more elements in definite proportions.

11. What does the formula for table salt indicate about that compound? The
formula for table salt, NaCl, indicates that the elements from which table
salt forms-sodium and chlorine-combine in a 1:1 ratio.

Chemical Bonds (pages 38-39)
12. What holds atoms in compounds together? Chemical bonds
13. Complete the table about the main types of chemical bonds.

CHEMICAL BONDS
Type Formed when . . .

Covalent bond – Electrons are shared between atoms
Ionic bond – One or more electrons are transferred from one atom to another
14. What is an ion? An ion is an atom that is positively or negatively
charged because it has lost or gained electrons.

15. Is the following sentence true or false? An atom that loses electrons
has a negative charge.

– false
16. The structure that results when atoms are joined together by covalent
bonds is called a(an) molecule
17. Circle the letter of each sentence that is true about covalent bonds. =
A, B, D
18. The slight attraction that develops between oppositely charges regions
of nearby (polar) molecules are called Hydrogen bonds.

Section 2-2 Properties of Water (pages 40-43)
This section describes the makeup of water molecules. It also explains what
acidic solutions and basic solutions are.

The Water Molecule (pages 40-41)
1. Is the following sentence true or false? A water molecule is neutral.

true
2. What results from the oxygen atom being at one end of a water molecule
and the hydrogen atoms being at the other end?
The oxygen end of the molecule has a slight negative charge and the
hydrogen end has a slight positive charge.

3. Why is a water molecule polar?
There is an uneven distribution of electrons between the oxygen and
hydrogen atoms.

4. Circle the letter of each sentence that is true about hydrogen bonds. =
B, D (between Molecules!)
5. Complete the table about forms of attraction.

FORMS OF ATTRACTION
Form of Attraction Definition
CohesionAttraction between molecules of the same
substance
AdhesionAttraction between molecules of different
substances
6. Why is water extremely cohesive? It is very cohesive because of hydrogen
bonding.

7. The rise of water in a narrow tube against the force of gravity is
called capillary action
8. How does capillary action affect plants?
Capillary action is one of the forces that draws water out of the roots of
a plant and up into its stems and leaves.

Solutions and Suspensions (pages 41-42)
9. What is a mixture?
A mixture is a material composed of two or more elements or compounds that
are physically mixed together but not chemically combined.

10. A mixture of two or more substances in which the molecules of the
substances are evenly mixed is called a(an) Solution
11. The greatest solvent in the world is water
12. What is a suspension? A suspension is a mixture of water and
nondissolved substances that are so small they do not settle out.

13. Complete the table about substances in solutions.

SUBSTANCES IN SOLUTIONS
SubstanceDefinition
Saltwater Solution
Solute Substance that is dissolved
Table salt
SolventSubstance in which the solute dissolves
Water
Acids, Bases, and pH (pages 42-43)
14. Two water molecules can react to form