SECTION
2.1
ATOMS, IONS, AND MOLECULES
Study Guide
KEY CONCEPT
All living things are based on atoms and
their interactions.
MAIN IDEA:
VOCABULARY
atom
element
compound
ion
ionic bond
covalent bond
molecule
Living things consist of atoms of different elements.
1. How are atoms and elements related?
An element is a certain type of atom.
Copyright © McDougal Littell/Houghton Mifflin Company.
Sketch should resemble one of the illustrations in Figure 2.2 on page 37.
Nucleus should be in the center with protons and neutrons. Electrons should be
labeled in a ring surrounding the elements.
CHAPTER 2
Chemistry of Life
2. Sketch the structure of an atom. Label the protons, neutrons, nucleus, and electrons.
3. How do compounds differ from elements?
A compound is composed of atoms of different elements.
MAIN IDEA:
Ions form when atoms gain or lose electrons.
4. What is an ion?
an atom that has gained or lost one or more electrons.
5. Why does an ion have an electrical charge?
the number of protons no longer equals the number of electrons.
Unit 1 Resource Book
McDougal Littell Biology
Study Guide
31
STUDY GUIDE, CONTINUED
6. In the spaces provided below, sketch how both positive and negative ions form. Label
the nucleus and the electrons. Use Figure 2.3 as a reference.
CHAPTER 2
Chemistry of Life
Sketch should resemble the first
illustration in Figure 2.3, with one atom
losing an electron (becoming a positive
ion) and the other accepting that
electron (becoming a negative ion).
MAIN IDEA:
Atoms share pairs of electrons in covalent bonds.
7. What is a covalent bond?
A bond that forms between two atoms that share a pair of electrons.
8. What determines the number of covalent bonds that an atom can form?
Vocabulary Check
element
molecule
compound
ion
9. atoms held together by covalent bonds
compound
10. composed of different types of atoms
element
11. composed of one type of atom
ion
molecule
12. atom that has gained or lost electrons
13. What is the difference between how ionic and covalent bonds form?
Ionic bonds form between oppositely-charged ions; covalent bonds form when atoms
share a pair of electrons.
32
Study Guide
Unit 1 Resource Book
McDougal Littell Biology
Copyright © McDougal Littell/Houghton Mifflin Company.
the number of electron pairs that it needs to share to fill its outer energy level.