Van der Waals Forces Because of their structures, atoms of different elements do not all have the same ability to attract electrons. Some atoms have a stronger attraction for electrons than do other atoms. Therefore, when the atoms in a covalent bond share electrons, the sharing is not always equal. Even when the sharing is equal, the rapid movement of electrons can create regions on a molecule that have a tiny positive or negative charge.

When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. Chemists call such intermolecular forces of attraction van der Waals forces, after the scientist who discovered them. Although van der Waals forces are not as strong as ionic bonds or covalent bonds, they can hold molecules together, especially when the molecules are large.

ZOOMING IN

VAN DER WAALS FORCES AT WORK

A photograph shows the underside of a gecko lizard. The underside of the foot is zoomed to show it covered by minute hair like projections.

FIGURE 2–5 The underside of each foot on this Tokay gecko is covered by millions of tiny hairlike projections. The projections themselves are made of even finer fibers, creating more surface area for “sticking“ to surfaces at the molecular level. This allows geckos to scurry up walls and across ceilings.

2.1 Assessment

Review Key Concepts

    1. Review Describe the structure of an atom.

    2. Infer An atom of calcium contains 20 protons. How many electrons does it have?

    1. Review Why do all isotopes of an element have the same chemical properties?

    2. Compare and Contrast Compare the structure of carbon–12 and carbon–14.

    1. Review What is a compound?

    2. Apply Concepts Water (H2O) and hydrogen peroxide (H2O2) both consists of hydrogen and oxygen atoms. Explain why they have different chemical and physical properties.

    1. Review What are two types of bonds that hold the atoms within a compound together?

    2. Classify A potassium atom easily loses its one valence electron. What type of bond will it form with a chlorine atom?

Apply the Big idea

Matter and Energy

  1. Why do you think it is important that biologists have a good understanding of chemistry?

End ofPage 38

Table of Contents

Miller & Levine Biology
About the Authors
Changing the World of Biology Education
Contents
Diversity of Life: A Visual Guide DOL•1–DOL•64
Labs and Activities
Features
UNIT 1 The Nature of Life
1 The Science of Biology
2 The Chemistry of Life
Unit Project
UNIT 2 Ecology
3 The Biosphere
4 Ecosystems and Communities
5 Populations
6 Humans in the Biosphere
Unit Project
UNIT 3 Cells
7 Cell Structure and Function
8 Photosynthesis
9 Cellular Respiration and Fermentation
10 Cell Growth and Division
Unit Project
UNIT 4 Genetics
11 Introduction to Genetics
12 DNA
13 RNA and Protein Synthesis
14 Human Heredity
15 Genetic Engineering
Unit Project
UNIT 5 Evolution
16 Darwin's Theory of Evolution
17 Evolution of Populations
18 Classification
19 History of Life
Unit Project
UNIT 6 From Microorganisms to Plants
20 Viruses and Prokaryotes
21 Protists and Fungi
22 Introduction to Plants
23 Plant Structure and Function
24 Plant Reproduction and Response
Unit Project
UNIT 7 Animals
25 Introduction to Animals
26 Animal Evolution and Diversity
27 Animal Systems I
28 Animal Systems II
29 Animal Behavior
Unit Project
UNIT 8 The Human Body
30 Digestive and Excretory Systems
31 Nervous System
32 Skeletal, Muscular, and Integumentary Systems
33 Circulatory and Respiratory Systems
34 Endocrine and Reproductive Systems
35 Immune System and Disease
Unit Project
A Visual Guide to The Diversity of Life
HOW TO USE THIS GUIDE
THE TREE OF LIFE
Bacteria
Protists
Fungi
Plants
Animals
Appendices
Appendix A Science Skills
Appendix B Lab Skills
Appendix C Technology & Design
Appendix D Math Skills
Appendix E Periodic Table
Glossary
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q, R
S
T
U
V
W
X, Y, Z
Index
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Credits
Go to previous page Go to next page