Janice VanCleave's Big Book of Science Experiments E-Book

Janice VanCleave

• Herausgeber: John Wiley & Sons
• Kategorie: Bildung
• Sprache: Englisch

Seitenzahl: 370

Veröffentlichungsjahr: 2020

Beschreibung

Janice VanCleave once again ignites children's love for science in her all-new book of fun experiments--featuring a fresh format, new experiments, and updated content standards From everyone's favorite science teacher comes Janice VanCleave's Big Book of Science Experiments. This user-friendly book gets kids excited about science with lively experiments designed to spark imaginations and encourage science learning. Using a few handy supplies, you will have your students exploring the wonders of science in no time. Simple step-by-step instructions and color illustrations help you easily demonstrate the fundamental concepts of astronomy, biology, chemistry, and more. Children will delight in making their own slime and creating safe explosions as they learn important science skills and processes. Author Janice VanCleave passionately believes that all children can learn science. She has helped millions of students experience the magic and mystery of science with her time-tested, thoughtfully-designed experiments. This book offers both new and classic activities that cover the four dimensions of science--physical science, astronomy, Biology, and Earth Science--and provide a strong foundation in science education for students to build upon. An ideal resource for both classroom and homeschool environments, this engaging book: * Enables students to experience science firsthand and discuss their observations * Offers low-prep experiments that require simple, easily-obtained supplies * Presents a modern, full-color design that appeals to students * Includes new experiments, activities, and lessons * Correlates to National Science Standards Janice VanCleave's Big Book of Science Experiments is a must-have book for the real-world classroom, as well as for any parent seeking to teach science to their children.

Leseprobe

Table of Contents

Cover

Introduction

The Activities

General Instructions

Measurements

Part I: CHEMISTRY

Matter

01 The Periodic Table

02 Element Symbols

03 Atomic Structure

04 Lewis Dot Diagrams

05 Ions

06 Chemical Formulas

07 Ionic Compounds

08 Covalent Compounds

09 Atoms vs. Molecules

10 Heterogeneous Mixtures

11 Solution: Concentration

12 Solubility

13 True Solutions

14 Colloids

15 Emulsions

16 Suspensions

17 Saturated Solutions

18 Diffusion

Physical Properties and Physical Changes

19 Matter Has Mass

20 Matter Has Volume

21 Relative Density

22 States of Matter

Chemical Properties and Chemical Changes

23 Acids

24 Bases

25 pH Scale

26 Combination and Decomposition Reactions

27 Leavening Agent

28 Balancing Chemical Equations

29 Combustion: Burning

30 Exothermic Chemical Reactions

31 Explosions

32 Polymers: Slime

Part II: PHYSICS

Newton's Laws of Motion

33 Newton's First Law of Motion: Inertia

34 Newton's Second Law of Motion

35 Newton's Third Law of Motion

Forces

36 Freefall

37 Gravity

38 Momentum

39 Apparent Weightlessness

40 Buoyancy

41 Buoyant Force

42 Friction

43 Torque

44 Center of Gravity

45 Stability

Heat

46 Conduction of Heat

47 Convection

48 Conductors vs. Insulators

49 Heat Capacity

Light

50 Electromagnetic Spectrum

51 Photons

52 Phosphors

53 Fluorescence

54 Phosphorescence

55 Colors You See

56 Convex Lenses: Focal Length

57 Convex Lenses: Rules of Refraction

58 Convex vs. Concave Lenses

Electricity

59 Series Circuit

60 Parallel Circuit

61 Energy Ball

Part III: ASTRONOMY

Space Measurements

62 Models of the Universe

63 Space Measurements

64 Apparent Sizes of Celestial Objects

65 Angular Distances

66 Sun Shadows

67 Albedo

The Moon

68 Moon Phases

69 The Terminator

70 Barycenter

71 Moon Motion

Constellations

72 Circumpolar Constellations

73 Location of Polaris

74 Zodiac Constellations

Part IV: EARTH SCIENCE

Geology

75 Density of Earth’s Layers

76 Volcanoes

77 Evaporites

78 Fossils

79 Tectonic Plates

80 Deformation

81 Fold Mountains

82 Tension

83 Normal and Reverse Faults

Meteorology

84 Climate

85 Atmospheric Pressure

86 Sea and Land Breezes

87 Rayleigh Scattering

88 Seasons

89 Coriolis Effect

Part V: BIOLOGY

The Nervous System

90 Eukaryotic Cells

91 Muscles

92 Afterimage

93 Perception of Color

94 Reaction Time

95 Sensory Receptors

Physical and Biochemical Changes

96 Chromatography

97 Denaturing Egg Protein

98 Denaturing Milk Protein

99 Ripening Hormone

100 Bioluminescence

Glossary

Index

End User License Agreement

List of Illustrations

Matter

Figure 1

Chapter 1

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Figure 2

Chapter 2

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Figure 3

Chapter 3

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Figure 2

Figure 3

Figure 4

Figure 5

Chapter 4

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Chapter 5

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Chapter 6

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Chapter 7

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Chapter 8

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Chapter 9

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Chapter 10

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Chapter 11

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Chapter 12

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Chapter 13

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Chapter 14

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Chapter 15

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Chapter 16

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Chapter 17

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Chapter 18

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Chapter 19

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Chapter 20

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Chapter 21

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Chapter 22

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Chapter 23

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Chapter 24

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Chapter 25

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Chapter 26

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Chapter 27

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Chapter 28

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Chapter 29

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Chapter 30

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Chapter 31

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Chapter 32

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Chapter 33

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Chapter 34

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Chapter 35

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Chapter 36

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Chapter 37

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Chapter 38

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Chapter 39

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Chapter 40

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Chapter 41

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Chapter 42

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Chapter 43

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Chapter 44

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Chapter 45

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Chapter 46

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Chapter 47

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Chapter 48

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Chapter 49

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Chapter 50

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Chapter 51

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Chapter 52

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Chapter 53

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Chapter 54

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Chapter 55

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Chapter 56

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Chapter 57

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Chapter 58

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Chapter 59

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Chapter 60

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Chapter 61

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Chapter 62

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Chapter 63

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Chapter 64

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Chapter 65

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Chapter 66

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Chapter 67

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Chapter 68

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Chapter 69

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Chapter 70

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Chapter 71

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Constellations

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Chapter 72

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Chapter 73

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Chapter 74

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Chapter 75

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Chapter 76

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Chapter 77

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Chapter 78

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Chapter 79

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Chapter 80

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Chapter 81

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Chapter 82

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Chapter 83

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Chapter 84

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Chapter 85

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Chapter 86

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Chapter 87

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Chapter 88

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Figure 6

Chapter 89

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Chapter 90

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Chapter 91

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Chapter 92

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Chapter 93

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Chapter 94

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Chapter 95

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Chapter 96

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Figure 7

Chapter 97

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Chapter 98

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Chapter 99

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Chapter 100

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Figure 6

Guide

Cover

Table of Contents

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Janice VanCleave’sBIG BOOKOF SCIENCE EXPERIMENTS

Janice VanCleave

Copyright © 2020 by John Wiley & Sons, Inc. All rights reserved.

Published by Jossey‐BassA Wiley Brand111 River Street, Hoboken NJ 07030www.josseybass.com

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the publisher, or authorization through payment of the appropriate per‐copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, 978‐750‐8400, fax 978‐646‐8600, or on the Web at www.copyright.com. Requests to the publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, 201‐748‐6011, fax 201‐748‐6008, or online at www.wiley.com/go/permissions.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Readers should be aware that Internet Web sites offered as citations and/or sources for further information may have changed or disappeared between the time this was written and when it is read.

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Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some material included with standard print versions of this book may not be included in e‐books or in print‐on‐demand. For more information about Wiley products, visit www.wiley.com.

Library of Congress Cataloging‐in‐Publication Data is available for this title

Cover illustrations: © Tina Cash WalshCover design: Paul McCarthyFIRST EDITION

Introduction

Throughout the writing of this book, I imagined the reader delving into the exciting world of science exploration. It was and is my fervent hope that this science book will ignite a profound curiosity for scientific discovery in children of all ages! As this leads to a deeper understanding about the world around us, I believe that the future holds a rich promise for scientific challenges to be solved by these young scientists.

The order of presentation is designed to give you a platform to build on, starting with the basic foundation of all sciences, matter – the stuff the Universe is made up of. The activities in a specific topic do build in content, and you are encouraged to work through them in order. But although it is best to work your way through the book, most activities do stand on their own. (Some investigations require materials built in previous activities.) With the help of the glossary as well as introductions for the different topics, you can pick and choose any investigation and be rewarded with a successful experiment. Of course, your success depends on your attentiveness to following the procedure steps in order. Substituting equipment can affect the results for some activities, but for the most part just use your common sense about changes.

This book is designed to give the reader a taste of different sciences:

Chemistry

 The study of the composition of matter and how it interacts, combines, and changes to form new substances.

Physics

 The study of energy and forces and their interaction with matter.

Astronomy

 The study of the Universe and Earth's position in it; the study of Earth's visible neighbors in space.

Earth Science

 The study of the unique habitat that all known living creatures share – the Earth.

Biology

 The study of the body systems of living organisms; the study of physical and biochemical changes.

The Activities

The activities follow a set step‐by‐step pattern, and generally start with a science problem to solve or purpose to investigate. The goal of this book is to guide you through the steps necessary in successfully completing a science experiment and to present methods of solving problems and discovering answers. It also provides a thought‐provoking question about each experiment with steps for thinking through the information in order to arrive at a solution.

Introduction:

Background information provides knowledge about the topic of the investigation.

See for Yourself:

A list of necessary materials and step‐by‐step instructions on how to perform the experiment.

What Happened?

A statement of what should happen; an explanation of why the results were achieved in terms that are understandable to readers who may not be familiar with the scientific terms introduced.

Challenge:

A question related to the investigation, with step‐by‐step clues for thinking through the answer.

New terms appear in bold type and are defined in the Glossary.

General Instructions

Read first.

 Read each experiment completely before starting.

Collect needed supplies.

 You will experience less frustration and more fun if all the necessary materials for the experiments are ready for instant use. You lose your train of thought when you have to stop and search for supplies.

Experiment.

 Follow each step very carefully, never skip steps, and do not add your own. Safety is of the utmost importance, and by reading the experiment before starting, then following instructions exactly, you can feel confident that no unexpected results will occur.

Observe.

 If your results are not the same as described in the experiment, carefully read the instructions and start over from the first step. Consider factors such as the temperature, humidity, lighting, and so on that might affect the results.

Measurements

Measuring quantities described in this book are given in the English imperial system followed by approximate metric equivalents in parentheses. Unless specifically noted, the quantities listed are not critical, and a variation of a very small amount more or less will not alter the results.

I hope you have fun as you learn about the beautiful world we live in!

—Janice VanCleave

Part ICHEMISTRY

Chemistry is the study of matter, its physical and chemical properties, and how it changes. This science involves all of one's senses: seeing, hearing, tasting, feeling, and smelling. It is listed first in this book because chemistry concepts are a springboard into the other sciences. You cannot understand the physics concept of electricity without understanding the chemistry of atoms, or the formation of crystals in caves in earth science, or biochemical reactions in the fruit ripening process in biology without understanding chemical reactions.

Chemistry is not restricted to scientists working in laboratories; instead, knowledge of chemistry is important in our everyday lives. Who knows? You might be on some reality show or confronted with an unexpected survival situation. You would be cut off from electrical devices. Chemistry knowledge would help you use available resources. Yes, your brain is your best survival tool in emergencies; but it is also the best problem‐solving tool you have. Chemistry is all about problem solving, and the investigations in this book contain the foundation on which to build and sharpen your chemistry knowledge.

Matter

Matter is anything that occupies space and has mass (an amount of matter making up a material). Matter is the stuff that makes up the Universe. Figure 1 shows a flow chart for the different types of matter. The term pure substance refers to one kind of matter, such as an element or a compound; without the adjective “pure,” the term substance is commonly used to refer to any material pure or not, and that is how it is used in this book. Mixture is a term that refers to the combination of different substances.

Figure 1

Elements

At this time, 118 different elements have been identified. The 94 elements that occur in nature are called natural elements, examples being carbon, oxygen, nitrogen, and sulfur. Synthetic elements are the 24 elements made by scientists in a laboratory. Synthetic elements include californium, plutonium, nobelium, and einsteinium.

The periodic table is a chart that lists all the known elements. The placement of elements on this table gives clues as to their physical structure, their physical characteristics, and how they might react with other elements. Understanding the periodic table is like having a special condensed code book.

Compounds

Compounds are substances made of two or more different elements combined in a certain ratio with the elements bonded (linked) together. There are two types of compounds, covalent and ionic. The difference between the two is in how they are bonded together. Covalent compounds have covalent bonds that form between two atoms that share electrons. Molecules are the smallest building blocks for covalent compounds that can exist independently. Ionic compounds have positive and negative ions as their building blocks.

Mixtures

Mixtures are the combination of two or more substances, where each substance retains its own chemical properties. There are two basic types of mixtures, homogeneous and heterogeneous. Homogeneous mixtures are the same throughout; they have the same uniform appearance as well as composition throughout. Heterogeneous mixtures are not the same throughout. This type of mixture has visibly different substances, such as a mixture of ice and soda or a mixture of fruit in a bowl.

01The Periodic Table

The periodic table of elements contains 118 elements, of which 94 are natural and the remaining 24 are synthetic. Each element is given a specific number called the atomic number, used to place elements in a specific location on the table.

The rows on the periodic table are called periods and are numbered from 1 through 7; elements are arranged from left to right across each row by increasing atomic number. The columns on the table are called groups or families and are numbered from 1 through 18. The periodic table can be color‐coded to identify the location of the major types of elements; each type falls in a region that overlaps different periods and groups. Metals are typically solids that are hard, but are easy to bend or stretch into a wire. Nonmetals typically are dull solids with characteristics opposite to those of metals.

See for Yourself

Materials

sheet of graph paper

ruler

pen

colored pens

What to Do

Use

Figure 1

to create your own periodic table by drawing the boxes on graph paper, then number the periods and groups as shown. Keep and use your periodic table for other activities.

Figure 1

Use the numbers in

Figure 2

as clues to help you number all 118 boxes on your periodic table. Remember, the numbers increase from left to right across each row.

Figure 2

This time, use

Figure 2

as a guide to color‐code these nine different sections on your periodic table. The colors you choose aren't significant; one possible set may be:

purple (group 1):

alkaline metals; very reactive metals.

blue (group 2):

alkaline earth metals; more reactive than other metals, but less than alkaline metals.

lime green (groups 3–12):

transition metals; have a different atomic structure from other metals.

yellow:

basic metals.

red:

metalloids; have metallic and nonmetallic characteristics.

dark green:

basic nonmetals; group 17 comprises the halogen gases, which are the most reactive nonmetals.

pink (group 18):

noble gases; react under special conditions.

light blue (period 6 elements 57–70):

lanthanide series; separated from the table because of the difference in their physical atomic structure.

orange (period 7 elements 89–102):

actinide series; separated from the table because of the difference in their physical atomic structure.

Add a legend to your periodic table that represents the color‐coding used.

What Happened

The different types of elements on the periodic table have been identified. There are more metals than any other type of element on the table. The nonmetals are listed on the right side of the periodic table. The red zig‐zag line in Figure 2 contains metalloids, which have both metallic and nonmetallic properties. The metalloids basically separate the metals from the nonmetals.

Challenge

Can you use your periodic table to determine the element type of element #3, lithium (Li)?

Think!

Element #3 is found in group 1 on the periodic table.

Using the legend for your periodic table, identify the type of elements found in group 1.

With the exception of element #1, hydrogen (H), which is a gas, all elements in group 1 of the periodic table are solid alkaline metals.

Lithium (Li) is an alkaline metal.

02Element Symbols

Elements, the building blocks of matter, are pure substances made up of atoms. A chemical symbol is much like a code that represents the name of an element. A chemical symbol has one or two letters. A capital letter is used for symbols with one letter — for example, H for hydrogen and C for carbon. Symbols with two letters start with a capital letter and the second letter is lowercase — for example, He for helium.

(Some older periodic tables have a few three‐letter symbols, such as Uup for ununpentium. This means “115,” which is the atomic number of this manmade element. As of 2016, all 118 elements have names and one‐ or two‐letter symbols. Element 115 is called moscovium, Mc.)

The symbol and name do not always match, such as Na for sodium and Au for gold. (Na is from the Latin word natrium and Au is from the Latin word aurium.) Few people memorize all 118 known elements, but someone studying science should become familiar with the first 20 elements shown in the table. Element booklets can be used to become more familiar with individual elements and their symbols as well as their location on the periodic table.

See for Yourself

Materials

20 sheets of blank paper

black marker

your periodic table from experiment #1, “The Periodic Table”

What to Do

Make a booklet by folding one of the sheets of paper in half twice, first from top to bottom, and then from side to side (

Figure 1

).

Figure 1

Prepare a booklet for aluminum, Al, the first element in the alphabetical list of elements by symbol in the table. Use the marker to print the symbol for aluminum and its atomic number on the front of the booklet and the name on the back as shown in

Figure 2

.

Figure 2

Repeat steps 1 and 2 making booklets for the remaining 19 elements in Table 1.

Stack the 20 booklets with symbols face up. One at a time, looking at the symbol of the first booklet in the stack, identify the name of the element.

Turn the top booklet over. If you correctly identified the name of the element lay it name side up on the table. If your answer was wrong, start a second stack of booklets with symbol side up.

Repeat step 5 until you have gone through all 20 booklets.

Start over using the new stack of booklets. Continue until you can correctly match the symbol and name of all 20 elements.

Now repeat step 5 giving the symbol for each name.

Keep the booklets and add information as you learn more about the elements.

What Happened

Booklets for the first 20 elements on the periodic table were made and used to learn the symbols and names of these elements.

Challenge

Using your periodic table, can you organize the booklets in groups and periods?

Think!

Periods are horizontal rows.

Groups are vertical columns.

Figure 3

shows the atomic numbers of the first 20 elements of the periodic table.

Figure 3

Using your booklets, add the first 20 symbols to your periodic table.

03Atomic Structure

An atom is composed of two regions:

the center of the atom, called the nucleus, which contains protons (P1+) and neutrons (n0);outside the nucleus, at fixed distances, are energy levels or orbitals with electrons (e1−) having different amounts of energy.

The period number on the periodic table equals the number of energy levels for every element in that period. An element's mass number is the sum of the protons and neutrons in the nucleus of that element's atoms. An element's atomic number is equal to the number of protons in the nucleus and is equal to the number of electrons outside the nucleus in energy levels.

Figure 1 shows the atomic number, mass number and group A numbers for the first 20 elements. Add these to your own periodic table so that it can be used to draw atomic structures.

Figure 1

See for Yourself

Materials

black marker

element booklets (from experiment #2)

periodic table (from experiment #1)

Figure 2

What to Do

For each element booklet, add the mass number to the symbol of each element. The symbol for calcium should look like this:

20

Ca

40

.

Use the atomic number of 20 and mass number of 40 to determine the number of neutrons in a calcium atom.

Inside the booklet for calcium, draw a circle and add the protons and neutrons found there.

Use the following to add the energy levels outside the nucleus:

Find the element in the periodic table: The period number of the element equals the number of energy levels.

Use curved lines to represent the energy levels, as shown in

Figure 3

.

Figure 3

Use the following to add electrons to each energy level:

The number of electrons in an atom is equal to the number of protons (atomic number).

For calcium there are 20 electrons: The first level has 2e

−

, second level has 8e

−

, third level has 8e

−

, and the fourth level has the remaining 2e

−

.

Figure 4

Repeat the previous procedure to draw atomic structures inside the remaining 19 element booklets.

What Happened

The atomic structures for elements #1 through #20 were drawn in element booklets. Although the atomic number of an element does not change, its mass number can. This is due to differences in the number of neutrons in the atoms of an element. Atoms of the same element with different numbers of neutrons are called isotopes. Magnesium has 18 isotopes, of which Mg‐24 is the most common. Mg‐24 represents a magnesium atom with a mass number of 24.

Challenge

Compare the hydrogen isotopes in Figure 5. How are the isotopes alike? How are the isotopes different?

Think!

Each isotope of hydrogen has the same atomic number of one. This is because all atoms of hydrogen have the same number of protons, which is one.

The isotopes all have the same number of energy levels and the same number of electrons. This is because the isotopes are all hydrogen atoms, which have the same number of electrons and protons.

The isotopes all have a different mass number because, as isotopes, they all have a different number of neutrons.

Figure 5

04Lewis Dot Diagrams

A Lewis dot diagram is a representation of an element's valence electrons, which are the electrons in an atom's outermost energy level. Lewis dot diagrams are composed of an element's symbol with dots representing electrons placed around the symbol. Lewis dot diagrams represent neutral atoms, which means the number of protons in the nucleus is equal to the total number of electrons outside the nucleus.

In reality, there is no set placement of electrons because they are in constant motion. If the position of an electron at any one time were marked, the pattern of electron movement would look much like the electron cloud illustration in Figure 1. Note the density of the cloud is greatest near the nucleus and least at its edges. This is because the attraction between the negatively charged electrons and the positively charged nucleus is greater the closer the electrons are to the nucleus.

Figure 1

The Lewis dot diagram is used to show the number of valence electrons. The dot diagram for neon (Ne) in Figure 2 can be used as a guide for placing valence electrons. Make note that, for known elements, there are never more than eight valence electrons. Neon is in group 8A and has the maximum number of valence electrons. The number of valence electrons for group A elements is equal to the group A number. With the pattern for placing the electrons in Figure 2, dot diagrams for all group A elements are easy to draw.

Figure 2

See for Yourself

Materials

element booklets (from experiment #2)

black marker

periodic table (from experiment #1)

What to Do

Open the nitrogen element booklet and on the left side write the symbol for nitrogen below the atomic structure for nitrogen.

Use the following instructions to draw a dot diagram for nitrogen (N).

Locate nitrogen on the periodic table. The group A number of nitrogen is equal to its number of valence electrons.

Now, using the placement order of electrons shown in

Figure 3

for nitrogen, make dots around the symbol, N.

Repeat the procedure drawing dot diagrams for each element inside their element booklet.

Figure 3

What Happened

Nitrogen is in group 5A. Thus, all the elements in this vertical group have five valence electrons. Using Group A numbers, dot diagrams for each element #1 through #20 were drawn in their element booklets.

Ions are atoms that have either lost or gained electrons. Metals tend to lose their valence electrons, forming positive ions called cations; nonmetals tend to gain electrons, forming negative ions called anions.

Challenge

The Lewis dot diagrams can be used to show how cations and anions are formed. Can you explain how the ions in Figure 4 are formed?

Figure 4

Think!

Nitrogen gains electrons and sodium loses electrons.

Neutral atoms have the same amount of positive and negative charges; the same number of protons as electrons.

Electrons have a negative charge; when electrons are gained by an atom it has more negative electrons than positive protons.

Nitrogen gains three electrons, thus an anion with a 3− charge is formed.

When an atom loses electrons, it becomes positively charged because it has more protons than electrons; sodium forms a cation with a 1+ charge.

Did you notice that anions have a suffix of ‐ide, while cations maintain the name of the element? You will use this information in the next activity.

The electrons farthest from the nucleus are more likely to be involved in chemical reactions; these are the valence electrons.

05Ions

Ions are atoms that have either gained or lost valence electrons, thus forming charged particles. For this activity, the formation of ions will be limited to elements #1 through #20 on the periodic table. Atoms that lose electrons form positive ions called cations. In Figure 1, the dot diagram for the element sodium is used to show the loss of its valence electron, thus forming a cation and one free electron. Note the atomic structure of sodium in Figure 1; when its valence electron is lost there are 10 remaining electrons and the nucleus still has 11 protons. The atom now has a positive charge because it has more protons than electrons.

Figure 1

Electronegativity is a measure of how strongly electrons are attracted to the nucleus of an atom. The element with the lowest electronegativity is to the left in a period and at the bottom of a group.

Atoms that gain electrons form negative ions called anions. In Figure 2, the dot diagram for the element chlorine is used to show the formation of an anion. Chlorine atoms have an equal number of protons and electrons and seven valence electrons. The formation of a chloride ion occurs when a chlorine atom gains one electron to fill the outer energy level and forms an anion with a charge of negative 1. Note that the charge on an ion is written as a superscript above and to the right of the element's symbol. Charges on ions, whether positive or negative, are called valence charges.

Figure 2

A general rule that can be used to determine whether an atom loses or gains electrons when reacting with another element is:

Elements with 1, 2, or 3 valence electrons lose all valence electrons, forming cations.Elements with 5, 6, or 7 valence electrons gain electrons so that there are 8 valence electrons, forming anions.Elements with 4 valence electrons can gain electrons if they react with an element with a lower electronegativity, or lose 4 electrons if they react with an element with a higher electronegativity.The inert gases in group 8A do not generally form ions.

See for Yourself

Materials

element booklets (from experiment #2)

black marker

What to Do

Start with the hydrogen booklet. Open the booklet and use the Lewis dot diagram to write an equation to show how hydrogen atoms form ions.

Use chlorine in

Figure 2

as an example.

Write the symbol for hydrogen with its valence charge as a superscript.

Elements in groups 1A, 2A, and 3A tend to lose all their valence electrons, forming cations.

Elements in group 4A can lose or gain 4 electrons depending on what they react with. Write two equations for elements in this group.

Elements in groups 5A–7A gain up to 8 valance electrons, forming anions.

Elements in group 8A do not generally form ions. No equation is needed.

Repeat step 1, writing equations to show how each of the remaining 19 elements form ions, omitting group 8A.

Close the booklets and on the back of each booklet write the symbol and its valence charge in the upper left corner.

Figure 3

What Happened

The equation for ion formation of the first 20 elements on the periodic table was written in individual element booklets. The symbol and its valence charge were written on the back of each of the booklets.

Challenge

Can you identify the valence charge for the first 20 elements?

Think!

One way to memorize the valence charges of elements is by using the element booklets.

Stack the booklets with the symbol side up.

Look at the symbol on the top booklet; identify the name of the symbol; and then identify the valence charge for the element.

Turn the booklet over and check your answers.

Repeat until you can identify the valence charge of all the first 20 elements. Note: Inert gases have no charge.

06Chemical Formulas

A compound contains two or more different elements; for example, water is a compound containing two elements, hydrogen and oxygen. The chemical formula for water is H2O. Every chemical formula is a combination of elemental symbols showing the elements as well as the number of atoms of each element.

Figure 1

See for Yourself

Materials

paper and pencil

What to Do

Identify the elements and number of atoms for the chemical formulas shown in the following table:

Chemical Formula

Elements

Symbols

Number of Atoms

NaCl

C

12

H

22

O

11

What Happened

Alphabet letters are used to write words, but elemental symbols are used to write chemical formulas for compounds. A word is composed of letters in a specific order; a chemical formula is composed of elemental symbols in a specific order. When writing words, such as “see,” letters are repeated, but this is not true in chemical formulas.

Washing soda (Na2CO3) has three symbols: Na, C, and O. Subscripts for Na and O indicate the number of atoms of these elements. Thus, instead of writing the formula for baking soda as NaNaCOOO, subscripts follow a symbol to indicate the number of atoms. A symbol without a number indicates one atom, so no subscript is needed for C.

The kind and number of atoms in the chemical formula for table salt, NaCl, and for table sugar, C12H22O11, are shown here:

Challenge

Can you write the possible chemical formulas for the atomic structures in Figure 2?

Figure 2

Think!

What are the kind and number of atoms in each of the two atomic structures?

(Structure A has 1 C and 1 O; structure B has 1 C and 2 O.)

Carbon and oxygen are both in period 2 of the periodic table; oxygen is further to the right; thus, oxygen has the greater electronegativity (affinity for electrons) and will be the negative partner in the formula.

When writing a formula, always write the positive element first and the negative element second.

Structure A is carbon monoxide and its correct formula is CO; structure B is carbon dioxide and its formula is CO

2

.

It is important to write chemical formulas correctly. Slight differences matter. For example, the formulas CO and CO

2