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Cover illustrations: © Tina Cash Walsh
Cover design: Paul McCarthy
FIRST EDITION
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:
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.
New terms appear in bold type and are defined in the Glossary.
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
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 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
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 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 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.
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.
Figure 1
Figure 2
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.
Can you use your periodic table to determine the element type of element #3, lithium (Li)?
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.
Figure 1
Figure 2
Booklets for the first 20 elements on the periodic table were made and used to learn the symbols and names of these elements.
Using your periodic table, can you organize the booklets in groups and periods?
Figure 3
Using your booklets, add the first 20 symbols to your periodic table.
An atom is composed of two regions:
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
Figure 2
Figure 3
Figure 4
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.
Compare the hydrogen isotopes in Figure 5. How are the isotopes alike? How are the isotopes different?
Figure 5
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
Figure 3
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.
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
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.
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:
Figure 3
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.
Can you identify the valence charge for the first 20 elements?
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
Identify the elements and number of atoms for the chemical formulas shown in the following table:
| Chemical Formula | Elements | Symbols | Number of Atoms |
| NaCl | |||
| C12H22O11 |
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:
Can you write the possible chemical formulas for the atomic structures in Figure 2?
Figure 2
(Structure A has 1 C and 1 O; structure B has 1 C and 2 O.)