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1 Standards Preview Physical Sciences Standard Set 1. Physical Sciences 1. Elements and their combinations account for all the varied types of matter in the world. As a basis for understanding this concept: 1.b. Students know all matter is made of atoms, which may combine to form molecules. 1.c. Students know metals have properties in common, such as high electrical and thermal conductivity. Some metals, such as aluminum (Al), iron (Fe), nickel (Ni), copper (Cu), silver (Ag), and gold (Au), are pure elements; others, such as steel and brass, are composed of a combination of elemental metals. 1.d. Students know that each element is made of one kind of atom and that the elements are organized in the periodic table by their chemical properties. 1.e. Students know scientists have developed instruments that can create discrete images of atoms and molecules that show that the atoms and molecules often occur in wellordered arrays. 1.f. Students know differences in chemical and physical properties of substances are used to separate mixtures and identify compounds. 1.h. Students know living organisms and most materials are composed of just a few elements. 1.i. Students know the common properties of salts, such as sodium chloride (NaCl). by Johanna Biviano Genre Comprehension Skill Text Features Science Content Nonfiction Make Inferences Captions Diagrams Labels Glossary Matter Scott Foresman Science 5.1 ì<(sk$m)=cdfged< +^-Ä-U-Ä-U ISBN

2 Vocabulary atom atomic number chemical property compound element molecule physical property solution by Johanna Biviano Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Unless otherwise acknowledged, all photographs are the copyright of DK Images, a division of Pearson. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). 1 DK Images; 7 CDC/PHIL/Corbis; 10 (R) DK Images; 12 DK Images; 13 (L) Philip Dowell/DK Images, (R) Getty Images; 14 (B) Spencer Jones/Getty Images; 17 DK Images; 19 DK Images; 20 DK Images; 22 DK Images. ISBN: Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois V

3 Properties of Matter In the mid-1800s, the Gold Rush brought people from all over the world to California. Miners were looking for nuggets of gold like the one below. The gold they were hoping to find is a basic kind of matter called an element. Elements are the building blocks of matter. They cannot be broken down into smaller pieces. Out of more than 100 elements, only a few exist in nature in a pure form. Gold is one of them. In fact, most matter is made up of groups of elements. Almost all of Earth s crust is made up of eight elements. They are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Most living and nonliving things are made up of a few elements that combine in several ways. Gold is an element. This balance is one tool that can measure physical properties. Elements have distinct properties from one another. They have physical properties that can be seen or measured without changing the material. A physical property is often obvious to one of your five senses. Color, odor, and hardness are physical properties. There are different tools you can use to measure physical properties. These include metersticks, balances, and spring scales. Electron microscopes help scientists look at the structure of elements. An element s chemical properties have more to do with how an element reacts with other elements. 2 3

4 Physical Properties You can tell a lot about an element s physical properties by looking at it and touching it. From the picture of silver, you can see that it is gray and shiny. If you could touch it, it would feel solid. The color and phase of matter (solid, liquid, gas) are physical properties. Silver also has mass and weight. You can measure silver to find its mass. Finding the mass with a balance will tell you how much matter is in an object. The weight of silver can be determined with a spring scale. This piece of silver will always have the same mass, but its weight can change. Weight is a measure of how much gravity affects an object. Let s say this silver weighs six pounds at sea level. On the Moon, where there is less gravity, it would only weigh one pound! Magnetism, the temperatures at which a substance boils and freezes, and a substance s ability to dissolve are all physical properties. Oxygen and water cause iron to rust. Silver is a pure element. Chemical Properties Using chemical properties is a useful way to identify substances. Chemical properties can be seen when you combine one substance with another. Remember that iron turns to rust when it is combined with water and oxygen. This is a chemical property of iron. Iron is easy to bend and shape. This is a physical property called malleability. Bending iron doesn t create a chemical reaction, but adding oxygen and water does. Another chemical property is flammability. This is the ability of a substance to burn. 4 5

5 Parts of Matter An atom is the smallest particle of an element that has the same properties of the element. The atoms in one element are different from the atoms in another element. The structure of atoms determines the chemical and physical properties of an element. It also shows how an element can combine with other elements. Pure metals, such as silver, are made up of only one kind of atom. This means they are made up of only one element. If you could break silver into its smallest possible parts, you would have one tiny atom of pure silver. An atom has smaller parts that make up its structure. The nucleus, or center of the atom, has a combination of protons and neutrons. Protons have positive electric charges, and neutrons have no charge. The number of protons in a nucleus is unique to each element. The number of protons is an element s atomic number. An atom also has electrons. Each electron has a negative charge, and atoms can lose or gain electrons without changing the element. Some electrons can be shared with other atoms. Scientists use powerful microscopes to look at parts of matter that are too small to be seen with other microscopes. Many substances are not pure. Instead they are made up of several atoms from one or more elements. When atoms combine, they form molecules. A molecule is the smallest possible part of a substance made from more than one atom. It has the properties of that substance. A molecule can have atoms from one element or atoms from several different elements. The air we breathe has different molecules. The oxygen molecules in the air are groupings of two atoms of the same element. Other gases in air, such as carbon dioxide, have atoms of different elements. Scientists today have come a long way in their understanding of atoms and matter. They have developed technologies that help them make images of atoms and molecules. These images show that atoms and molecules are often well-ordered in a grid-like pattern. 6 7

6 The Periodic Table of Elements The periodic table of elements is a tool for organizing the known elements. The table starts with the smallest atomic number in the first row and increases from left to right. Each column in the table organizes elements by shared chemical properties. You can predict the properties of an element if you know which column it is in. Each element has a short symbol with a capitalized first letter. These symbols are used in chemical formulas. For example, the H stands for hydrogen and Ca stands for calcium. Periodic Table of Elements Each element has a unique number of protons and electrons. They give each element its properties. Scientists sort elements into three groups according to their properties: metals, nonmetals, and metalloids. Metals are often good conductors of electricity, are solid at room temperature, and are ductile, meaning they can be stretched without breaking. Nonmetals are identified by their brittleness, their inability to conduct heat or electricity well, and their tendency to break if stretched. The third group, metalloids, includes elements that share properties of metals and nonmetals. Metals Metalloids (semimetals) Nonmetals 8 9

7 Using the Periodic Table The periodic table is a useful tool for understanding elements, and it is full of information about each one. You only need to know how to read it. The block for titanium, shown below, shows you the type of information you can find about any element in the periodic table. Rows show increasing atomic weight, while columns show similar properties. The table comes together in a regular pattern, so you can predict an element s properties based on its location. Close-Up: Titanium Each column in the table is a group or a family. Each family includes elements with similar characteristics. They react with substances in similar ways. Group 1 includes metal elements that react strongly with water. Hydrogen is an exception; it is a gas. Its atomic structure is similar to other elements in its family. But its chemical properties are different. Rows in the periodic table are periods. They are not grouped by similar characteristics. The element farthest to the left is very reactive. The elements become less active as you move to the right. If you look at the groups below, the color of the blocks indicates that the metallic elements on the left are very reactive. The nonmetals on the right are less active. Atomic Number: 22 Symbol: Ti The elements on the far left of the periodic table are very reactive. Name: Titanium The elements on the far right of the periodic table are the least reactive. Titanium is a strong metal that is very light

8 Properties of Metals You have read about metals and may already know some important things about them. Have you ever noticed that most metals are shiny and can bend without breaking? Reflectivity and malleability are properties many metals share. All metals are also solid at room temperature, except for mercury. At room temperature, mercury is a liquid. Metals also share conductive qualities. A good conductor is a material that lets heat and electricity travel through it. Metals are ductile so they can be made into wire. These properties make metals very useful for wiring your home and electrical devices. Many common metals are pure elements. Nickel, iron, and copper are all pure elements. Mixed Metals Many metals are not pure elements. When two or more metals are mixed together, a metal alloy results. Mixing metals together gives the alloy new and different properties. For instance, when carbon and iron mix together, the resulting steel alloy is much stronger than iron alone. Brass, another common mixture made from copper and zinc, is less malleable than copper and prettier than zinc. Musical instruments made of metal, such as trumpets, saxophones, and tubas, are often made of brass. Brass is an alloy of copper and zinc. It has different properties than copper and zinc. nickel iron copper 12 13

9 Compounds When two or more elements combine, they form a compound. The compound has different properties than the elements within it. For example, water is made up of two hydrogen atoms and one oxygen atom. Both hydrogen and oxygen are gases that you can t see, touch, or hold at room temperature. When they combine to form the compound water, you can pour it, boil it, and freeze it. Remember the letter symbols from the periodic table? Compounds have formulas that use these symbols. The formula tells how many atoms of each element make up the compound. The formula for water is H 2 O. H is the symbol for hydrogen, and the 2 tells you how many hydrogen atoms are in the compound. There are no numbers after the O for oxygen, so there is only one atom of oxygen in the formula. Water always has twice as many hydrogen atoms as oxygen atoms. Oxygen, hydrogen, and carbon combine to make sugar. = oxygen = hydrogen = carbon hydrogen oxygen hydrogen Hydrogen and oxygen can join with other elements to create completely new compounds. Oxygen, hydrogen, and carbon join to make sugar. This crystal has little in common with oxygen and hydrogen gas, or the solid carbon found in coal. Elements react differently depending on what they combine with. Sodium combined with chlorine reacts to form table salt. Sodium combined with water creates a violent reaction of sodium hydroxide and hydrogen gas. Compounds make up much more of the substances on Earth than pure elements. A very common substance, water, is a compound that makes up about 60 percent of your body

10 Salt Compounds Many compounds form by sharing electrons, but there are other ways for compounds to form. Salts are compounds made up of particles held together by oppositely charged atoms. Particles with more electrons than protons are negatively charged. Particles with more protons are positively charged. Opposite charges attract and pull the particles together. Most salts share two properties: they are made up of one metal and one nonmetal element, and they can form crystals. Brittle crystals develop when particles arrange themselves in a regular pattern. Common table salt is just one of many types of salt that have these properties. Each crystal of salt has an organized pattern. sodium chlorine Salts can form when chemicals called acids and bases combine. Hydrochloric acid is a highly dangerous acid. When it combines with sodium hydroxide, a dangerous base, they form sodium chloride and water. The salt is dissolved in the water, but salt crystals form if the water evaporates. When hydrochloric acid or sodium hydroxide is mixed with metals, the result is a violent reaction. Acids and bases can be poisonous and corrosive. They can burn your skin. It s important to be very careful while handling chemicals. Never put any chemicals near your face or in your mouth during science experiments. Even though sodium chloride is a harmless salt, many salts are actually poisonous. Sodium hydroxide (left) and hydrochloric acid (right) react in violent ways (when combined with magnesium and zinc pieces, respectively)

11 What can salts do? Salts, as you already know, are made up of metal and nonmetal elements. They form into a regular pattern of brittle crystals. They are also resistant to melting until they are heated at a very high temperature. Even though salt is resistant to heat, it dissolves very easily in plain water. If you continue to pour salt into water, it will reach a point where it stops dissolving. When salts dissolve in water, they make the water an excellent conductor for electricity. Salts dissolve in water. At some point, the salt will no longer dissolve no matter how much you stir. Once elements combine to form salts, the salt has very different properties than the elements that went into it. The photos below show how copper combines with other substances to form salts. When copper is combined with sulfur and oxygen, copper forms a blue salt. When combined with chlorine, it forms a green salt. Neither of these salts looks like copper, nor can they be made into wire or bent into different shapes. They are now brittle crystals. On its own, sodium is a soft metal that reacts explosively with water. When combined with the poisonous yellow gas chlorine, the two create the safe little crystals you recognize as table salt. pure copper copper + sulfur + oxygen copper + chlorine 18 19

12 Separating Mixtures Not all elements bond together to form compounds. A mixture is different from a compound. You know that compounds can have different properties than the elements that form them. In a mixture, the different elements do not bond together. They keep their own properties. Think of it this way: if you make a mixture of raisins with your cereal, the cereal does not change color or flavor, and the raisins don t change color or flavor. They keep their individual properties. In a mixture such as cereal and raisins, the substances keep their own properties. Think of a mixture of sand and water. How would you separate the two? The sand does not dissolve in water, so you might try pouring the mixture through a coffee filter. The bigger sand particles won t be able to squeeze through the filter. The water particles will drip right through. In order to separate mixtures, it helps to know some of the properties of the mixed substances. Knowing that sand has bigger particles than water helps you decide to use a filter. What about sand mixed with iron filings? Both particles are about the same size, but do they have other properties? Iron is a metal, and it is attracted to magnets. The rest of the sand is not. A good way to separate iron from the rest of the sand would be to use a magnet. Magnetism is a physical property of iron. This allows it to be separated from the sand with a magnet

13 Solutions When you pour sand into water, the sand particles sink to the bottom. Other substances dissolve when mixed together, such as salt in water. Instead of sinking to the bottom, the salt spreads out evenly in the water. When a mixture has particles spread out evenly like this, it is called a solution. A solute is a substance that dissolves in a solution. Think about salt and water. Salt is the solute. Water is the solvent, or substance in which the solute dissolves. Water is an excellent solvent for many different solutes. Solubility is another physical property. Solubility describes how much of a substance will dissolve in a solvent at a certain temperature. You can still separate these mixtures, but you may have to heat or cool the solution to remove the solute. This is a dilute solution. More solute could dissolve in this solution. This is a concentrated solution. It has much more solute compared with the amount of solvent. Chromatography When you see a glass of green liquid, you can be pretty sure it s not a glass of water. There is probably a solute in it. How can you know for sure? The process of chromatography uses a substance s solubility to separate it from other substances. Police departments use this process to identify different substances. Paper chromatography works like this: the experimenter puts a dot of the substance on a strip of paper. One end of the paper is placed in water or isopropyl alcohol. This solvent moves up through the paper. When it reaches the solute, the solvent pulls the colored parts, called pigments, up the paper. If a pigment is very soluble, it will travel high up the paper. When the paper dries, you have information about that substance. If there are two or more obvious colors on the paper, your substance was not a pure element. Chromatography can be used to identify different substances, such as pigments

14 Glossary atom atomic number chemical property compound element the smallest particle of an element with the same properties of the element the number of protons in the nucleus of an atom; the single most important property of an element any property of a material that describes how it changes into other materials a kind of matter made of a chemical combination of two or more elements one of more than 100 basic kinds of matter that cannot be broken into smaller pieces through physical or chemical processes What did you learn? 1. What are some physical properties of elements? 2. What is the relationship between an element and an atom? 3. How is a molecule different from a compound? 4. Choose an element from the periodic table on pages 8 and 9. What do you want to know about it? Write four questions you would like to have answered. Using the information on your element s block, try to answer your questions. Write a paragraph about your element using the facts and details you have discovered. Explain how you found the information as you write. 5. Make Inferences Pick three objects in your classroom. Just from looking, touching, and smelling, what can you infer about them? Where do you think they would belong on the periodic table if they were pure elements? What led you to make your inferences? molecule physical property solution the smallest part of a substance made from more than one atom that still has the properties of that substance any property of a material that can be seen or measured without changing the material a mixture in which substances are spread out evenly and will not settle 24