Chapter 2 Objectives PDF

CHAPTER 2 OBJECTIVES » Classify different forms of matter. » Explain why energy is important in chemistry. » Explain the role of energy in changes of Chapter 2 state. MA...

CHAPTER 2 OBJECTIVES » Classify different forms of matter. » Explain why energy is important in chemistry. » Explain the role of energy in changes of Chapter 2 state. MATTER » Analyze a mixture on the basis of the component properties to determine how it can be separated into its parts. OVERVIEW On a clear night in 1572, Danish astronomer fusion. At this point, a supernova occurs and pro- Chapter 2 is foundational for your students, Tycho Brahe had the opportunity of a lifetime: he pels both energy (up to billions of times the en- though it mostly reviews concepts and terms noticed a “new star” in the sky. Over the following ergy of the sun) and matter (the first twenty-six two weeks, the star grew brighter. Surprisingly, elements) into space. that they have studied in earlier science within two years the star had faded Along with these elements, the su- courses. A clear understanding of matter’s from view. We now know that Tycho pernova ejects billions of neutrons. Brahe had observed a supernova, Iron can capture these neutrons and composition, physical and chemical proper­ the explosive event that marks the form higher mass elements. Secular ties, and changes in response to energy is end of the luminous phase of a star’s existence. scientists now believe that all of the other naturally occurring elements critical for this course. The kinetic-molecular While a supernova is of immense have formed through a series of theory is a foundation on which other chemi­ interest to astronomers and astro- neutron capture and nuclear decay physicists, some chemists are also events. The elements formed from cal theories are built. interested in these events. Many those supernova events in the past chemists believe that all of the ele- supposedly then went on to become ments in nature have come from the nuclear re- planets, chemical compounds, and even living 2.1 THE CLASSIFICATION OF MATTER actions in stars. Scientists understand that a star’s organisms. So are we just stardust? energy is produced by nuclear fusion. Initially, » Organizing Our Study of Matter hydrogen nuclei fuse to form helium. As a star 2.1 The Classification of Matter 21 » Physical Properties and Changes ages, the nuclear fuel and products change un- til it produces iron. Iron has the most stable nu- 2.2 Energy and Matter 31 2.3 The States of Matter 40 » Chemical Properties and Changes cleus of any element and can’t undergo nuclear » Pure Substances and Mixtures » Elements » Compounds 2.2 ENERGY AND MATTER » Work and Energy » Forms of Energy » Conservation of Mass-Energy » The Law of Entropy » Thermal Energy, Temperature, and Heat The Chapter opener image is a photograph » Measuring Temperature and Thermal of the Rosette nebula, a cloud of ionized Energy hydrogen atoms that secular scientists think may be a location of recent star 2.3 THE STATES OF MATTER formation. » Common States of Matter » Changes of State » Final Thoughts on Origins LAB ACTIVITIES Lab 2A: Needle in a Haystack—Students use physical properties to separate a mix­ ture into its components. Lab 2B: Zebroids, Wolphins, and Ligers, Oh My!—Students classify substances on the basis of their properties. 20 Chapter 2  SECTION 2.1 OVERVIEW 2.1 THE CLASSIFICATION OF MATTER Essential Question I n the Chapter opener you read a current hypothesis in which secular scientists attempt a naturalistic explanation for the origin of matter. While their model explains most observations about matter, they have QUESTIONS » Where did matter come from? Isn’t all matter the same? » What are some properties of no observable evidence for its origin, but they accept their model on faith. According to the Bible, everything was created out of nothing by matter? » What are the different types of Objectives God. A creation model for the origin of matter also explains almost all our observations about matter. We accept the biblical account on faith, matter? » Where did the names and symbols » 2.1.1 Evaluate differing views about the and the Genesis account is the foundational truth of a biblical under­ for elements come from? » What do chemical formulas tell origin of matter. BWS standing of chemistry. Organizing Our Study of Matter us? TERMS » 2.1.2 Compare physical and chemical T he world that God spoke into existence contains an amazing va­ physical property physical properties. riety of material. Just look around you to see the different types of change chemical property materials and the things made from them: paper, wood, metal, plastic, computers, and cellphones. And these are just a few of the many forms chemical change pure substance mixture heterogeneous mixture » 2.1.3 Define pure substance and mixture. homogeneous mixture element that matter takes. Scientists have identified millions of different mate­ rials, both natural and manmade. Some materials may be in the same atom chemical symbol molecule compound chemical formula » 2.1.4 Organize matter into general form as they were when created. But nearly all accessible categories on the basis of natural minerals have been partially or even significantly modified by the Genesis Flood. Humans also rework natu­ Isn’t all matter characteristics. ral materials into other useful materials. the same? Recall from Chapter 1 that matter is defined as any­ » 2.1.5 Explain where chemical symbols thing that has mass and takes up space. With so many dif­ ferent types of matter, it would be good to organize our study of matter came from. with a good classification system. Although there are different ways that we could classify matter, this textbook divides it into two major » 2.1.6 Interpret chemical formulas. categories: pure substances and mixtures. We can make distinctions between these two categories on the basis of the physical and chemical properties of matter. Resources Case Study: Understanding Trihydrogen Demonstrating Reactivity Properties are the distinguishing characteristics of matter. Scientists Mini Lab: Paper Chromatography; divide these characteristics into two Lab 2A: Needle in a Haystack—Separating classes: physical and chemical. Mixtures; Lab 2B: Zebroids, Wolphins, and Ligers, Oh My!—Classifying Matter ENGAGE CLASSIFICATION Guide a class discussion to activate prior knowledge by asking students to identify things that we classify. Students may think of, for example, books in the library, types Matter 21 of movies, and types of animals. Pick one of the topics that the students suggest and have them explain how those things are classified. For example, movies are classified by genre (drama, comedy, documentary, action, sci-fi). They are also classified by ratings (G, PG, PG-13). Some students might mention live-action, animated, and CGI. Ask students why we classify things. Use this discussion to introduce the concept of classifying matter. IDENTIFYING MATTER Guide a class discussion to activate prior knowledge by having students quickly name items defined as “matter” in the class­ room. Have them review the definition of matter from Chapter 1. Matter 21  INSTRUCT PHYSICAL PROPERTIES AND CHANGES PHYSICAL AND CHEMICAL A physical property is any property of matter that can be observed or » What does it look like? measured without altering a substance’s chemical composition. Color, PROPERTIES shape, texture, state of matter, odor, and taste are examples of properties » How much is there? » How closely is it packed together? that we can observe without changing the composition of the material. Quiz students to assess prior knowledge Other common physical properties of matter follow. by asking them what they think we mean by the term physical properties. They should Density Malleability quickly think of describing how something The amount of matter packed into a given Materials that can be hammered easily into shapes volume is its density. Dense objects have a lot or thin sheets are malleable. This property is possible looks (e.g., size, shape, color, texture). Stu­ of matter packed into the space they occupy. because the connections between the particles that dents should recall from physical science that Less dense objects have less matter in the make up these ma­ same space. Density will be explored further terials are strong but these are properties that can be observed in Chapter 3. allow some move­ without changing the substance into another ment. Most metals are malleable. Thirty substance. For example, the temperature of grams of gold can gasoline can be measured without changing Usually rocks sink be hammered out to cover thirty square because they are it into a different substance. denser than wa- meters—more than ter, but pumice the surface area of In contrast, chemical properties show how —a volcanic rock the family car! —floats due to a substance reacts with other substances air trapped or acts under certain conditions. When we within its pores. observe a chemical property, a substance Ductility becomes something new. Materials that can be drawn into long, thin wires are ductile. Ductility is another property of most metals. The same proper­ DEMONSTRATING REACTIVITY ties that make gold the most Conductivity malleable metal also make it the Use this demonstration to show the dra­ The ability of a material to transfer heat or most ductile. A single ounce of gold can be drawn into a fine matic and messy nature of some chemical electricity between its particles represents its wire that is eighty kilometers conductivity. For example, the handle of a changes. metal spoon left in a hot pot on a stove be­ long. Copper and aluminum are also extremely ductile. comes hot, but the handle of a wooden spoon This demonstration involves concen­ does not. The metal conducts heat easily; the trated sulfuric acid, so you will need to take wood does not. Silver is the most electrically conductive metal, but because of silver’s high proper safety precautions. Be very careful cost, we usually use copper for electrical wiring. when handling sulfuric acid because it is a strong acid! The properties listed here are all properties that do not Physical changes are any changes in the appear­ change no matter how much or little of the material is ance, shape, or state of matter in a material that If you don’t have access to sulfuric acid, are present. For example, a material is ductile regardless of how do not cause a change in its chemical compo­ uncomfortable working with it, or don’t much material there is. Properties such as these that do not sition. Think about a ductile material like copper. depend on the amount of material present are called inten- As we draw copper into a long wire, it changes have access to a vent hood, you can use an sive properties. Other properties, like mass and volume, do shape, but it is still copper. Boiling is a physical online video of this demonstration. change depending on how much of the material is present. change in which a material changes from its liquid These properties are called extensive properties. state to vapor, but its identity is not altered. The reaction decomposes sugar into water 22 Chapter 2 vapor and pure carbon. Materials: 150 mL glass beaker containing 30 g table sugar, 30 mL concentrated sul­ Cleanup: Remove the carbon column and To avoid confusion, stress that a chemical furic acid, stirring rod, nitrile gloves, goggles place in a bucket of water. Neutralize it with change produces a new material, while a (for everyone), vent hood, sodium bicarbon­ sodium bicarbonate. Once neutralized, the physical change does not. A physical change ate, bucket, and water for cleanup solid can be thrown in the trash and the is a change in the appearance of a material; Preparation: Before students arrive, have water can be poured down the drain. The it does not change the composition of the the materials, except gloves and goggles, beaker can be cleaned with acetone. particles. A chemical change always changes in the vent hood. Having a heat-resistant the composition of a substance, which often tray under the demonstration will help with causes a change in appearance. PHYSICAL AND CHEMICAL cleanup. PROPERTIES All chemical reactions involve one or more Presentation: Pour the concentrated sul­ chemical changes. We have not included the furic acid into the beaker containing sucrose Use the infographic to dispel misconcep­ term chemical reaction as a vocabulary term (table sugar). Stir the mixture so that it is tions by showing the main point of this in this chapter. It will be defined later and is completely mixed. The beaker will get very page spread: the difference between physi­ a central concept of chemistry. hot. Step back and watch the reaction (it cal and chemical properties and between might take a few minutes). physical and chemical changes. 22 Chapter 2  PHYSICAL AND CHEMICAL CHEMICAL PROPERTIES AND CHANGES PROPERTIES Chemical properties are those properties that describe how matter acts in the presence of other materials or how it changes composition under certain Use this formative assessment to check conditions. Some examples of chemical properties are reactivity, flammability, students’ understanding of physical and and toxicity. chemical properties. 1. What is a physical property? (a prop­ Reactivity erty that describes a substance’s physical Substances can range from being completely stable to being highly characteristics and that can be observed reactive depending on the presence of other substances or particular con­ ditions. Sodium is stable when stored in oil, but it will react vigorously without changing the chemical compo­ in the presence of water. Water itself is an example of a material that sition of the substance) behaves differently under different conditions. Water, typically very stable, will decompose in the presence of electrical energy. 2. What is a chemical property? (a property that describes how a substance interacts with a second substance or how it acts under certain conditions; a property that Flammability when observed causes a change in the While reactivity relates to how chemical composition of the substance) something responds to different substances or conditions, flam­ Toxicity 3. Compare malleability and ductility. mability is all about whether a substance will burn or not. We Some substances have an adverse effect (Malleability is how easily a material is can burn hydrogen, demonstrat­ on living organisms. Toxicity indicates hammered or pressed into sheets, while ing that it is flammable. When how much damage a substance will do tested for flammability, hydro­ to a particular organism. Toxicity is often ductility is how easily it can be drawn into gen “changes” into water vapor reported as its LD50 rating. LD stands for a wire. Both are physical properties.) through a chemical change. Also, the lethal dose, and the LD50 of a partic­ flammability can depend on vari­ ular substance is the amount that would be expected to kill half an exposed 4. A classmate tells you that oxygen is ous conditions. For instance, metal zinc is not flammable unless it is in population. Arsenic is a metalloid that is reactive. Is he correct? (He may be. Re- powdered form. toxic to humans in very low doses. activity depends on other substances and conditions. Oxygen may be reactive with a particular element under certain con- ditions. With a different element or under When a substance undergoes a change in which its other conditions it may be nonreactive.) chemical identity changes, we say that it has experi­ enced a chemical change—also called a chemical reaction. When the composition of the substance changes, so do its chemical and physical properties. When iron rusts, it undergoes a chemical change. The iron particles combine with oxygen particles to form iron(III) oxide—rust. Not only is rust a new substance; it also has different properties from oxygen or iron. Matter 23 DIFFERENTIATED INSTRUCTION Active Learning: Physical and Chemical Properties Lead students through an active learning To do the same activity from students’ seats, activity to help them internalize the con- provide each student with signs for choices cepts of physical and chemical properties. PP, PC, CP, and CC, one for each term. Have Have labels for “physical property,“ “physical them hold up their answer to each descrip­ change,“ “chemical property,“ and “chemi­ tion. You can also use technology to do the cal change“ posted around the room. Give same activity by using a classroom response descriptions that fall into each category and system, survey website, or quiz website. have students move to the proper location in the room. Then ask select students to explain why they chose the location that they did. Matter 23  PURE SUBSTANCES AND MIXTURES Ask these formative assessment questions Pure Substances and Mixtures Scientists use chemical and physical properties to organize matter into pure substances and mixtures. to check students’ understanding of pure substances and mixtures. Pure Substances A pure substance consists of only one type of matter. 1. What is a pure substance? (a substance Scientists further categorize pure substances into elements and compounds. While elements cannot be broken down that is made of particles of one type of by chemical means, compounds can be broken down into matter) elements through chemical changes. You will learn about elements and compounds later in this section. 2. How can we further categorize pure substances? (as elements and com- Mixtures pounds) A mixture is two or more substances that are physically combined in a variable ratio. There are two types of mixtures—heterogeneous and homogeneous. 3. What is a mixture? (A mixture is a physi­ cal combination of two or more sub­ stances in a changeable composition.) A heterogeneous mixture consists of two or more materials 4. How can we categorize mixtures? (as in distinct regions, called phases. heterogenerous and homogeneous) Consider oil and water: if left undisturbed, these materials will separate into distinct regions, the 5. What is a heterogeneous mixture? (a oil bubbles and water (see image mixture with distinct regions or phases) at left). Many salad dressings contain a mixture of vinegar and oil. No matter how vigorously you shake the dressing, a microscopic examination will always show two separate phases—oil and vinegar. Because of the different phases, heterogeneous mixtures typically have a nonuniform appearance. Scientists further categorize heterogeneous mixtures as col­ loids and suspensions depending on the size of the dispersed parti­ cles. We will discuss colloids and suspensions in Chapter 14. A homogeneous mixture has only a single phase, which gives it a uniform appearance throughout. Homogeneous mixtures are also called solutions. If you dissolve sugar in water and stir it until it completely dissolves, it appears as a single liquid phase—sugar water. Likewise, when molten gold and silver are thoroughly mixed, a single phase of white gold results. Air is Dissolved CO2 gives an example of a gaseous solution. Notice the soda, which is a solution, in soda its fizz. the bottle at left. While it is a mixture, there is only one liquid phase visible in the bottle. 24 Chapter 2 24 Chapter 2  Separating mixtures Since mixtures are combined physically, they can be separated by physical means. The specific method used for separating a mixture will depend on the physical properties of the substances that make up the mixture. Some common methods of separating mixtures include filtration, decanting, and distillation. Filtration When a mixture consists of a fluid and another substance with significantly larger particle size, we can separate the substances by filtration. As the small fluid particles move through the filter, the filter blocks the larger particles. Many of us are thankful for the common coffee filter that allows the liquid coffee to pass through while trap­ ping the larger coffee grounds. Decanting Distillation A heterogeneous mixture of two liquids or a liquid and a solid can If the substances in a homogeneous mixture have sufficiently different be separated by decanting. We boiling points, we can separate them by distillation. In this process, the decant a mixture by pouring the mixture is heated until the lower boiling point is reached. As the mix­ less dense material off the top ture boils, it is collected in a separate container as a pure substance. The of the denser material. Tradition­ mixture is further heated until all the individual substances are separated. ally, decanters were vessels from In the setup below, the mixture in the flask on the left will be heated to which wine was decanted, leav­ the boiling point of one component. That component is condensed in the ing solid sediments behind. central part of the apparatus and collected in the flask on the right side. Distillation is commonly used to separate hydrocarbons out of crude oil or to produce alcohols. We regularly deal with mixtures in our daily lives, but most of our study of chemistry will involve pure substances. Matter 25 Matter 25  MINI LAB APPLY MINI LAB: PAPER CHROMATOGRAPHY PAPER CHROMATOGRAPHY Use this mini lab to have students apply Chromatography is another method for separating a mixture. In paper chromatography, a sample is placed on chromatography paper (the Is the ink in a marker their knowledge of separating mixtures stationary phase). The paper is then dipped into a solvent (the mobile a mixture or a pure to analyze the ink from markers by using phase). The solvent dissolves the sample. If the sample is a mixture, substance? the solvent will separate the sample. The components of the mixture, chromatography. This is an essential labora­ as well as the degree of separation, enable a scientist to identify the tory skill that will demonstrate a method of mixture. separating mixtures. F On the lines you just drew, put a dot EQUIPMENT with each of the different markers that beaker, 300 mL Answers you have. watch glass G Hang the papers on the clip so that the 1. The paper remains stationary, but the paper is in the water but the marker paper clip solvent moves up the paper as the dot is not under the water. Cover the chromatography beaker with the watch glass. paper paper absorbs the water. 1. Why do you think the paper is the water-based 2. Answers will vary. Many students will stationary phase and the solvent is the markers (3) mobile phase? find that the green marker and black H Remove the papers when the solvent marker are mixtures, while red, blue, stops moving upward or before it and yellow are often single colors. reaches the top of the paper. Mark the highest point of solvent travel. 3. Answers will vary. Students will typi­ Conclusion cally find that blues travel the farthest Procedure 2. Which of the marker colors was made distance and yellows the shortest. A Straighten the paper clip so that it can up of a mixture of colors? span the beaker. 3. Did all the colors travel the same dis­ 4. The colors travel due to adsorption tance up the paper? B Cut three 1.5 cm wide strips of chroma­ forces. The lesser the degree of attrac­ tography paper. The paper should be Going Further tion between the component and the slightly longer than the beaker height. 4. Why do you think the different colors traveled different distances? paper, the farther the component will C Pour approximately 30 mL of water into the beaker. Scientists use a measure called the Rf value travel with the solvent. to compare the degree of separation of the D Fold the top of each piece of chroma­ different components. They calculate the 5. Since the Rf value is quantitative, a tography paper so that the bottom of Rf value for a component by dividing the the paper will be just hanging in the scientist can compare the Rf values of water. Don’t allow the paper to get wet. distance the component traveled by the distance the solvent traveled. different components. Scientists can E With a pencil, draw a line 1.5 cm above 5. Rf values provide quantitative data for also compare the experimental Rf val­ the bottom edge of the paper. the analysis of chromatography. How is ues with values of a known substance, this beneficial to scientists? giving them the ability to identify the specific components in the mixture. 26 Chapter 2 26 Chapter 2  C IS FOR CARBON Guide the students in a visual analysis us­ Elements ing the periodic table to solidify their under­ I n the description of the Garden of Eden in Genesis 2, gold is mentioned. Throughout the Bible, there are numerous references to many materials (such as silver, sulfur, tin, and iron) that today we standing of chemical symbols. Have them find other elements that begin with C. Note know as elements. Scientists discovered many other elements shortly after the rise of modern science in the 1800s. And other elements have Sulfur rock and gas (background); how the symbols relate to the sounds and recently been synthesized in the laboratories of nuclear physicists. An sulfur atomic structure (below) spellings of their names, as in Cl for chlorine, element is a pure substance that cannot be broken down into a sim­ pler substance by ordinary chemical means. Each element has unique Ca for calcium, and Cr for chromium. There chemical and nuclear properties. Today there are 118 known elements that are represented on the periodic table (see table below). are a few exceptions, such as Cu for copper. We also define an element as a pure substance that consists of Ask students whether they have a thought only one kind of atom. For example, a piece of pure copper metal is made up of only copper atoms. An atom is the smallest particle that about where Cu for copper came from. makes up an element and is capable of chemical interactions. An atom consists of a nucleus containing positively charged protons and, in most cases, uncharged neutrons. A cloud of negatively charged electrons ELEMENT MEMORIZATION NOTE surrounds the nucleus. When the number of protons and electrons in an atom are equal, the atom is electrically neutral. However, when they are There are a number of philosophies regard­ out of balance, the atom has a net electrical charge and is called an ion. ing the benefits of having students memo­ rize portions of the periodic table. Some teachers see memorizing the table as a vital part of a chemistry course, while others feel Each element has a special chemical symbol that represents its name. The first letter of the name of the element often serves as that students need only be familiar with its symbol (e.g., H for hydrogen, N for nitrogen, and O for oxygen). the table so that they can use it efficiently. Regardless of your position on this topic, there is a benefit in requiring students to be familiar with the most commonly used elements. The periodic table is the subject matter for Chapter 6, but you may want to have your students get a head start on memorizing however much of it you expect them to. Frequently the names of more than Since the single letter C stands for car­ Consider the symbol for the element one element have the same first letter. bon, we use Ca for calcium and Cd for cobalt: Co. If written carelessly as CO, To avoid confusion in these cases, we cadmium. We always uppercase the the referenced element could be use a second, lowercase letter. The first letter of an element’s symbol, and confused for the compound carbon second letter is usually related to the the second letter if present is always monoxide, a poisonous gas found in sound of the element’s name. lowercase. Careless writing of symbols automobile exhaust. can result in serious errors. Matter 27 MISCONCEPTION ABOUT ATOMS PRINTABLE PERIODIC TABLE Lead a class discussion to eliminate stu­ The periodic table is a vital resource for dents’ misconceptions about the definition students. A periodic table is provided on of an atom. An atom of an element is not the the last page spread of the Student Edition. smallest particle that exhibits all the physical Some teachers prefer to print copies for and chemical characteristics of that element. students. There are many excellent printable Individual atoms of each element do have periodic tables on the internet that display a unique chemical and nuclear properties, but variety of data. they do not exhibit all the physical proper­ ties described earlier in the section. Many of these properties, like color, are the result of interaction between large numbers of the element’s atoms. For example, a gold atom does not have a gold color. Matter 27  The particles of elements in their natural state may consist of individual atoms or groups of atoms. If an element occurs naturally as individual atoms, the element is called a monatomic element. Mona­ tomic elements are rare because most atoms tend to bond with one or more other atoms. Examples of monatomic elements are neon, argon, monatomic element and xenon. Elements whose atoms naturally bond into two­atom units are called diatomic elements. The seven diatomic elements are hydro­ gen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine. Ele­ ments whose particles are normally composed of groups of more than two identical atoms are called polyatomic elements. For instance, sulfur often occurs in the form of eight atoms bonded into a single unit. Oxy­ gen can also exist as ozone high in the atmosphere. The subscript number in each chemical symbol shown at left indicates the number of atoms of the element that are present. If there Dinitrogen (N2) is no subscript, we understand that the element exists in the form of diatomic element uncombined atoms. Distinct groups of atoms bonded together are called molecules. Molecules may consist of atoms from one element or from different elements. Molecule diamond molecular structure made up of carbon atoms Ozone (O3) polyatomic element 1 2 You can easily find the seven diatomic elements on a H periodic table if you remember the Hydrogen Seven. He 3 4 Remember hydrogen, then go to element number 7 5 6 7 8 9 10 Li Be (nitrogen) and make a large number 7 on the periodic B C N O F Ne 11 12 table (oxygen, fluorine, chlorine, bromine, and iodine). 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 28 Chapter 2 28 Chapter 2  UNDERSTANDING TRIHYDROGEN Element names come from many different sources. Lead a class discussion using this case Latin names serve as the basis for many of the symbols for some elements that were known in ancient times. study to expand students’ thinking about For example, cuprum, the Latin name for copper (Cu), the concepts in this section. means “from the island of Cyprus” and is the source for its symbol. Elements are named after many things. Answers to Questions to Consider color: iridium (Ir) from the Latin for “rainbow” 1. three atoms of hydrogen (p. 28) people: curium (Cm) for Pierre and Marie Curie, early researchers of radioactivity 2. An ion is an atom or molecule with a net places: californium (Cf ) for California nonzero charge. (p. 27) heavenly bodies: helium (He) from helios, the Greek word for “sun” 3. While the presence of trihydrogen is of critical importance in the secular theory miscellaneous words: bromine (Br) from the Greek word for “stench” for the origin of matter, its presence has Today it is generally accepted that whoever no bearing on a creationist view of the discovers a new element has the honor of naming it, origin of matter. According to a cre­ subject to the approval of the International Union ationist view, trihydrogen was created of Pure and Applied Chemistry (IUPAC), an inter­ national organization responsible for standardization during the Creation event and has been in chemistry. The periodic table of the elements in the in the interstellar medium since Day 4. back of this textbook displays the symbols for all the CASE STUDY known elements. Compounds UNDERSTANDING TRIHYDROGEN A pure substance that consists of two or more elements chemically combined in a fixed ratio is called a compound. Some compounds form distinct Trihydrogen is an interesting molecular ion consisting of three hydrogen atoms held together by a single chemical bond. Initially discovered over one hundred particles—molecules—while other compounds form years ago in 1911, trihydrogen has recently become of vast crystalline arrays with repeating arrangements particular interest to astrochemists. In the early 1960s of ions. As you can imagine, there are many more it was hypothesized that trihydrogen could exist in compounds than elements. Just as chemical symbols the interstellar medium, the material located between are used to represent elements, chemists use chemical stars. During the 1990s its existence in the interstellar formulas to represent the millions of kinds of com­ medium was confirmed, and by the early 2000s it was pounds. The chemical formulas are made up of the noted that it existed in large quantities. Today natural- chemical symbols for each element present. Numbers istic scientists believe that trihydrogen was a key written at the lower right of a chemical symbol are material in the transition from the origin of matter to called chemical subscripts. They indicate the number the matter we see today. of atoms or groups of atoms in a chemical formula. Questions to Consider A molecule of water contains two hydrogen atoms and a single oxygen atom and so is written H2O (the 1. Of what is trihydrogen made? 1 for oxygen is assumed). When a subscript follows a 2. What is an ion? group of symbols that are surrounded by parentheses, 3. What does the existence of trihydrogen in the it refers to the entire group. The formula Ca(HCO3)2 interstellar medium imply about the origin of consists of a calcium atom and two HCO3 groups, for matter? a total of one calcium atom, two hydrogen atoms, two carbon atoms, and six oxygen atoms. Notice that the subscripts act very much like exponents in mathe­ matical expressions. The six oxygen atoms comes from the three oxygen atoms multiplied by two. Matter 29 DIFFERENTIATED INSTRUCTION Mnemonic for Diatomic Elements Provide students with the Hydrogen Seven mnemonic device for remembering the seven diatomic elements. Students will need to remember hydrogen, but the other six elements can be found by making a large 7 on the periodic table, starting at element 7 (nitrogen). Matter 29  CRYSTALLINE COMPOUNDS In later chapters, we will discuss crystalline TABLE 2-1 In compounds that form molecules, each molecule has a definite number of atoms. A molecule is the small­ compounds and formula units in greater Some Compounds and Their Formulas est distinct particle of a compound. Therefore, molec­ detail. For now, students should simply be Compound Formula Atoms ular chemical formulas indicate the type and number of atoms of each element present in each molecule. To aware that not every compound is repre­ ammonia NH3 one nitrogen, three hydrogens illustrate this, let’s consider two compounds of oxygen sented by molecules. two irons, and nitrogen. The formula NO represents nitrogen mon­ rust Fe2O3 oxide. This formula tells chemists that each molecule of three oxygens this compound contains one nitrogen atom chemically one sodium, combined with one oxygen atom. Another compound of MOLECULAR FORMULA PRACTICE table salt NaCl one chlorine nitrogen and oxygen is dinitrogen trioxide (N2O3). This compound’s molecule consists of two nitrogen atoms one calcium, Guide students in practice to help them cleansing two hydrogens, combined with three oxygen atoms. Ca(HCO3)2 In compounds that form crystalline arrays, there are understand molecular formulas. Put a series lime two carbons, six oxygens no distinct particles that make up the compound. Since of formulas for different compounds on the twelve carbons, there are no molecules, the chemical formula represents the smallest whole number ratio of the elements that are board and ask them to identify the names of sucrose (table sugar) C12H22O11 twenty­two hydrogens, in the compound and is called a formula unit. Common table salt is a compound of sodium and chlorine ions in the elements included and how many atoms eleven oxygens a crystalline structure. They combine in a one­to­one of each element are represented. Start with water H2O two hydrogens, ratio, so the chemical formula for table salt is NaCl, in­ one oxygen dicating that for every sodium ion there is one chlorine easy formulas like NaOH, CO2, and HCl, then ion. Some common compounds, their formulas, and the raise the difficulty level with examples such atoms that they contain are listed in Table 2­1. as Ba(OH)2, K2SO4, and Mg3(PO4)2. For a real EXAMPLE 2-1: DECIPHERING COMPOUND FORMULAS challenge, give them Na2HPO4∙7H2O (sodium How many atoms of each element are present in each b. No subscript after the magnesium indicates that dibasic heptahydrate). of the following formulas? only one atom is present. The subscript 2 after the nitrate (NO3) group means that two nitrate a. Na2S2O3 b. Mg(NO3)2 c. N3O5 groups are present, for a total of two nitrogen ASSESS Solution a. The subscripts show that two sodium atoms, atoms and six oxygen atoms. c. The subscripts show that three nitrogen atoms two sulfur atoms, and three oxygen atoms are and five oxygen atoms are present. TICKET OUT THE DOOR present. Check for understanding with this summa­ rizing activity. Ask, “Why do we classify 2.1 SECTION REVIEW matter?” 1. What is a physical change? Give three examples of 6. Create a hierarchy chart that relates the terms LAB 2A: NEEDLE IN A HAYSTACK physical changes. compound, element, heterogeneous mixture, homo- geneous mixture, mixture, and pure substance. 2. Differentiate between physical and chemical properties of matter. Give two examples of each LAB 2B: ZEBROIDS, WOLPHINS, property. 7. Why do you think the chemical symbol for potassium is K? AND LIGERS, OH MY! 3. What are the two main classes of matter, and 8. Give the number of each kind of atom in the what characteristics differentiate them? following compounds. Once students have an understanding of the 4. Explain the difference between heterogeneous a. Li2O c. HC2H3O2 material in Section 2.1, they should be ready and homogeneous mixtures. b. Ca(OH)2 d. (NH4)2CO3 to work through Labs 2A and 2B. 5. (True or False) Mixtures can be separated by either physical or chemical processes. 2.1 REVIEW ANSWERS 30 Chapter 2 1. A physical change is a change in ap­ pearance, shape, or state of a material. Examples: crushing, dissolving, hammer­ element or a compound). A mixture is 6. ing into a thin sheet, changing from a physical combination of two or more a liquid to a gas (Other answers are substances in a changeable ratio. (p. 24) MATTER possible.) (p. 22) 4. A heterogeneous mixture consists of 2. A physical property of matter can be de­ two or more materials segregated into termined or observed without altering distinct pieces, regions, or phases (e.g., the chemical composition of the matter. oil and water), which gives the mixture pure Examples: color, hardness, electrical con­ a nonuniform appearance. A homo­ substance mixture ductivity, malleability. (Accept any two.) geneous mixture is a physical combi­ A chemical property can be determined nation of two or more pure substances only through a change to the material in which the individual particles of the substances are uniformly distributed element homogeneous that permanently alters its composition. mixture Examples: reactivity, toxicity, flamma­ throughout the mixture (e.g., salt bility (Accept any two.) (pp. 22–23) water). (p. 24) compound heterogeneous 3. The two main classes of matter are 5. False. Because mixtures are physical mixture pure substances and mixtures. A pure combinations, they can be separated only by physical means. (p. 25) (pp. 24, 27–29) substance consists of only one kind of matter that is chemically combined (an 30 Chapter 2  SECTION 2.2 OVERVIEW 2.2 ENERGY AND MATTER Essential Question Work and Energy How can energy be lost? W e do all sorts of work in our daily lives, like when we rake leaves in the yard, move furniture, or ride our bikes. Work is done anytime QUESTIONS » What forms of energy are there? » What is thermodynamics? Objectives an object moves while a force is applied along its direction of motion. Whenever we do work, we get » Where did energy come from? » Are heat and temperature the » 2.2.1 List and give examples of the six hungry because we have to use energy to do work, same? common forms of energy. and eating replenishes that energy. Scientists de­ » Why are there different scribe energy as the ability to do work. According to this description, energy is something that matter temperature scales? » 2.2.2 State the three laws of thermo­ TERMS has—an ability—just like having a wallet full of energy kinetic energy dynamics in your own words. cash gives you the ability to buy things. The value of potential energy thermal what you purchase with cash should be equivalent to the amount of money you spend. Similarly, there energy thermodynamics law of conservation of mass-energy » 2.2.3 Explain how the origin of energy fits is an equivalence between energy and work done. system heat temperature in with the laws of thermodynamics. exothermic process In fact, scientists use the same dimensional unit to endothermic process BWS measure them—the joule (J). Celsius scale absolute Since energy is the ability to do work, matter moves whenever work is done, and work makes zero Kelvin scale joule » 2.2.4 Compare temperature, thermal changes to the energy in matter. We can energy, and heat. see how closely connected energy and How can matter are. Albert Einstein made this connection even stronger with his energy be » 2.2.5 Explain exothermic and endo­ famous equation, E = mc2. This equation lost? thermic processes and give an demonstrates the equivalence of matter and energy—they are two forms of the example of each. same thing. In the beginning, God spoke every­ thing—matter and energy—into existence. Today » 2.2.6 Explain why the Kelvin scale is we work to increase our understanding of these and other concepts to fulfill the Creation Mandate. called the absolute temperature scale. Resources Worldview Investigation: The Big Bang Demonstrating Entropy Physically, Demonstrating Entropy in Solutions, Demonstrating Thermal Energy and Temperature Wind turbines convert the mechanical energy of ENGAGE moving air into electrical energy. ENERGY Query students in a think-pair-share to pre­ assess their understanding of energy. Have Matter 31 them each write a definition of energy. They should then discuss their definition with a partner. Have some students share their 7. The symbol for potassium is from the answers with the class. This think-pair-share Latin name for potassium (kalium). can also be used later in the section as a (p. 29) formative assessment. 8. a. two lithium atoms and one oxygen You can expand on the engagement activity atom by having students brainstorm different types of energy. b. one calcium atom, two oxygen atoms, and two hydrogen atoms c. four hydrogen atoms, two carbon atoms, and two oxygen atoms d. two nitrogen atoms, eight hydrogen atoms, one carbon atom, and three oxygen atoms (all p. 30) Matter 31  INTRODUCTION TO WORLDVIEW INVESTIGATIONS WORLDVIEW INVESTIGATION Select chapters in the Student Edition include Worldview Investigations. These are THE BIG BANG opportunities for students to investigate You can’t read much about origins in science publi- cations without seeing a reference to the Big Bang a real-world issue in chemistry and view it theory, the currently accepted naturalistic theory through the lens of Scripture. Each one has regarding the origin of the universe. But what exactly does this theory say? There is much misinformation the student produce something that you about what exactly the theory states and implies. can assess. To help you with the assessing Task worldview investigations, rubrics are avail­ Forms of Energy E Your Christian school and a homeschool cooperative nergy is related to the force that matter g