Focus on California 8th Grade Physical Science Textbook Chapter 5 Atoms and Bonding

Chapter i a tad oime more than 100 elements of rumor has distinct properties and a distinct . All forms ! ru an of out ur morn at ( moms . As a bars for this mutant know ( are by two or more different and ma ! urn pounds have properties that are div . femur imm than Students know that atoms and wind by up . sum as the crystal oi ) i av Vang ( ham poly mars know how to use the it to identify elements in simple me organization oi the table is based on the of and relied me oi atoms As a basis ior this Students Imam ( he ( Ins by many . moi , And and ( is made hy asking conducting investigations . As an basis ior and ing he in the three , students should develop awn liens Ind perform . and ( in an I Distinguish between linear and on a graph oi data oi mam ,

Moms and Bonding How do compounds form ?

Check What You Know Water is a compound made from the elements hydrogen and oxygen . How do the properties of water differ from those of the elements that it is made up of ?

Inputs 171 The images shown hem represent some at the key terms in this chapter . Vou can use this vocabulary skill to help you understand the meaning of some key terms in this chapter . Academic Words academic words are words you are likely to meet while reading textbooks . Look for the following words in context as you read this chapter . Word Definition Sentence conduct To allow something to Metal strips on a circuit board ( nun ) travel along or through it conduct electric current . stable . Not easily or quickly Gold is a stable metal that ( suv bul ) 177 changed from one state does not rust or tarnish . to another structure The way in whith parts The outside structure of the ( mint ) 178 at something are put building is at brick and together concrete . symbol A written sign that The symbol for the element bul ) stands for something else oxygen Is . Apply It ! Choose the word that best sentence . is the fit hydrogen . mum

molecule Chapter Vocabulary Section , dot diagram chemical bond Section lodge ) Ion polyatomic ion ionic bond Ionic compound Section my covalent bond molecule double bond triple bond molecular compound polar bond bond Section ) alloy metal ! band 9113 ' i Compare and Contrast When you and contrast , you the and among . You can compare and contrast by using a table , these steps to set up a ( table List the Items to be compared the first column . the to be ( across the top of the ( Complete the ( able by in Information about Eath In this ( you wait learn about ( compounds , such as table salt ( Look at the table . Compounds and Their Component Elements Color I state at Room Temperature Table San White ( Nat ! Sod ry Mute Solid ( Na ) Greenish Gas ( Apply It ! and the ( above to the of those of sodium and After Semen compare the of compounds with those of compounds .

, Models of Compounds I In this ( you will learn how atoms of elements react with one another to form compounds . When they compounds , the atoms be ( ome bonded to each other . In this investigation , you will ( models of ( Your Goal To make models demonstrating how atoms bond in ( compounds and in molecular ( In complete the investigation , you must select appropriate materials to make models of atoms the number of bonds eath atom use your model atoms to compare compounds that contain ionic bonds with compounds that contain covalent bonds follow the safety guidelines in Appendix A Plan It ! Brainstorm with some classmates about materials you ( an use to represent different atoms and chemical bonds . Look ahead In the chapter to preview ( and covalent bonding Think about how you will show that ionic and ( bonding are . You may need to find some small , but highly visible , to represent Be ready to display your models and explain what they show .

Atoms , Bonding , and the Periodic Table ( Standards Focus an Standards Students how to use the periodic table to identify ele ments in simple compounds . What Are the Trends in the Periodic Table ?

Examine the periodic table of the elements that your teacher provides Look in each square for the whole number located above the symbol ! the element . As you read across a row from left to right . what trend do you see ?

Now look at a column from top to bottom . What trend do you see in these numbers ?

Think It Over Interpreting Data Can you explain why one row ends and a new row starts ?

Why are certain elements the same column ?

How is the reactivity of elements related to valence electrons in atoms ?

what does the table tell you about the atoms ol elements ?

Key Terms valence electron I electron dot diagram chemical bond Why isnt the world made only of elements ?

How do the atoms of different combine to form compounds ?

The answers to these questions an lu their energy levels . And the roadmap to how electrons the properties is the periodic . Valence Electrons and Bonding You earlier about and levels . An utum valence are those electrons that have the highest energy level and are held most loosely . The number of valence electrons in an atom of an element determines many properties of that element . including the ways in which the atom an bond with other atoms . I Valencia Electrons Sky divers in the outer ring are less securely held to the group than are members of the inner 94 Similarly . valence electrons are more loosely held by an atom than are electrons of lower energy levels . 176

Electron Dot Each element has a number of valence electrons . ranging from I to . Figure shows one way to depict the number of valence in an element . An electron dot includes the symbol for the element surrounded by dots . Each dot stands for one valence electron . Chemical Bonds and Atoms of most elements are more is . less likely to they have eight valence electrons . For example , atoms of neon . argon . krypton . and xenon all have eight valence electrons and are very unreactive . These elements do not easily form pounds . Some small atoms . such as helium , are stable with just two valence electrons . Atoms usually react in a way that makes each atom more stable . One of two things can happen Either the number of valence electrons increases to eight ( or two , in the case of hydrogen ) Or . the atom gives up loosely held valence . that react this way can chemically . that is , to other atoms . A chemical bond is the force that holds two atoms together as a result of the re of electrons between them . Chemical Bonds and Chemical Reactions When atoms bond . electrons may be transferred from one atom to another . or they he shared between the atoms . In either case . the change results in a chemical is , new substances form . Later in this chapter . you will learn which elements are likely to gain electrons . which are likely to give up electrons . and which are likely to share electrons . You will also learn how the periodic table of the elements can help you predict how atoms of different elements react . being what does an electron dot Electron Dot Diagrams An valence electrons are shown as dots around the symbol of the element . Notice that oxygen atoms have six valence . Predicting How many more electrons are needed to make an oxygen atom stable ?

Home Period Table of the Elements The table of elements is arranged horizontally in order of increasing atomic number ( number at protons ) and vertically in columns of elements with similar chemical properties . Go For . Visit Web Code ! How the Periodic Table works The periodic table is a useful tool for identifying the elements in simple compounds . The table can also help you understand how atoms form bonds . The periodic table reveals the underlying atomic structure of atoms . including the ment of . If you know the number of valence that atoms of elements have , you have a clue as to which demerits combine and how . Periods and Groups look at Figure . Think about how the atoms change from left to right across a period . As the atomic number increases . the number of electrons also increases . Except for Period I , a given period ends when the number of valence electrons reaches eight . The next period begins with atoms having valence electrons with higher energy . This repeating pattern means that the elements within a group always have the some number of valence electrons . As a result . they have similar properties the electron clot diagrams of elements in Periods and . Notice that each element has one more valence electron than the element to its left . For example . Group I elements have one valence electron . The elements in Group have two . Elements in Group have three valence electrons . elements in Group have four . and so on . Elements in Groups to follow a slightly different pattern .

' LI Be Oi Ilium Nitrogen Oxygen Fluorine Neon no Na Al Sodium Magnesium Aluminum I Phosphorus Argon FIGURE I Patterns After the number of valence electrons reaches , a now begins Inert Gases Him ( Ix ( are thy at thew ' two . yuu , atoms with ' IlS not two . In the out ) Moms Arc or In . with other mull . do not with other elements so , to ) with other . Reactive and Metals Now look at the elements in the column iust to the left ot the gases . The in ( troop . have ( gait of lust mic thew the , number of tight in gases . result , the halogens react ily with other clam whose can up or share . the ' I , metals only one valence electron . for lithium . the new it . a of two ill the ' tan mun by their one valence electron . This property the i ( How an atom at tho elements in Group similar ?

Flaunt Reactivity of Chlorine so that steel wool bums when exposed to the gas ) jar . Relating ( ante and Effect Why if so ( 119 Tri other Metals ( at the in Groups through the periodic table . Like the Group I elements . these arc . one . two . or . They by losing thew ' they combine with oxygen or one of the . a is depends on how its lose valence electrons Sonic , such as those in Group ( the alkaline canh ) and arc almost as ' as alkali metals , lI ( in Group 10 and gold ( Au ) in Group are . In general , the reactivity of metals decreases from lull to right . Among Groups I and reactivity frum top In . Science and History 1894 Argon . Neon . Krypton . and Xenon British chemist William Ramsay discovered an element he named . after the Greek word for The name fits because argon does not react with other elements . Ramsay looked for other nonreactive gases and neon , and xenon . 1000

Other Elements in the green region of the periodic table are the . Five arr solids , four arc gases , and one is a liquid All of the als have four or more valence electrons . Like the halogens . other become stable when they gain or share to have of eight electrons . The combine with metals usually by gaining . But can also combine with other by forms of the periodic table sharing . Of the , oxygen and halogens exist . The periodic tables used are highly reactive . In fact . is the most reactive clement DY physicists and engineers known . It even forms compounds with some of the inert gases . may i , information than the tables used by chemists . Use the library to find two different forms of the periodic table . a paragraph comparing the two tables and how might use them 1997 Elements 101 to 109 The International Union of Pure and Applied agreed on names for elements to ! to . Marry ofthe names honor scientists is named after Glenn . is named after use , shown here In . All the new elements are synthetic and none stable enough In Although predicted the properties of an element he called . the element was not . chemist Marguerite Petey named her . liter the country France .

A It This watch keeps time with a small quartz crystal , a compound made of the silicon and the nonmetal oxygen The crystal vibrates at about vibrations per second when a voltage is applied Handing The quartz movement of the watch Several known as line between the metals and . The have from three to six . They can either lose or combine with other . So . on the conditions . elements can ) us either ur . Hydrogen Notice that hydrogen is located above Group I in the periodic table . II is it has only one valence electron . is not considered a . is reactive element . but its properties greatly those of the alkali metals Why is hydrogen grouped above the Group I ' elements even though it is not a metal ?

Reading Section Assessment Vocabulary Skill Academic Words Use the word to explain why the , tend ( easily with other . Reviewing Key Concepts . Defining What are valence electrons ?

huw Ihe is , is ( ef . Explaining Why do the properties of elements change i HINT . Reviewing What role do valence play in the ( from ?

Comparing and Contrasting Do oxygen atoms inure or less when forms ?

in regular tmy period ?

Relating Cause and Effect Explain the in terms . Activity for Elements Find some examples of elements at home . Then locate the elements on the periodic table . Show your examples and the periodic table to your family , Point out the positions at the elements on the table and explain what the periodic table tells you about the elements . Include at least two your ! Ol . Hint The nonmetal may be invisible .

um Comparing Atom Sizes Problem How is the radius of an atom related to its atomic number ?

Skills Focus making models , graphing . interpreting data Materials drawing compass metric ruler calculator periodic table of the elements Procedure . Using the periodic table as a reference , whether the size ( radius ) of atoms will increase , remain the same , or decrease as you go from the top to the bottom of a group , or family , of elements . The data table lists the elements in Group in the periodic table . The atomic radius of each element is given in ( Copy the data table into your . Use the periodic table to look up the atomic numbers of the Group elements . Record the values in your data table . Calculate the relative radius of each atom compared to beryllium , the smallest atom listed . Do this by dividing each radius by the radius of beryllium . Hint The relative radius of magnesium would be 160 divided by 112 , or . Record these values , rounded to the nearest tenth , in your data table . Using a compass , draw a circle for each element with a radius that corresponds to the relative radius you calculated in Step . Use centimeters as your unit for the radius of each circle . CAUTION Do not push the sharp point of the compass against your skin . Label each model with the symbol of the element it represents . Data Table em a ' Ba i ' Me . Err 215 222 A ( pin ) is on of . Analyze and Conclude . Melting Models Based on your models . was your prediction in Step correct ?

Explain . Graphing Make a graph of the data in the second and third columns of the data table . Label the horizontal axis Atomic Number . Mark the divisions from to 60 . Then label the vertical Radius and mark its divisions from to 300 . Interpreting Data What trend does the graph show ?

Is the relationship between the linear or nonlinear ?

Predicting Predict where you would the largest atom in any group , or family , of elements What evidence would you need to tell if your prediction is correct ?

Communicating Write a paragraph explain ing why it is useful to draw a to two centimeter model of an atom that has an actual radius of to 200 . More to Explore Look up the atomic masses for the Group elements . Devise a plan to model their relative atomic masses using objects chapters

00 Students know that are formed by combining two or more different elements and that compounds have proper ties that are ( their constituent elements Students atoms and molecules solids by ing up repeating patterns . such as the crystal structure ol Na ( or polymers How do ions form bonds ?

How are the formulas and names at ionic compounds written ! What are the properties of ionic compounds ?

Key Terms ion polyatomic ion I ionic bond I ionic compound I chemical formula subscript ' crystal Ci It you transfer a to your friend . both of you will have the money you need . 1840 Ionic Bonds . Standards How Do Ions Form ?

Place three pairs ol checkers ( three red and three black ) on your desk . The red represent electrons and the black represent protons . Place nine pairs of checkers ( nine red and nine black ) in a separate group on your desk . Move a red checker from the smaller group to the larger group . Count the number of positive charges ( protons ) and negative charges ( electrons ) in each group . Now sort the checkers into a group of four pairs and a group of eight pairs . Repeat Steps and , this time moving two red checkers from the smaller group to the larger group . Think Over what was the total charge on each group before you moved the red checkers ( electrons ) What was the charge on each group alter you moved the checkers ?

Based on this activity , what do you think happens to the charge on an atom when it loses electrons ?

when it gains electrons ?

You and at friend walk past a that apples for 40 catch and penis for 50 each . You 45 and want an our also has 45 cents but . You that if you give your friend a nickel , she will have cents and can buy pear . You will have 40 cents left to buy an . tho gets both of you what you . Your ' model . in at way . what can happen atoms .

atoms talking together rri about to electron ! IONS with , six . or seven valence electrons usually become more stable when this number increases to eight . Likewise , most alums with one , two , or three valence can lose electrons and become more stable . When these two types of atoms combine , or bond , electrons arc from one type of atom to the other . The transfer makes both types of atoms more stable . How Ions Form An ion ahn ) is an atom or group of atoms that has an electric charge . When an atom loses an electron . it loses a negative charge and positive ion . When an atom gains an ( it gains negative charge and becomes negative ion . Figure lists some ions you will often see in this book . Use this table as a reference while you read this section and other chapters . Polyatomic Ions Notice in Figure that some ions arc made of several atoms . For example , the ammonium ion is made of nitrogen and hydrogen atoms . Ions that are made of more than one atom am called ( er uh ) so means atoms . You can think of at polyatomic ion as group of atoms that reacts as a unit . Like other ions . polyatomic ions have an positive or negative charge . Now does an ion with a charge of form ?

I Ions are atoms that have lost or gained electrons . Interpreting Tables How many electrons does a sulfur atom gain when it a ion ?

How Ions Form When an atom loses one of its electrons . it a positively charged ion . The atom that gains the becomes a negatively charged ion . Ions and Their Charges Home Drugs ' Formula lithium Li Sodium Na Potassium Ammonium Calcium i Ca Magnesium Aluminum AP Fluoride Chloride Iodide Bicarbonate NCO , mime No , Oxide Sulfide Iv Carbonate CO , Phosphate .

03 ?

Bonds Look at Figure to see how sodium atoms and chlorine atoms combine to sodium chloride ( table salt ) Notice that sodium has one valence electron and chlorine has seven valence electrons . When sodium valence electron is transferred to chlorine , both atoms become ions . The sodium Formation of an atom at positive ion ( Nai ) The chlorine atom Bond a negative ion ( CI ' min , Om between Because oppositely charged particles attract . the positive metals in Group I and in Group 17 . Follow the process below to see how an ionic bond forms between a sodium atom and a chlorine atom . Cause and Effect Why is Na ion and the negative ion attract each other . An is the attraction between two oppositely charged positive and negative ions . A compound that consists of live and negative ions . such as sodium chloride . is called an sodium chloride electrically neutral ?

ionic compound . III Soil ! Atom Chlorine Morn A sodium atom has A chlorine atom one valance . move when the electron stable Mien it is ion the atom gains one electron . becomes more stable of an electron ion with a 10 charge . ion with a . A sodium metal A gas Sodium Ian Chloride Ion The sodium atom . The chlorine becomes a sodium a becomes a chloride Compound Sodium The positive sodium Ions and negative chloride ions each other . This attractive force is an ionic bond . Each sodium ion balances the charge oi one chloride ion so overall , the compound is electrically neutral

Chemical Formulas and Names Compounds can be by chemical formulas . A chemical formula is it combination of symbols that shows the ratio in a compound , For example . the formula for magnesium chloride is ( il . What does the formula tell you ?

of Ionic Compounds from Figure you know that the charge on the ion is . When ionic compounds form , the ions come together in a way that out the charges on the ions . The chemical formula for the compound this balance . Two chloride ions , each with a charge of will balance the charge on the ion . That why the of magnesium chloride is . The number is a subscript . subscript tells you the ratio of elements in the compound . For . the ratio of ions to chloride ions is I to . If no subscript is written . the number is understood . For example . the formula tells you that there isa I to ratio of sodium ions to chloride ions . lor compounds atomic ions are written in it similar way . For example . calcium carbonate has the formula ( Naming Ionic Compounds Magnesium chloride . sodium , sodium do these come from ?

For an ionic compound , the name of the positive ion comes first , followed by the name of the negative ion . The name of the positive ion is usually the name metal . But . at few positive ions exist . such as the ammonium ion ( if the ion is a single element . as already wen with sodium chloride , the end ofits name changes to . For example , is limited magnesium oxide . If the negative ion is , its name usually ends in or . as in Figure . The compound , named ammonium nitrate . is a common for gardens and ( Top plants . Joann What is the name of the ionic compound with the ) Flaunt 10 Calcium Carbonate . Interpreting Data Use the periodic table and Figure to Identify the charges of the ions in each ionic compound listed below . Then write the formula for each compound , sodium bromide lithium oxide magnesium sulfide aluminum fluoride potassium nitrate ammonium chloride How did you know how many of each ion to write in the formula ?

The white cliffs ol Dover , England . are ( i made of chalk formed lrom the remains it of tiny sea organisms , Chalk is mostly an ionic compound , calcium carbonate .

mam Crystal Clear Can you grow a salt crystal ?

Add table salt to a jar containing about 200 of hot tap water and stir . Keep adding salt until no more dissolves and it settles out when you stop stirring . Tie a large crystal of coarse salt into the middle of a piece of thread . Tie one end of the thread to the middle of a pencil . Suspend the other end of the thread In the solution by laying the pencil across the mouth of the yar . Do not allow the crystal to touch the solution . Place the jar in a quiet , undisturbed area . Check the size of the crystal over the next few days . Observing Does the salt crystal change size over time ?

What is its shape ?

What do you think is happening to the ions in the solution ?

Haunt It ionic Crystals The ions in ionic compounds are arranged in specific dimensional shapes called crystals . Some crystals have a cube shape like these crystals of halite or sodium chloride . Mating What holds the ions together in the crystal ?

ill Properties of Ionic Compounds Compounds have properties that are from their . You have already read about the properties of metals and . But what about the properties of ionic compounds formed when metals and react ?

In general . ionic compounds are hard . brittle solids with high melting points . When melted or dissolved in water . they conduct electric current . Ionic Crystals Ionic compounds form solids lay building up repeating patterns of ions . Figure I shows a chunk of a halite . or rock salt . which is how sodium chloride occurs naturally . Pieces of halite have sharp edges . corners , surfaces , and cubic shape . Equal numbers of Na and ions in solid sodium are attracted in an alternating , as shown in the diagram . The ions form an . called a crystal . In an ionic compound , ion is attracted to ions of opposite charge that surround it . The pattern formed by the ions remains the same no matter what the sir crystal . in a single grain . the crystal pattern extends for millions of ions in every direction . Many crystals of ionic compounds are hard and brittle . due to the strength of their ionic bonds and the attractions among all inns . High Melting Points When you a substance such as table salt , its energy increases . When the ions have enough energy to overcome the attractive forces between them . they away from each other . The ionic crystal melts into a uid . Because ionic bonds are strong , a lot is in break them . As a result , ionic compounds have high inciting points . For example . the melting point of table salt is .

Freon 12 Ions in Solution A solution of sodium chloride conducts electric current across the gap between the two black rods of a conductivity tester . As a result . the bulb up . current is the of changed particles . When ionic crystals dissolve in water . the bonds ions are broken . As a result . ions are free to mow about , and the solution conducts current . Likewise , after an ionic compound melts , the ions are able to mow freely , and the liquid conducts current . In contrast . ionic compounds in solid form do not conduct current well . The ions in the solid crystal are tightly bound to other and can not from place to place . if charged particles can not move . there is no current . What is a crystal ?

Section For Links an ionic compounds Visit Web Code . Target Reading Skill Compare and Contrast ( your comparing the of sodium . chlorine . and sodium chloride . Expand the table by adding columns for melting point and conductivity . Then compare these properties . Reviewing Key Concept . I . Reviewing What is anion ?

Comparing and Contrasting Contrast sodium and ions , including how they form . Write the symbol for each ion . Relating cause and Effect holds together in sodium chloride ?

Indicate the charges that are involved . Identifying What is given by the formula of an ionic compound ?

Explaining The formula for sodium is . Explain what this formula means . 999 Applying Concepts Write the formula for calcium chloride . Explain how you determined this formula . I . Listing List three properties of ionic compounds . Making Relate each property that you listed to the of ionic bonds . Writing Ill Science ' the of an atom . and you are observing a reunion batman I atom and a fluorine atom . Write an account of the ofan asthe atoms react . Tell what happens to the valence electrons on ad atom and how cacti is by losing or gaining electrons . chapters in

Distilled water Shedding Light on Ions Sodium chloride chloride Problem what kinds oi compounds produce ions in solution ?

Procedure a . Make a conductivity tester as described sums below or , if you are using a conductivity controlling variables , interpreting data , inferring probe . see your teacher for instructions . Then make a data table in your notebook similar to the one above . dry cells , Pour about 50 of tap water into a small small light bulb and socket or beaker . Place the copper strips in the beaker . gang , of , conductivity Be sure the strips are not touching each , dips on be , end , Nob . other . Attach the alligator clip of the free . end of one wire to a copper strip . Do the wan same with the other wire and the other . make , per strip . Record your ' Wall . Disconnect the wires from the copper ' Sodium chloride lake the strips out of the beaker . and pour graduated cylinder . out the tap water . Dry the inside of the sucrose ker and the copper strips with a paper towel . by each . Four 50 of distilled water into the beaker . Reconnect the conductivity tester and test the water as in Step . Keep the copper strips about the same distance apart as in Step . Record your observations . Making a Conductivity A . Use wire with alligator clips to connect the positive terminal of a dry cell to a lamp socket . CAUTION The bulb is fragile and can break . I . Similarly connect another wire between the tive terminal ot the cell and the positive terminal of the second cell . Connect one end of a third wire to the negative terminal of the second dry cell . Connect one end of a fourth wire to the other terminal of the lamp .

. Use or sodium chloride to make a small pile on a clean piece of paper . Dry off the copper strips of the conductivity tester and use it to test the conductivity of the sodium chloride . Record your observations . Add spoonful of sodium chloride to the tilled water in the beaker . Stir with the spoon until the salt dissolves . Repeat the ity test and record your observations . Disconnect the conductivity tester and rinse the beaker , spoon , and copper strips with tilled water . Dry the beaker as in Step . Test sucrose ( table sugar ) in the same ways that you tested sodium chloride in Steps through . Test additional materials supplied by your teacher . I It the material is a solid , mix spoonful ot it with about 50 of distilled water and stir until the material dis solves . Test the resulting mixture . If the substance is a liquid , simply pour about 50 into the beaker . Test it as you did the other mixtures . Analyze and conclude . Designing Experiments What were the able parameters in your experiment ?

What were the controlled parameters ?

Controlling Variables why did you test both tap water and distilled water before testing the sodium chloride solution ?

Could you have used tap water in your tests instead of distilled water ?

Explain . Drawing Conclusions Based on your , add a column to your data table indicating whether each substance ions in solution . Inferring How can you account for any observed differences in conductivity between dry and dissolved sodium chloride ?

Communicating Based on your observations , decide whether or not you think sucrose is made up of ions . Explain your answer . Design an Experiment Design an experiment to test the effects or ing the spacing between the copper strips of the conductivity tester . Obtain your teachers sion before carrying out your investigation .

Standards Focus ( All Students know that pounds are formed by combining two or more elements and that ( have proper ties that are from their elements Students know can be classified by their properties , their melting lure , density , hardness . and thermal and . what holds bonded atoms together ?

What are the properties of ( How does unequal sharing ol ?

Key terms I bond I I double hand I triple bond compound I polar bond I bond 13 Sharing One student is a skilled artist . Covalent Bonds , Standards Can Water and Oil Mix ?

Four water into a small jar that has a lid until the jar is about a third full . Add an equal amount of vegetable oil to the jar . Cover the jar tightly . Shake the jar vigorously for 20 seconds . Observe the contents . Allow the jar to sit undisturbed for minute . Observe again . Remove the top and add drops of liquid detergent . Cover the jar and repeat Steps and . Think It Over Forming Operational Definitions Based on your observations , write an operational definition of detergent How might your observations relate to bonds in the detergent , oil , and water molecules ?

Uh uh , you ' a big due in ni You need to in story and illustrate it with . Art ) been your best . but writing takes more effort . luckily . you working with a partner who writes well but doc in art . you each contribute your skills , you can at . while the other is a skilled writer . By pooling their skills , the students ( an complete their . 191

How Covalent Bonds Form lust as you and your friend can work together by sharing your talents , atoms can become more stable by sharing elections . The chemical bond formed when two atoms share electrons is called a covalent bond . Covalent bonds usually between atoms of . In contrast , ionic bonds usually form when a metal combines with It nonmetal . Electron Sharing can bond to other by sharing electrons . So can hydrogen . Most can even bond with another atom of the same element Figure illustrates how two atoms can react by sharing a pair of electrons . By sharing electrons , each atom has a ble set of eight . The force that holds atoms together in a covalent bond is the attraction of each atom nucleus for the shared pair of electrons . The two bonded atoms form a molecule . A molecule is a neutral group of atoms joined by covalent bonds . Bonds ?

Look at the electron dot diagrams in Figure . Count the valence electrons around each atom that reacts . Hydrogen has one valence electron . Oxygen has six . Nitrogen has five . The number of covalent bonds that a metal atom can form equals the number needed to make a total of eight . For example , oxygen has six valence , so it can form two covalent bonds . In a water molecule . oxygen one covalent bond with each of two hydrogen atoms . As a result , the oxygen atom has a stable set of eight valence electrons . hydrogen atom can form one bond because it needs only a total of two electrons to be stable . Oxygen Hydrogen atom atom mom I I I a nitrogen atom I A water molecule Art ammonia molecule I has three covalent booth bonds . FIGURE 15 Sharing Electrons By sharing electrons in a covalent bond . each fluorine atom has a stable set of eight valence electrons . Fluorine smug Frame 15 Covalent Bonds The oxygen atom in water and the nitrogen atom in ammonia each have eight valence electrons as a result of forming covalent bonds hydrogen atoms . Interpreting Diagrams How many covalent bonds can a nitrogen atom form ?

nouns 9193 An oxygen has one double bond . Nitrogen atom A nitrogen molecule has on band . A carbon dioxide molecule has two bond Flaunt Double and Triple Bonds Double and triple bonds can form when atoms share more than one pair of electrons . Diagrams In a nitrogen molecule , how many electrons does each nitrogen atom share with the other ?

91121119 For Links on Visit Web ( ode ! Bonds and Triple Bonds Look at diagram of the oxygen molecule ( 03 ) in Figure . What do you see different ?

This time the two atoms share two pairs of , forming a double band . In a carbon dioxide molecule ( carbon a double bond with each of two oxygen atoms , Elements such as nitrogen and carbon can form triple bond in which atoms share three pairs . What is tho between a double bond and ! bond ?

Molecular Compounds A compound is a compound that is composed of molecules . The molecules of a molecular compound contain atoms that are bonded . Compared to ionic pounds , molecular compounds generally have lower melting points and boiling points . And . ionic compounds . molecular compounds do not conduct electric current when melted or dissolved in water . Low Melting Point and Boiling Points Study the table in the Analyzing Data box on the next page . lists the melting points and boiling points for a low molecular compounds and ionic compounds . molecular solids . forces hold the close to one another . But , the forces between molecules are much weaker than the forces between ions in an ionic solid . Compared with ionic solids , less heat must be added to solids to separate the molecules and change the solid to a liquid . That is why most familiar compounds that are liquids or gases at room temperature are molecular compounds .

Moth Statistics . Data Analysis . and Probability . II III II Melting Points and Boiling Points of Comparing Molecular and Molecular and Ionic Compounds Ionic Compounds The table compares the melting points and Substance Formula ?

boiling points of a tew molecular compounds and ionic compounds . Use the table to answer the following questions . Graphing Create a bar graph of just the melting points of these compounds . Arrange the bars in order of increasing melting point . The should start at and go to 900 . Interpreting Data Describe what your graph reveals about the melting points of molecular compounds compared to those of ionic compounds . Inferring How can you account for the in melting points between molecular compounds and ionic compounds ?

Interpreting Data How do the boiling points of the molecular and ionic compounds compare ?

Molecular compound Ionic compound . Predicting Ammonia melting point is ( and its boiling point is . ammonia a molecular compound or an ionic compound ?

Explain . Poor Conductivity Most molecular compounds do not conduct . No charged are available to move . so there is no current . Materials such as plastic and ber are used to insulate wires because these materials are posed of . Even as liquids , compounds are poor conductors . Pure water . for example . does not conduct electric current . Neither does table sugar or alcohol when they are dissolved in pure water . Unequal Sharing of Electrons Have you played tug of war ?

If you have . you know that if both pull with equal fora . the contest is a tie . But what if the teams pull with unequal forces ?

Then the rope moves toward the side of the stronger team . The same is true of in a covalent bond . Atoms of some elements pull more strongly on shared than do atoms of other . As a result , the electrons are shared unequally . Unequal sharing of electrons causes the bonded atoms to have slight electrical charges . om

From Nonpolar and Polar lands Fluorine a nonpolar bond with another atom . In hydrogen . attracts electrons more strongly than hydrogen does . so the bond formed is polar . Fluorine molecule Equal pull hydrogen fluoride molecule ) Unequal pull Flaunt 18 Nonpolar and Polar Molecules A carbon molecule is a nonpolar molecule because of its shape . In contrast , a water molecule is a polar molecule because of its bent shape . Interpreting Diagrams What do the arrows in the diagram show ?

Polar Bonds and Nonpolar Bonds The unequal sharing of electrons is enough to make the atom with the stronger pull slightly negative and the atom with the weaker pull slightly positive . A covalent bond in which electrons are shared unequally is called a polar bond . Of course . if two atoms pull equally on the electrons . neither atom becomes charged . A covalent hood in which electrons are shared equally is a bond . Compare the bond in ( with the bond in hydrogen ( in Figure . Polar Bonds In Molecules A molecule is considered polar if it has a positively charged end opposite a negatively charged end . For example , hydrogen is a polar molecule . ever , not all molecules containing polar bomb are polar . For example , in carbon dioxide . the oxygen atoms attract electrons much more strongly than carbon does . So . the bonds between the oxygen and carbon atoms are polar . But . as you can see in Figure a carbon dioxide molecule has a shape . As a result . the two oxygen atoms pull with equal strength in opposite directions . The attractions cancel out . making the molecule nonpolar . In contrast . a water molecule . with its two polar bonds , is itself polar . A water molecule has two hydrogen atoms at one end and an oxygen atom at the other end . The oxygen atom attracts electrons more strongly than do the hydrogen atoms . As a result . the oxygen end has a slight negative charge and the hydrogen and has a slight positive charge . Attractions Among Molecules It you could shrink small enough to move among bunch of water molecules , what would you find ?

The negatively charged oxygen ends of the polar water molecules attract the positively charged hydrogen ends of nearby water molecules . These attractions pull water molecules toward each other . In contrast , there is little attraction among . nonpolar molecules . such as carbon dioxide molecules . Nonpolar Molecule Polar Molecule Carbon dioxide water ( av ) Opposite pulling cancels toward oxygen

Target Reading Skill compare and contrast Reviewing Key Concepts The properties of polar and nonpolar compounds because ol in their molecules . For , water and vegetable oil do mix . The molecules in vegetable oil are Iar . and molecules have attraction for polar waiter ( On the other hand . the waiter arc more strongly to om another than to the molecules of oil . Thus . stays with oil stays with oil . If you did the Standards activity , you found that adding oil and water to mix . This is because one end of a molecule has nonpolar covalent bonds . The other end includes an ionic bond . The end mixes easily with tho oil . the ionic end is attracted to polar waiter . so dissolves in water . Reading Why is water ( a polar molecule but a 9209553 ) Is not ?

Assessment Section ( a table comparing the properties of molecular and ionic ( Identifying is that holds I two bonded atoms together ?

Inferring A carbon atom can form tour covalent . How many valence electrons it have ?

Interpreting Diagrams What is double bond ?

Use Figure 16 to explain how carbon dioxide has it stable all eight valence electrons for each atom . Reviewing How are the properties of molecular different front those ol ionic compounds ?

Relating Cause and Effect Why are most compounds poor conductors ?

Reviewing How do mine atoms in covalent bonds become slightly negative or slightly positive ?

What type bonds do them atoms ?

19 Out the bin Most laundry dirt is oily or greasy . Detergents can mix with both oil and water , so when the wash water goes down the drain , the soap and dirt go with it . 04711 Reading moi . Comparing and Contrasting Both carbon dioxide molecules and water have polar . Why then is carbon a nonpolar molecule while water is a polar ?

Predicting Predict whether carbon dioxide or would have a higher . your prediction in terms of the attractions . Laundry Chemistry Demonstrate the action of soaps and detergents to your family Pour some vegetable oil on a clean cloth and show how a detergent solution can wash the oil away better than water alone ( an . Explain to your family the of soap and detergent molecules in terms of their chemical bonds . 197

, 39 00 Section Students know can by their including their melting tempera lure , density . hardness , and thermal and . How do the properties of metals and alloys How do metal atoms combine ?

How does metallic bonding result In useful properties 01 metals ?

Key Terms I alloy I ( bond FIGURE 20 Metal In The Guggenheim Museum in , Spain . makes dramatic use of some properties of metals . The museum shiny outer skin is made of the lightweight metal titanium . which can be pressed into large . thin , flexible sheets . Ted ! Design Bonding in Metals Are They Steel the Same ?

Wrap a stainless steel bolt . wire nail ( steel ) and a cut nail ( carbon steel ) together in a paper towel . Place the towel in a bag . Add about 250 of saltwater and seal the bag . After one or two days , remove the nails and bolt . Note any changes in the metals . Think It Over Developing Hypotheses What happened to the three types of steel ?

which one changed the most , and which one changed the least ?

What do you think accounts for the difference ' would you choose metal to ( user the ' of this building in Figure 20 ?

You could cover the building with . crumbly such as sulfur or silicon . What pi ( i li wire . pom and pans . ils , and strong for buildings ?

do have these physical properties ?

Metals and Alloys You a piece of metal when you see it . it usually hard . dense . and shiny . At room temperature , most metals are solids . They can be hammered or drawn out into thin wire . Electronics such as stereos . computers . and players have metal parts because metals conduct electric current . Yet , very few of the metals you use every day consist of just one element . Instead . most of the metallic objects you see and use are made of alloys . An alloy is a mixture made of two or more elements , at least one of which is at metaL Alloys are ally stronger and less reactive than the pure metals from which they are made . Physical Properties The properties of an alloy can differ greatly from those of its elements . But depending on how they are mixed . alloys also retain many of the physical properties of metals . For example . pure gold is shiny . but it is soft and easily bent . For that reason , gold jewelry and coins are made of an alloy of gold mixed with a harder element . such as copper or silver . These gold alloys are much harder than pure gold but still retain their beauty and shine . Even after sands of years . objects made of gold alloys still look exactly the same as when they were first made . Chemical Properties iron is strong metal that you might think would be good for making tools . However . iron objects rust when they are exposed to air and water . For this reason , iron is often alloyed with one or more other elements to make steel . Tools made of steel are much stronger than iron and resist rust much better . For example . forks and spoons made of stainless steel am be washed over and over again without rusting . because stainless alloy of iron . carbon . nickel , and not react with air and water as iron dues . Why is most jewelry made of gold alloys rattler than pure gold ! HEURE 21 Bass Trumpet Brass is an alloy of the elements copper and zinc . What are some metallic properties of brass that you ( an see here ?

Flaunt 22 Gold and Steel This pipe is made at steel . The necklace is made of gold alloys .

73 , Try rum Activity What Do Metals Do ?

Your teacher will give you pieces ol different metals . Examine each metal and try changing its shape by bending , stretching , folding . or any other action you can think of . Write down the properties that are common to these metals . Write down the properties that are different . What properties make each metal suitable for its intended use ?

Inferring What properties must aluminum have in order to be made into toil ?

Flaunt 23 Metallic Bonding The type of bonding in metals is the result of loosely held electrons . Problem Solving Why would nonmetal be unlikely to have the type of bonding shown here ?

Solid metals consist at positively charged ions surrounded by a loose sea at valence electrons Metallic Bonding The properties of solid metals and their alloys can be explained by the of metal atoms and the bonding between those atoms . Recall that most metals have I . or valence electrons . atoms chemically with atoms of other . they usually low valence electrons . charged metal ions . easily because their are not strongly held . Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom . Mast arc crystalline solids . Within each crystal . the metal atoms as . packed . positively ions , The valence electrons drift among the ions . Each metal ion is held in by metallic attraction a positive ion and the many electrons surrounding it . Figure 23 illustrates the metallic bonds that hold together foil . Th positively charged metal arc in El scan of valence electrons . The more valence electrons an atom can add to the the metallic bonds will . What a metallic bond )

Metallic Properties Suppose that you placed one hand on an unheated aluminum pan and the other hand on a wooden tabletop . The aluminum pan would feel cooler than the tabletop even though both are at the same temperature . You feel the difference because num conducts heat away from your hand much faster than wood does . Metal called 21 heat sink are used inside many electronics to cool their insides . However . a metal ability to conduct heat is even more useful if the metal can be bent or hammered into a useful shape . OThe sea of electrons model of metallic bonding helps explain the malleability . ductility . luster . high electrical conductivity , and high thermal conductivity of solid metals . Each of these is related to the behavior of valence electrons in metal atoms . and Most metals are and can he reshaped easily . They can be stretched . pushed . or pressed into different shapes without breaking . Metals act this way because the positive ions are attracted to the loose all around them rather than to other metal ions . These ions can be made to change position , as shown in Figure 24 . However . the metallic bonds between the ion and the rounding keep the metal from breaking . Because the metal ions move easily , metals are ductile , which means that they can be bent easily and pulled into thin strands or wires . Metals are to be rolled into thin sheets . as in aluminum foil . or beaten into complex shapes . of art . For links on homing Welt ( ode ! 24 of Mauls Most metals can be reshaped be ( ause their ions can be pushed easily out at position . metal Ions an be . made to change position . cap , on metals can be and Metal ions shift .

noun 25 Luster and Conductivity of Metals The unique properties at metals result from the ability or their electrons to move about freely . 2020 Luster Gold in an astronauts ( ace shield reflects sunlight , protecting the wearer eyes . Electrical Conductivity Metal strips on a board conduct electric current throughout the . Luster Polished metals have high is . they are shiny and . A luster is due to its . When light strikes . they absorb the light and then it nil again , This property useful for products as varied its mirrors . buildings . and helmets . Electrical Conductivity You may recall that when charged particles are free in move an electric current is . Metals conduct easily because the electrons in a metal can move freely among the atoms . When connected to device such as it battery . electric current into the metal at one point and out at another point . Thermal Conductivity Recall that energy from warmer matter to cooler matter . When this happens , the greater motion til the particles in the parts of the rial is along to the particles in the cooler parts . This of thermal energy is known as heat . Metals conduct easily because of the ' electrons freedom of motion within metal or metal alloy . why do metals conduct electric current

Section Assessment Conductivity Metal cool a motorcycle engine by conducting heat to the skill Words Us the word in that one uf ) Reviewing Key Concepts mu is an ?

Reviewing From metals is mu ?

I eel made I . Comparing and Contrasting ( and contrast and . is bond ?

Relating Cause and Effect huw ' iL , do the play ?

Comparing and Contrasting you learned earlier hands . How dim a ) limit ! differ an . bond ?

Reading . Writing . A . Listing Name metals . accounts In light . tungsten ' win is in at mil ( Describe two properties til the malt it good ' for . Applying it , to us MINT mixing spoon cooking , on stove ?

Wri ing in Science Product Choose a familiar metal object and create ii product label for It . Your label should describe at least two of the metal and explain why it exhibits those properties . You should include illustrations on your label as well . 203

Chapter Study Guide Alums oi elements compounds by gaining . losing , or sharing . Kto , a ' a Periodic Table Key Concepts Th , in an alum element uf , in which the atom hand mun . The periodic table the ul alums . of the . Key Terms dol bond ' Ionic Bonds Key Concepts , the ' and ions . When . form . the ( on . For compound , the name of the um . name ' mu . In , compound , luv high Inching and conduct when in water . Covalent 30335 Key ( Tho that holds hand is the fun the shared pair uf . Molecular ( Imp ( points and du . I ul mum In have . Key Terms bond bond triple bond ' Bonding in Metals Key a I . arc and ' hay arc nude . alums in , in . arr In ( atom to Atom . In . mud In . Key Terms Key Terms ) 10 ( compound 2040

Review and Assessment . um for Visit Web Code ( Target Reading me , How am , Compare and Contrast ( Chemical Bond Bonded Atoms ' on ionic band a . Wes , positive and . Polar bond . of electrons i Nonpolar bond . molecule ?

yes positive Reviewing Key Terms Choose the letter oi the best answer . HINT I held most loosely . of lowest energy level , lost . dot show an ' proton . valence electrons . bonds . When an alum Imus or gain . il ( iii ion . crystal . subscript . A in which are is a . polar bond . bond . The alarm in stainless arc together by ionic . polar bomb . bands . I . in morn arc those that art Complete the following so that your answers clearly explain the key terms . When atoms read , they form A chemical min hand . lIl ( is . ions su ( as ammonium ions nu I , consist ul . anionic MINT ! means ( The formulas , and all represent ! molecules . which arc . 10 . Pure tend to be weaker and more than an , which is a . Wri ing in Science comparing and contrasting Go to your local grocery store and observe how the products on the shelves are organized . Write a paragraph comparing how foods are organized in a grocery store and how elements are organized In the periodic table . Atom and Handing ,

Review and Assessment Checking Concepts 11 . Which element is less . an element atom hat seven ' an whim atom ' I ' right valence ?

12 . tonic compounds ' high ?

13 . The acid li . How many ' in um acid ?

14 . How is at an ionic bond 15 . Why is bond two ul same a ?

how metallic causes metals to , 17 . Generalizations does the of the tell you ' an may lie ?

18 . Classifying Classify below as either polar or . your reasoning . Oxygen Carbon dioxide 19 . Relating Cause and Effect . mall ' arc mum . Water . is at liquid . Use yuu polar ' to explain this . Hint til gas are much apart than of a 20 . Applying Concepts Why docs horseshoe bend but not break when a ' 206 Skills Use the electron dot diagrams below to answer Questions as Hydrogen Argon Sud ! um . Nitrogen Oxygen 21 . Predicting When and , what will the of tu in mul uf the resulting ?

can stable by losing um ?

Explain . 23 . Drawing Conclusions which of these is least tu react with ?

interpreting Diagrams Which at these would ( with two ( tu form an ionic ?

Explain . 25 . Classifying What hunt when rim atoms or nitrogen join to form a nitrogen ?

When join in an ?

Standards Investigation Performance Assessment yuur ' In class , telling what the parts . why you ' In the and . kind of bonds were ?

more would you like to ) that could ?

Standards Practice Choose the letter of the best answer . What is the atomic number of calcium ?

A I 20 ( 48 Use the electron dot diagrams below to answer Questions . Which element is the most likely to lose two electrons and form an ion with a charge of ?

A potassium ( oxygen ( magnesium ( aluminum ( Al ) Oxygen has valence electrons . as indicated by the ( dots the letter symbol . Based on this , how many covalent bonds could an oxygen atom form ?

A six three two none . If a reaction occurs between potassium ( and oxygen . what will he the ratio of potassium to oxide ions in the resulting compound . potassium oxide ?

A I . The element boron ( is directly above aluminum ( Al ) on the periodic table . Which statement about boron is true ! A Boron is in the same period as aluminum and has two valence electrons . Boron is in the ram group as aluminum and has two valence electrons . Boron is in the same period as aluminum and has three valence electrons . Boron is in the same group as aluminum and has three valence electrons . An cube solid ) and a scoop of table salt ( are left outside on a warm . sunny day . Which best explains why the ice cube melts and the salt does not ?

A The attractive forces between molecules of are much weaker than those between ions in . I can dissolve in . The mass of the was less than the mass ofthe . is white and is colorless . The diagram below shows the crystal structure at sodium chloride . Use the diagram to answer Question . In crystal of sodium chloride . each sodium ion is attracted to the A other sodium ions surrounding it . I chloride ions surrounding it . neutral sodium atoms surrounding it . neutral chlorine atom surrounding it . ic table to the ' of I . Use the period valence electrons for potassium ( calcium ) aluminum ( Al ) oxygen ( and iodine ) Then write the formulas for the potassium iodide . calcium oxide . aluminum iodide . and potassium oxide . 0307