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ACTIVE LEARNING IN CHEMISTRY EDUCATION

"ALICE"

CHAPTER 11

PERIODICCLASSIFICATION

OF THEELEMENTS

The Periodic TableFamilies of Elements

11-1 ©1997, A.J. Girondi

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© 1997 A.J. Girondi, Ph.D.505 Latshmere DriveHarrisburg, PA 17109

alicechem@geocities.com

Website: www.geocities.com/Athens/Oracle/2041

11-2 ©1997, A.J. Girondi

SECTION 11.1 Introduction to the Periodic Table

So far in your study of chemistry, you have spent most of your time learning about the physicalprinciples which determine the behavior of atoms and molecules. These principles allow us to predict howtemperature, volume, and pressure changes affect gases. They also allow us to solve mass-mass andmass-volume problems using balanced chemical equations. We have also been able to use physicalprinciples to determine atomic masses and chemical formulas using experimental data. However, they donot tell us much about the actual physical and chemical properties of specific chemical substances.

A working knowledge of chemistry should include familiarity with the actual properties of chemicalsubstances, as well as an understanding of the laws that govern chemistry. Hopefully, you will begin todevelop this working knowledge as you study this chapter. Each element has its own characteristic set ofproperties that help to distinguish it from other elements. As early as the 1800's, chemists began to lookfor similarities among elements that would allow them to be classified into groups. Early chemists knewthat it would be much easier to study groups of elements rather than each of the elements individually.

The task at hand was to develop a way of arranging the elements so they could be groupedaccording to common traits. The Russian chemist Dmitri Mendeleev was the first person to successfullyarrange the elements in an orderly fashion. He arranged the elements in order of increasing atomicmasses in 1869. He then developed a table in which elements with similar chemical properties wereplaced in the same vertical columns. This table was later called the "Periodic Table of the Elements."

Mendeleev received a considerable amount of ridicule for his arrangement. His colleaguesjokingly suggested that he try arranging the elements alphabetically! Mendeleev ignored the ridicule andremained committed to his method of arrangement. In the preparation of his table, if the element with thenext highest atomic mass did not fit a particular group, Mendeleev left a blank space on his table andmoved the element up to the next higher group. This resulted in several blank spaces in his table ofelements. He believed that these blank spaces would eventually contain elements that had not beendiscovered yet. He predicted the properties of three of these unknown elements. All three werediscovered in Mendeleev's lifetime and were found to have properties very close to what he hadpredicted! This proved that Mendeleev's arrangement of elements was, indeed, useful.

From his studies, Mendeleev concluded that both the chemical and physical properties of theelements vary in a periodic (repeating) fashion with increasing atomic mass. The horizontal rows in thetable are called periods or rows, while the vertical columns are called families or groups. Look at a periodictable now, and distinguish the periods (rows) from the families (groups). Table 11.1 is a copy of theperiodic table which Mendeleev developed in 1871. The periodic table that was developed by Mendeleevenabled chemists to classify knowledge and concentrate their studies on physical and chemical propertiesof groups of elements rather than on each element individually. This arrangement of elements enableschemists to make predictions. These predictions are based on the repeating nature of chemicalproperties.

In problem 1 you will be asked to organize a periodic table using some fictional elements. Thefictitious elements and properties are listed in Table 11.2. You are going to enter these elements into theblocks of Table 11.3 Some of the elements have already been filled in for you. As you record eachsymbol on the periodic table, also record its mass in the lower right corner and its formula with chlorine inthe upper left corner of each block. This will make it easier to see the periodic (repeating) properties of theelements. You should use the two rules below when arranging the fictitious elements listed in Table 11.2.

RULE 1: Elements are arranged in order of increasing atomic mass from left to right in each row row.

RULE 2: Elements in each vertical column all form compounds with similar chemical formulas.

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Table 11.1Mendeleev's Periodic Table (1871)

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Problem 1. Fictitious elements, atomic masses, and chemical formulas (that show how each elementcombines with chlorine) are given in Table 11.2. On the basis of rule 1 and rule 2 mentioned earlier, youshould now arrange the elements in Table 11.2 in their proper order in the rows and columns of the"Periodic Table of Fictitious Elements" (Table 11.3). Note that some of the fictitious elements havealready been put into Table 11.3 to get you started.

Table 11.2List of Hypothetical Elements

Element Formula of Compound Atomic Mass with Chlorine (g/mole)

A A2Cl3 22B (none) 36D DCl3 44F F2Cl3 5G GCl4 31H HCl4 11J (none) 15M MCl3 9N NCl4 49P P2Cl3 39R RCl2 7S SCl2 41T (none) 52U ????? ??Z ZCl3 28

Table 11.3 A Table of Hypothetical Elements

F2Cl3

F 5

- - - -

J 15

ZCl3

Z 28

SCl2

S 41

??

? ??

Atomic Mass

Symbol

Formula with Cl

11-5 ©1997, A.J. Girondi

Look again at the completed blocks in Table 11.3. One space contains the symbol U. Study theother elements in the same column and those in the same row as U. In the spaces below give your bestestimate for the atomic mass of this unknown element and give your prediction of the formula of thecompound it will form with chlorine:

Atomic Mass of U is in the range:{1}__________________; Formula of U with Cl is: {2}______________

SECTION 11.2 Development of the Periodic Table

In science we develop models or theories to explain our observations. These models are notperfect, and most have exceptions. Mendeleev's arrangement of elements is no different. WhenMendeleev arranged elements according to similar properties, their atomic masses increased in numberfrom left to right. However, there were exceptions to this rule. Study the periodic table in your classroomor in your notebook.

Problem 2. Find two pairs of elements that appear to have their atomic masses reversed from theaccepted increasing order:

________________ and ________________; ________________ and _________________

These exceptions cast some doubt on the reliability of using atomic mass as a means of organizing theperiodic table.

Henry Moseley found the reason for this apparent exception to Mendeleev's rule. Moseleyaltered the periodic table to base it on atomic numbers rather than on atomic masses, and he restated theperiodic law so that it stated that "the properties of elements are a periodic function of their atomicnumbers." This law has no exceptions. You will learn the reason for this when you study atomic structurein an upcoming chapter.

Once again look at a periodic table in your classroom or in your notebook. There are severalthings concerning atomic numbers that are important for you to notice.

Problem 3. Answer the questions below .

a. How do atomic numbers change as you move through the periodic table? ____________________

b. Are atomic numbers whole numbers or decimal numbers? _________________

c. What element has the smallest atomic number? _________________________

d. As of June, 1995 there are 111 elements (officially). How many are listed on your table? __________

All matter, from concrete to human skin, iscomposed of either pure elements or elements incombination with each other. The proportions andkinds of elements that are combined determine whatthe particular substance is. Actually, only the first 92elements are considered natural. Those elements withatomic numbers larger than 92 are artificial elements,produced by scientists working in laboratories. Theseelements are referred to as the transuranium elements.When a new element is "discovered," other scientistsmust conduct experiments to confirm the discovery.

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Element Name Symbol

104 Unnilquadium Unq105 Unnilpentium Unp106 Unnilhexium Unh107 Unnilseptium Uns108 Unniloctium Uno109 Unnilennium Une

Table 11.4Naming New Elements

The discoverer then receives the honor of naming the new element. Precisely who discovered elements104 through 107 is questionable at this time. Russian scientists reported the production of element 104in 1964, element 105 in 1970, element 106 in 1974, and element 107 in 1976. However, Americanscientists have claimed that they produced element 104 in 1968, element 105 in 1970, and element 106in 1974. The Soviet Union has proposed the name Kurchatovium (Ku) for element 107 and Bohrium (Bh)for element 105. The United States has proposed the following names and symbols for elements 104through 109: 104 = Rutherfordium (Rf); 105 = Hahnium (Ha); 106 = Seaborgium (Sg); 107 =nielsbohrium (Ns); 108 = hassium (Hs); 109 = meitnerium (Mt).

Until the official names for elements have been agreed upon, it has been suggested that thoseelements be named according to a system which makes names out of combined Greek prefixes. (nil = 0;un = 1; quad = 4; pent = 5; hex = 6; sept = 7; oct = 8; enn = 9) The names are given a suffix of "ium."

The periodic table allows us to study groups of elements as well as individual elements. Onebroad classification of elements is by metals and nonmetals. If we study this further, we find that all metalshave several properties in common that differ significantly from the properties of nonmetals.

Problem 4. During 1994 and 1995, scientists in Germany produced elements 110 and 111. Namethem using the system described above, and give their symbols.

a. 110 name: _________________________ symbol: ___________

b. 111 name: _________________________ symbol: ___________

ACTIVITY 11.3 Metals, Nonmetals, & Metalloids - Comparing Properties

Obtain the vials from the materials shelf labeled 11.3. Three of the elements are aluminum,copper, and tin. The remaining 2 elements listed, sulfur and silicon, are classified as a nonmetals. (Siliconis also a metalloid.) Examine each sample for the properties called for in Table 11.5. The melting points ofthe substances may be found in the Handbook of Chemistry and Physics or in a similar reference book.The battery-powered device found with the vials may be used to test the electrical conductivity of eachsample. Simply touch the two wires to one piece of each element. If the device indicates that current isbeing conducted through the element, you should classify the element as having high conductivity. If itdoes not light, classify the substance as having low conductivity. The wires of the device should nottouch each other. "Phase" in Table 11.5 refers to solid, liquid, or gas. "Luster" refers to dull or metallic.

Study the information you have collected from Table 11.5 and react to the four statements below.

1. Make a general statement about the properties of a metallic substance.

______________________________________________________________________________

______________________________________________________________________________

11-7 ©1997, A.J. Girondi

Table 11.5Properties of Selected Metals and Nonmetals

Element Phase Luster Conductivity Melting Point (oC)

copper(metal)

tin(metal)

aluminum(metal)

sulfur(nonmetal)

silicon(nonmetal-metalloid)

Propose a hypothesis about why frying pans are usually made of metals while their handles are usually

made of nonmetals like wood or plastic. ________________________________________________

_____________________________________________________________________________

The melting point of a substance is related directly to its hardness. Elements with high melting points aregenerally hard substances. With this is mind, list the substances in Table 11.5 from hardest to softest.

hardest---> ____________________________________________________________<------softest

Do the hardest materials appear to be metals or nonmetals? {3}________________________________

Locate the "staircase" on the right side of the periodic table. The elements that are located to theleft of this staircase are classified as metals, while those to the right of it are nonmetals.

Are most elements metals or nonmetals?{4}______________________________________________

Name 3 metals:__________________________________________________________________

Name 3 nonmetals:_______________________________________________________________

The elements that border the staircase on the periodic table are known as metalloids. Theseelements have some properties that make them resemble metals, but other properties that make themresemble nonmetals. They include the elements just above and just below each step of the staircasestarting with aluminum (#15). A good example is silicon. Silicon is known as a "semiconductor" because itconducts electricity better than nonmetals, but not as good as metals. It is the major component ofcomputer chips.

Obtain the sample of silicon from the box of materials for Activity 11.3. While silicon is a metalloid,it falls on the nonmetal side of the staircase. Describe one property of silicon that makes it remind you of ametal:

______________________________________________________________________________

11-8 ©1997, A.J. Girondi

SECTION 11.4 The Modern Periodic Table

Dividing the elements into metals and nonmetals is only one way in which they are categorized.As mentioned earlier, another way to classify them is by families (or groups) and periods (or rows).Elements such as boron, carbon, and neon are in the same horizontal row and are said to be in the sameperiod. Elements in the same vertical column, such as lithium and sodium, belong to the same family orgroup. To distinguish the families of elements, the families (or groups) have names as well as numbers.Note in Table 11.6 that the families are numbered 1A through 8A, while the periods (rows) are numbered1,2 3, etc.

1A

2A 5A 6A 7A

8A

3A 4A

Table 11.6The “A” Families on the Periodic Table

107 108 109 110 111Unh Uns Uno Une Uun Uuu

*Some authors do not consider aluminum (#13) or Astatine (#85) to be metalloids.

The families used to be broken up into two subgroups which were labeled the "A" families and the"B" families. The transition elements in the center of the table were included in this system. You probablywill see periodic tables in your classroom or elsewhere that still use this system. However, the mostmodern labeling system now includes 18 families of elements including the transition elements. It isshown in the following partial periodic table (Table 11.7).

Some families are often named according to the first element in the family. For example, family 16above is the oxygen family, family 15 is the nitrogen family, family 14 is the carbon family, and family 13 isthe boron family. These families also have other names which are not in common use. Other familieshave commonly-used special names. Family 18 is known as the noble gases, family 17 elements areknown as the halogens, family 1 elements are called the alkali metals, while family 2 elements are known asthe alkaline-earth metals. See Table 11.8. The metals in the center block of the table are collectivelyknown as the transition metals. The two rows at the bottom of the table (the lanthanide and actinideseries) are collectively known as the rare earth elements. In Table 11.8, write in the "names" of families 13through 16.

11-9 ©1997, A.J. Girondi

Rows 6 and 7 of the periodic table are not shown here (to save space).

You have seen that metals have properties that help to distinguish them from nonmetals. In thesame way, each chemical family has a set of characteristic properties. We will be taking a closer look atsome of the properties associated with each chemical family.

Problem 5. Refer to Table 11.8 and a periodic table to help you with the following.

a. Write the symbols for the alkali metals: _______________________________________________

b. Write the symbols for the alkaline-earth metals: _________________________________________

c. Write the symbols for the halogens: _________________________________________________

d. Write the symbols for the noble gases: _______________________________________________

e. Name the elements in group IIIA (or group 13): _________________________________________

______________________________________________________________________________

f. Name the elements in group VA (or group 15):__________________________________________

______________________________________________________________________________

You have been told that the members of a family of elements have similar properties. The alkalimetals, for example, all react with water in the same proportions to form compounds that have similarchemical formulas.

Problem 6. The chemical equations below illustrate reactions between a few alkali metals and water.Complete and balance each equation. Note the similarity of the equations for the various family 1Aelements:

a. 2 Li + 2 HOH ----> 2 LiOH + 1 H2

b. _____Rb + _____HOH ------> _____RbOH + _____H2

c. _____Cs + _____HOH ------> _____CsOH + _____H2

11-10 ©1997, A.J. Girondi

Transition Metals

1A 2A 3A 4A 5A 6A 7A 8A

1 2 13 14 15 16 17 18

<----- 3 THROUGH 12 ------>

Lanthanide Series

Actinide Series

Rare-Earth Elements

Table 11.8Names of Classes and Families of Elements

transition metals

Sc Zn

ACTIVITY 11.5 Properties of Alkaline-Earth Element Compounds

One chemical family that is more easily and safely studied is the alkaline-earth metals. Find thematerials labeled 11.5 on the materials shelf. Because elements in the same families have strong familyresemblances, you can predict the chemical behavior of other family members if you know how one or twofamily members act in a chemical reaction. The experiment presented here will help to illustrate this point.Be sure to wear glasses! Use standard 150 mm test tubes.Procedure:

1. Place 5.0 mL of 0.1 M magnesium nitrate, Mg(NO3)2, solution into a test tube. Into a second test tube,place 5.0 mL of 0.1 M calcium nitrate, Ca(NO3)2, solution.

2. Add 5.0 mL of 0.1 M sodium carbonate, Na2CO3, solution to each test tube. Stopper and shake bothtubes well. Describe what happens in each tube.

3. Strontium, barium, magnesium, and calcium are all members of the same family, the alkaline-earthmetals. Suppose you had solutions of strontium nitrate, Sr(NO3)2, and barium nitrate, Ba(NO3)2. Predictwhat would happen if you mixed each of these solutions with sodium carbonate, Na2CO3, solution.

______________________________________________________________________________

11-11 ©1997, A.J. Girondi

4. What knowledge allows you to make the above prediction? ________________________________

______________________________________________________________________________

5. Test your prediction by repeating the procedure in steps 1 and 2, but this time use 0.1 M strontiumnitrate, Sr(NO3)2, solution and 0.1 M barium nitrate, Ba(NO3)2, solution. Describe the changes in detail.

______________________________________________________________________________

______________________________________________________________________________

6. Suppose you were given a test tube containing a clear liquid. How could you test it to determine if an

alkaline-earth metal were in the liquid? _________________________________________________

______________________________________________________________________________

7. Wash all tubes and put the materials and solutions back in their proper places.

ACTIVITY 11.6 The Properties of Halogen Compounds

Another group of elements that have family resemblances are the halogens. You will observesome of those similarities in this activity. Find the materials labeled 11.6 on the materials shelf. Be sure towear glasses!

Since the halogens are a family, they all react in a similar fashion with silver nitrate, AgNO3, to forma solid (precipitate). Each precipitate which forms, however, is slightly different from the others. We will betaking advantage of these differences to try to identify which halogen is present in an "unknown"solution. By comparing the reaction of the unknown halogen to the reactions of the known halogens, it ispossible to identify the unknown as being a compound of bromine, chlorine, or iodine.

1. Carry out the reactions outlined in Table 11.9. In each situation, add 1 mL of each halogen solution to 1mL of AgNO3 solution, stopper, and shake each test tube.

2. Observe any reaction that occurs, and then add 2 to 3 mL of 6.0 M NH4OH solution, stopper, and shakefor a minute. Observe any change.

3. Complete and balance each equation. (The first one has been done for you.) Identify any precipitate.Write your observations such as color of a precipitate, etc. Be certain that your test tubes and otherequipment are clean before you begin any of the combinations listed in Table 11.9.

4. Wash and rinse several times with a little distilled water if you have any doubt. Caution: handle AgNO3

with care. It can cause harmless, but dark, temporary stains on skin which do not appear until hours aftercontact.

11-12 ©1997, A.J. Girondi

Table 11.9Halogen Reactions

Reactants Products

NaCl(aq) + AgNO3(aq) ----> ____AgCl(s)____ + ___NaNO3(aq)__

Observations: ____________________________________________________________

NaBr(aq) + AgNO3(aq) ----> ______________ + ______________

Observations: ____________________________________________________________

NaI(aq) + AgNO3(aq) ----> ______________ + ______________

Observations: ____________________________________________________________

Unknown + AgNO3; Observations: ____________________________________________

Identity of unknown: _____________________________(Note: the "unknown" is one of the following: NaCl, NaBr, or NaI)

The addition of NH4OH solution caused which of the precipitates to dissolve?_____________________

1. On what evidence did you base your conclusion about the identity of the unknown? _____________

_____________________________________________________________________________

2. Based on what you learned in this activity, how might you determine if your tap water at home has

chlorine in it?____________________________________________________________________

Give it a try! Using your answer above, test some tap water and test some distilled water. Did your

hypothesis work? ________________

The reactions in Table 11.9 fall into which of the 4 major reaction types?{5}________________________ (choose either direct combination, decomposition, single replacement or double replacement)

SECTION 11.7 Other Classes Of Elements On The Periodic Table

So far, we have looked closely at two chemical families, halogens and alkaline-earth metals. Theremaining chemical families also have distinguishing properties. The large middle portion of the periodictable contains the transition metals. In general, these transition metals have higher melting points and arephysically stronger than the alkali or alkaline-earth metals. Because of this property, many of the transitionmetals such as iron, titanium, and vanadium are used in construction of buildings, aircraft, and specialtyproducts.

11-13 ©1997, A.J. Girondi

The noble gas family is composed of elements that are all gases at room temperature and are alsononmetals. The noble gases are so named because of their very nonreactive character. It was longbelieved that the noble gases would not react with any other elements. For that reason, they used to becalled the "inert" gases. But in the 1960's scientists managed to force xenon and fluorine to formcompounds under extreme conditions. Nevertheless, the noble gases are the least reactive elements onthe periodic table. In the next chapter you will learn why they behave this way.

The elements in the lanthanide series and the actinide series are also metals. Together they areknown as the rare-earth elements. The lanthanides all have similar chemical and physical properties.These elements are relatively common, but because of the difficulty in separating them from each other,they are not commonly available. Among the actinides, all of which are radioactive, only uranium andthorium exist in any significant amounts in nature. The other actinides were discovered and observed asthe products of controlled nuclear reactions and, in many cases, have been produced in only very smallamounts. Uranium and thorium are used as fuel in nuclear reactors and in the warheads of nuclearweapons.

Both the lanthanide and the actinide series actually belong up in rows 6 and 7 of the periodictable. If you follow the atomic numbers of the elements, you will see where these two series actually fit.However, if we put them there, they would make the periodic table rather long. So, to make the wholething more compact, we take these two series out and put them at the bottom.

The lanthanides and actinides actually fit into the periodic table between what two families or

categories of elements? {6}_________________________________________________________

Within the major chemical families, chemists have had some difficulty in finding a proper place forone element in particular. This element is hydrogen. In most periodic tables, hydrogen is placed in Family1A (or group 1) above lithium. But, you have seen that the elements in that family are metals. Hydrogen iscertainly not a metal, so this placement seems a bit odd. Hydrogen shares some of its physicalcharacteristics with the halogen family. But, hydrogen has little in common with the halogens in terms of itschemical properties. To help resolve this problem, hydrogen is often placed in both family 1A and 8A(groups 1 and 17). Some periodic tables show hydrogen above family 1A, but it is detached as if to pointout its uniqueness.

ACTIVITY 11.8 Making, Collecting, and Studying Hydrogen Gas

This experiment will familiarize you with some of the properties of hydrogen. It is hazardous,however, and you must be closely supervised and observed by the teacher as you do this. Be sure tonotify the teacher before you begin, and have your set-up checked before you actually generate any gas.

1. Get the materials labeled 11.9 from the materials shelf. Set up the apparatus as shown in Figure 11.1below. Be sure to wear safety glasses and an apron.

2. Have the teacher check your set-up before going any further. All connections must be snug to preventhydrogen gas from escaping.

3. Fill three or four 150 mm (regular size) test tubes with water, put your thumb on top and carefully invertthem into the trough so that little or no water is lost. Keep all flames and sparks away from your set-up!!Add 10 mL of 3 M hydrochloric acid (HCl) to the flask containing 4 to 5 grams of mossy zinc, and then insertthe rubber stopper assembly.

11-14 ©1997, A.J. Girondi

water level

150 mm test tube filled with water

HCl + Zn

bubbles of H2 gas

metal shelf

pneumatic trough

Figure 11.1 Collection of Hydrogen Gas by Water Displacement

Overall reaction: 2 HCl + Zn ---> ZnCl2 + H2

4. When the hydrogen gas starts to form in the flask, allow the gas to bubble for a minute or so to force airout of the flask and rubber tubing before attempting to collect any gas in a test tube. Then, collect gas inthe test tubes by placing the end of the tubing under the mouth of each tube until all of the water hasbeen forced out. If the gas stops before you have collected enough, add more HCl to the flask.

5. Store the tubes upside down inverted in the water or on your desk after they are full of gas. When youhave collected enough gas to fill the test tubes, you can stop the generator by adding water to the flask.

6. Pour the diluted acid into a sink, and throw the zinc into the refuse can. To test the tubes for thepresence of hydrogen, get away from your hydrogen generator and light a wooden splint (don't light anyburners close to your equipment!). Quickly move the flaming splint next to the mouth of one of yourinverted test tubes. (Keep it away from the others.) Repeat the procedure with the remaining tubes ofgas.

1. Describe what happens._________________________________________________________

2. Why did you store the tubes of H2 gas upside down? {7}__________________________________

3. Hydrogen explodes by reacting with oxygen gas in the air to form water vapor. Write the balancedequation for the reaction which occurred when the contents of the tube met the burning splint.

{8}__________________------>__________________

Return all of your equipment to the materials shelf. Rinse the tubes and flask.

SECTION 11.9 Using the Periodic Table to Predict Properties and Formulas of Compounds

One of the factors that gave validity to the arrangement of elements on the periodic table was thatit enabled chemists to predict the properties of several undiscovered elements. In the table below youcan see how well Mendeleev was able to predict the properties of an undiscovered element which hecalled "ekasilicon," which turned out to be what we now call germanium. The property which Mendeleev

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described as combining power in the table above refers to the number of bonds an atom forms with otheratoms. This predictive power can be very useful in determining the chemical formulas of substances.

Look at the formulas of the Group 1 (Family 1A) elements combined with chlorine and brominebelow.

Chlorides: LiCl NaCl KCl RbCl CsCl FrClBromides: LiBr NaBr KBr RbBr CsBr FrBr

Notice how all group 1 (family 1A) elementscombine with group 17 (family 7A) elements in a1:1 ratio. It is possible to use the periodic table tomake predictions in the same way thatMendeleev did. Once you know the formulas ofcompounds of an element, you can predict theformulas of similar compounds. Look at theformulas of chlorides formed by elements infamilies 1A - 7A (groups 1,2 & 13-17) as shown inTable 11.11.

Table 11.10Mendeleev's Predictions About

"Ekasilicon"

Property Prediction Actual Value

atomic mass 72 72.59density (g/cm3) 5.5 5.32 combining power 4 4specific heat (J/g.oC) 0.305 0.322

How many Cl's are attached to each of the column 1A elements shown above? {9}__________________

How many Cl's are attached to each of the column 4A elements? {10}____________________________

We can state this general principle:

Given the formula of a compound, the replacement of an element in the compound byanother element from the same family will often give the correct formula for anothercompound.

For example, beryllium chloride has the formula BeCl2. What is the formula for magnesium chloride? Sincemagnesium is in the same family as beryllium, the formula will be MgCl2.

Note also that when chlorine is combined with chlorine, it is shown as Cl2. You should recall thatthere are seven diatomic elements. All of the halogens (F2, Cl2, Br2, I2) and elemental gases (H2, N2, O2)do this. Two atoms are bonded together when these elements exist in a free form. You will soon learnwhy this is.

Table 11.11Chorine Compounds of the “A” Family Elements

(1) (2) (13) (14) (15) (16) (17) (18)1A 2A 3A 4A 5A 6A 7A 8A

LiCl BeCl2 BCl3 CCl4 NCl3 OCl2 FCl - - - -NaCl MgCl2 AlCl3 SiCl4 PCl3 SCl2 Cl-Cl - - - -KCl CaCl2 (Cl-Cl can also be written as Cl2)

Note: Table 11.11 will make more sense to you when you learn more about atomic structure in the next few chapters.

11-16 ©1997, A.J. Girondi

Problem 7. Bromine belongs to the same family as chlorine. Based on the principle given above,complete Table 11.12 below by writing formulas for bromide compounds of the "A" family elements which"belong" in the blank spaces. A few have already been written for you.

1A

2A 3A 4A 5A 6A 7A

8A

LiBr

CaBr2

CBr4

Table 11.12Bromine Compounds of the "A" Family Elements

Zinc, cadmium, and mercury all belong to the same family in the periodic table. The formulas and names ofcertain zinc compounds are: Formula Name

ZnO zinc oxide Zn(NO3)2 zinc nitrate ZnS zinc sulfide ZnCl2 zinc chloride

Problem 8. Since cadmium and mercury are in the same family as zinc, you should be able to predict theformulas of similar compounds formed with mercury and cadmium. Do this below.

a. cadmium oxide __________ mercury (II) oxide __________

b. cadmium nitrate __________ mercury (II) nitrate __________

c. cadmium sulfide __________ mercury (II) sulfide __________

d. cadmium chloride __________ mercury (II) chloride __________

The periodic table gives us a useful method for predicting chemical formulas. You will have abetter understanding of why this all works after you study atomic structure in the upcoming chapter.(Since atomic structure was unknown in his time, Mendeleev never did understand why this predictingpower of the periodic table works!)

The periodic table, however, is not flawless as a predictor. For example, if carbon monoxide, CO,were used as a reference, you would predict that the compound carbon sulfide, CS, would also exist - itdoes not. (Oxygen and sulfur are in the same family.) Even though your predictions may not be 100%correct, this general principle is very useful. It allows you to make predictions based on a small amount ofinformation.

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Problem 9. In this problem, you are given several chemical names and formulas. Predict the formula ofthe compound asked for. In order for predictions to be possible, however, elements must be members ofthe same family on the periodic table. In the first example, Na and Cl are in the families 1A and 7A. K andBr are also in families 1A and 7A. This means they will form compounds with similar chemical formulas.

Given: Predict the formula for:

a. sodium chloride: NaCl potassium bromide: ____KBr____

b. magnesium chloride: MgCl2 calcium iodide: ___________

c. calcium sulfate: CaSO4 magnesium sulfate: ___________

d. barium hydroxide: Ba(OH)2 calcium hydroxide: ___________

e. chlorine: Cl2 iodine: ___________

f. silver nitrate: AgNO3 copper (I) nitrate: ___________

g. carbon dioxide: CO2 silicon dioxide: ___________

h. beryllium sulfide: BeS strontium oxide: ___________

Problem 10. For more practice, underline the substance in the right column that would be more likelyto exist after comparing the choices to a known substance in the left column.

Known Substance Possible Substances

a. SF6 ClF6 or TeF6 b. PCl5 AsCl5 or GeCl4c. WCl6 WS6 or WBr6d. Na2SiF6 K2SiCl6 or NaPF6

e. K2SO4 Mg2SO4 or Na2SO4

f. Na2CO3 K2CO3 or Ca2CO3

Problem 11. Given the chemical formulas below, predict the likely chemical formula for the followingsubstances.

Given Predict the formula for:

a. CaCO3 a carbonate of magnesium _____________(calcium carbonate)

b. Na3PO4 a phosphate of potassium _____________(sodium phosphate)

c. CO2 a silicon-oxygen compound _____________(carbon dioxide)

d. Na2CrO4 a chromate of potassium _____________(sodium chromate)

11-18 ©1997, A.J. Girondi

e. InPO4 a phosphate of aluminum _____________(indium phosphate)

f. PbCl2 a bromide of silicon _____________(lead (II) chloride)

g. MgCrO4 a calcium chromate compound _____________(magnesium chromate)

h. K2SO4 a sulfate of sodium _____________(potassium sulfate)

i. SiF4 a chloride of carbon _____________(silicon tetrafluoride)

j. Na3PO4 a lithium phosphate compound _____________(sodium phosphate)

ACTIVITY 11.10 Reactions of Sodium and Potassium With Water

-> -> -> -> TEACHER DEMONSTRATION <- <- <- <-

Hydrogen is very explosive and will ignite when heated sufficiently. The reactions between thealkali metals and water (see problem 6) occur very rapidly and release a great deal of heat. In fact, the heatgiven off by some of these reactions is enough to ignite the gas. These metals are often stored in oil orkerosene to prevent them from reacting with air or water. Even the moisture in air may be sufficient tocause an explosion under certain circumstances.

The point is that these metals all behave in a similar way. There is, however, a difference in the"activity" of these metals in water. Some react more vigorously than others. To demonstrate this, yourteacher will demonstrate for you the reaction of sodium and potassium with water. He will put somephenolphthalein in the water and then add the metal. The phenolphthalein will turn pink if a hydroxidecompound forms (such as NaOH or KOH). A fizzing action will illustrate the production of the hydrogen.Stand back! The equations for the reactions are:

2 Na(s) + 2 HOH(l) ----> 2 NaOH(aq) + H2(g)

2 K(s) + 2 HOH(l) ----> 2 KOH(aq) + H2(g)

1. How were the reactions of sodium and potassium with water similar?

______________________________________________________________________________

______________________________________________________________________________

2. How were the two reactions different? _______________________________________________

______________________________________________________________________________

11-19 ©1997, A.J. Girondi

SECTION 11.11 Learning Outcomes

Knowing how to use the periodic table is a must for students of chemistry. To check yourfamiliarity with the use of information contained in the periodic table, review the learning outcomes below.When you are sure you have mastered an outcome, check the box in front of it. Arrange to take the examon Chapter 11, and go on to Chapter 12.

_____1. Describe the general organization of the modern periodic table based on Moseley's periodic law.

_____2. Explain what is meant by periods (also called rows or series) and groups (also called families).

_____3. Describe the general properties of metals and nonmetals, and show their location on the periodic table.

_____4. Indicate the position on the periodic table of the alkali metals, the alkaline-earth metals, the halogens, the noble gases, the transition metals, the lanthanide series, and the actinide series.

_____5. Predict the physical properties of an element given those of its neighbors and "family members"on the periodic table.

_____6. Predict the chemical formulas of compounds given those of similar compounds.

11-20 ©1997, A.J. Girondi

SECTION 11.12 Answers to Questions and Problems

Questions:

{1} between 22 and 28; {2} UCl2; {3} metals; {4} metals; {5} double replacement; {6} between thealkaline-earth metals and the transition metals; {7} hydrogen is less dense than air;{8} 2 H2(g) + O2(g) ----> 2 H2O(g); {9} one; {10} four

Problems:

Table 11.3 A Table of Hypothetical Elements

F2Cl3

F 5

- - - -

J 15

ZCl3

Z 28

SCl2

S 41

A2Cl3

22

AP2Cl3

P 39

RCl2

R 7

MMCl3

9

DCl3

D 44

- - - -

B 36

- - - -

T 52

HCl4

H 11

31

GCl4

GNCl4

N 49

UCl2

Ubetween 22 and 28

1.

2. Cobalt (#27) and Nickel (#28); Tellurium (#52) and Iodine (#53); and there are more.3. a. increase; b. whole; c. hydrogen; d. (varies)4. a. ununnilium, Uun; b. unununium, Uuu5. a. Na, Li, K, Rb, Cs, Fr; b. Be, Mg, Ca, Sr, Ba, Ra; c. F, Cl, Br, I, At; d. He, Ne, Ar, Kr, Xe, Rn;

e. boron, aluminum, gallium, indium, thallium; f. nitrogen, phosphorus, arsenic, antimony, bismuth6. a. (given)

b. 2 Rb + 2 HOH ----> 2 RbOH + H2

c. 2 Cs + 2 HOH ----> 2 CsOH + H2

7. LiBr, BeBr2, BBr3, CBr4, NBr3, OBr2, FBr, - - -;NaBr, MgBr2, AlBr3, SiBr4, PBr3, SBr2, ClBr, - - -;KBr, CaBr2;

8. a. CdO, HgO; b. Cd(NO3)2, Hg(NO3)2; c. CdS, HgS; d. CdCl2, HgCl29. a. KBr; b. CaI2; c. MgSO4; d. Ca(OH)2; e. I2; f. CuNO3; g. SiO2; h. SrO10. a. TeF6; b. AsCl5; c. WBr6; d. K2SiCl6; e. Na2SO4; f. K2CO3

11. a. MgCO3; b. K3PO4; c. SiO2; d. K2CrO4; e. AlPO4; f. SiBr2; g. CaCrO4; h. Na2SO4; i. CCl4;j. Li3PO4

11-21 ©1997, A.J. Girondi

SECTION 11.13 Student Notes

11-22 ©1997, A.J. Girondi