NAME____________________________________ PER____________ DATE DUE____________

ACTIVE LEARNING IN CHEMISTRY EDUCATION

"ALICE"

CHAPTER 5

ATOMSAND

MOLECULESAtomic Theory

Naming CompoundsWriting Formulas

5-1 ©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

5-2 ©1997, A.J. Girondi

SECTION 5.1 The Classification Of Matter

In order to work effectively with chemical concepts, it is important for you to learn the "language ofchemistry" and how certain words and symbols are used by chemists. In this chapter you will learn aboutthe meaning of terms such as element, compound, mixture, atom, molecule, ion, and polyatomic ion (orradical). You will also learn to identify chemical elements by chemical symbols. Finally, you will learn howto write chemical formulas and how to name chemical compounds. An idea that can be attributed to theancient Greeks is the concept of the atom. They developed the idea that all of the material substance inthe world was composed of fundamental building blocks that could not be divided into smaller parts. Theproperty of being indivisible into smaller parts led them to coin the word atom, which means "indivisible."Today, we realize that atoms can be broken up into smaller pieces, but the name atom is still used todescribe the fundamental unit of matter for chemists. Atoms have the special ability to combine togetherto form larger groups of atoms called molecules. Two types of molecules are possible - elements andcompounds. When a molecule is composed of only one kind of atom, it is referred to as an element. Forexample, the element gold is composed of millions of gold atoms connected together. A sample of themetal copper is made of copper atoms linked together. Atoms of some elements tend to combine in pairs.These paired elements are called diatomic molecules. Diatomic means "two atoms" in a molecule.Elements that exist as diatomic molecules include hydrogen and oxygen. In the pure form they are writtenas H2 and O2. You will learn about other diatomic gases in chapter 6.

The idea that substances in nature are composed of certain basic or fundamental elements thatcannot be further reduced to simpler substances is an ancient one dating back to early Greece. TheGreek elements were considered to be earth, air, fire, and water. Today, we realize that nature is muchmore complex than that. Of the first 92 elements, 90 are naturally-occurring ones of which all other matteris composed. Technitium (#43) amd promethium (#61) are the exceptions. We have also been able toproduce at least an additional 19 elements in the laboratory. These are called human-made elements.They are more complicated than the basic ninety-two and are very unstable, which means theydecompose readily into simpler elements. A listing of all of the elements is undoubtedly presentsomewhere in your chemistry classroom. This list is called the periodic table of elements. Each elementon the table is represented by a symbol.

In instances where molecules are composed of more than one kind of atom, this cluster of atomsis referred to as a compound. Examples of compounds include water (H2O), carbon dioxide (CO2), andtable salt (NaCl). Although these substances consist of more than one kind of atom, they are consideredto be pure substances. Elements are also considered to be pure substances.

A mixture is yet another way to describe combinations of elements and compounds. A mixture iscomposed of materials that have been placed together but which are not chemically combined. A mixturemay be composed of elements or compounds. The important thing to remember is that the substancesmaking up a mixture can always be separated by physical methods which means without using a chemicalreaction. Sand and salt can be made into a mixture by simply stirring these two substances together. Thesand and salt mixture can then be separated by adding water and filtering. The salt will dissolve in thewater and pass through the filter paper, while sand would not be able to pass through the filter paper.Dissolving is a physical change and filtering is a physical method of separation. The next activity will help toillustrate the difference between a mixture and a compound. Homogeneous materials are those whichhave the same composition throughout. Heterogeneous materials do not have the same compositionthroughout. Solutions such as salt water are homogeneous mixtures since they have the samecomposition throughout and can be separated by physical methods (such as boiling the water away). Themineral called marble is an example of a heterogeneous mixture since its composition can vary, evenwithin one small sample as well as from one location to another on earth.

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Matter

Pure SubstancesMixtures

Homogeneous Heterogeneous Elements Compounds

Solutions

Figure 5.1 The Classification of Matter

ACTIVITY 5.2 Properties Of Iron In A Compound And In A Mixture

Obtain the materials labeled 5.2 from the materials shelf. Container A contains iron filings andpowdered sulfur mixed together. Container B contains a chemical compound containing iron, sulfur, andoxygen (FeSO4). In the compound, iron is chemically bonded to the other elements.

1. Hold a magnet up to each container and move it around. One of the properties of elemental iron is thatit is attracted to a magnet.

2. Is the iron in container A attracted to the magnet?__________ Is the iron in container B attracted to

the magnet?__________ Based on your observations, do elements retain their original properties when

they form compounds with other elements? {1}__________ How does this activity support your

conclusion? {2}________________________________________________________________

______________________________________________________________________________

SECTION 5.3 Symbols Of The Elements

Each chemical element has a name assigned to it for the purpose of identifying it. The names forthe elements have been developed as each element has been discovered, and there are manyinteresting and colorful names. In order to avoid having to write a long name in describing an element, ithas become customary in chemistry to use a chemical symbol in place of the name. Most of the symbolsare derived from the names of the elements themselves.

Quite often, the symbol consists of two letters that are the first two letters in the name of theelement. As an example, the element calcium is denoted by the symbol Ca. Another example is argon,which is denoted by the symbol Ar. However, there are exceptions to this practice. The element arsenicis denoted by the symbol As so that it is not confused with argon. Another exception in chemical symbolsis the fact that some elements are denoted by only one letter. Thus, hydrogen is represented by H,oxygen by O, fluorine by F, and so on. In addition, the symbols for some of the elements are not related totheir more modern names but have come from older names for those elements that are no longer used.

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An example is sodium which has the symbol Na. This symbol is derived from the older name "natrium" thatwas originally given to sodium. Other examples of this are potassium, K; mercury, Hg; iron, Fe; tungsten,W; etc.

Table 5.1 contains the names and symbols for 38 of the more common elements. You areexpected to MEMORIZE the names of these elements and their symbols. (Spelling counts!) Manystudents misspell the name of the element which has the symbol F. Write its name - spelled properly - in

this space: _____________________ Remember, the symbol of this element is F - not Fl! And, it is notspelled flourine!

You will notice that the first letter in the symbol of any element is a capital letter, while the secondletter (if there is one) is in lowercase. You need to use care in writing the symbols. As an example, theelement cobalt has the symbol Co. If you were to write CO as the symbol for cobalt, you would actually bewriting the formula for a compound, carbon monoxide, which is very different from cobalt.

Table 5.1 Selected Elements And Their Symbols

Aluminum Al Lithium LiAntimony Sb Magnesium MgArsenic As Manganese Mn Barium Ba Mercury Hg Bismuth Bi Nickel NiBromine Br Nitrogen NCalcium Ca Oxygen OCarbon C Phosphorus PCesium Cs Platinum Pt Chlorine Cl Potassium KChromium Cr Silicon Si Cobalt Co Silver Ag Copper Cu Sodium Na Fluorine F Strontium Sr Gold Au Sulfur S Hydrogen H Tin SnIodine I Titanium Ti Iron Fe Tungsten W Lead Pb Zinc Zn

SECTION 5.4 Atomic Theory

Although the Greeks invented the idea of the atom about 2,500 years ago, their concept was notbased on experimental evidence gathered in a laboratory. Our modern atomic theory is the result of thework of several European scientists dating back to the 1600's. The most notable among these scientistsis John Dalton, an Englishman. Isaac Newton and Robert Boyle, two other Englishmen, had suggestedthe possibility of atoms through their work, but Dalton put the idea of the existence of atoms on a firmexperimental basis.

Dalton was able to show that when elements combined to form compounds, the masses of eachelement that went into making a compound always were present in definite ratios to each other. Thus,when he combined hydrogen with oxygen to form water, he always found that the ratio of the mass of

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hydrogen to that of oxygen was 1:8 (1 gram of H to 8 grams of O). This convinced him that the only way for

1 gram ofhydrogen

8 grams ofoxygen

9 grams ofwater

+this to make sense was if each element consisted of basic units, or atoms, that had definite masses.According to his reasoning, if basic units of matter did not exist, then1 gram of hydrogen should be able tocombine with any number of grams of oxygen.

John Dalton assumed that water consisted of one hydrogen atom and one oxygen atom.Furthermore, he reasoned that if the hydrogen atom had a mass of one mass unit, then the oxygen atommust have a mass of eight mass units.

+H O HO Really ? ? ?(He was incorrect, of course, in his assumption, because we now know that two atoms of hydrogencombine with one atom of oxygen to form a single molecule of water.) Water is H2O, not HO. Now if themass ratio is 1 to 8 ( H to O) in water, and if the atom ratio is 2 to 1 in water , what this means is that theoxygen atom must have a mass which is 16 times greater than that of the hydrogen atom – not 8 times asgreat (as Dalton had assumed).

Amedeo Avogadro (whom you will learn about later) recognized the problem in Dalton'sassumptions through his work with the gas laws and was able to show that certain elements, includinghydrogen and oxygen, actually existed in molecular (diatomic) form (H2 and O2). When water is formed,two molecules of hydrogen (which is four atoms of hydrogen) react with one molecule of oxygen (which istwo atoms of oxygen) to form two molecules of water:

2 H2 + O2 -----> 2 H2O

Nevertheless, Dalton's work represented the pioneering effort to experimentally establish the existenceof atoms. Dalton was also aware that two elements can produce two completely different compounds. Forexample, carbon can combine with oxygen to form either CO (carbon monoxide) or CO2 (carbon dioxide).He found that in CO, 16 parts by weight of oxygen always combined with 12 parts by weight of carbon. InCO2, he found that 32 parts by weight of oxygen always combined with 12 parts by weight of carbon. So,if he started with two equal weights of carbon and reacted them both with different quantities of oxygenhe always ended up with either a 12:16 ratio or a 12:32 ratio:

CO12 grams carbon

16 grams oxygen

CO212 grams carbon

32 grams oxygen

If you take enough of eachcompound such that the mass ofone element in them is the same

then the mass of the other element presentin the two compounds will be in a ratio ofsmall whole numbers (1:2 in this case)

Notice in the example above that for oxygen, 16 to 32 is a 1 to 2 ratio. This seemed to indicate thatelements could not combine in just any quantities. 12 grams of carbon have to combine with 16 grams ofoxygen or with 32 grams of oxygen - nothing in between! For example, he never found 12 parts by weightof carbon combining with 24 parts by weight of oxygen. Wonder why? Maybe, he reasoned, it's becauseelements don't come in just any quantity. Maybe they come in definite discrete amounts or particles. Thiswould explain the simple whole number ratio for oxygen (1:2 in this case). He called this regularity in theway two elements can combine his law of multiple proportions. This law together with the law of definitecomposition served as strong evidence suggesting the existence of atoms.

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This can all sounds somewhat confusing, so here is an analogy. Suppose you go into an icecream store and order a dish of chocolate and vanilla. When it comes you measure the mass of the icecream to make sure you are not being cheated (you just happen to have a balance with you). You find thatthe dish contains 100 grams of vanilla and 100 grams of chocolate. Since you like chocolate so much, yousend the dish back to the kitchen for more chocolate. This time when you get it back it contains 100 gramsof vanilla and 200 grams of chocolate. Hmmm. That's interesting. Exactly a 2:1 ratio between the originalamount of chocolate and the new amount. You repeat the order once more, and when you get the dishback it contains 100 grams of vanilla (starting to melt) and 300 grams of chocolate. Hey. Now thechocolate has varied in a 1:2:3 ratio - a ratio of small whole numbers. Whole numbers, mind you! Why?This leads you to believe that maybe the ice cream comes in discrete amounts - not just any amount. Afterall, the chocolate did not increase by fractional amounts. You ask the waiter if this might be true, and sureenough, the ice cream does come in discrete amounts! They are called scoops. Ah! The scoop theory ofice cream. Brilliant! See the analogy to Dalton's reasoning? Ice cream comes in scoops, while elementscome in the form of atoms!

Law of Multiple Proportions: Sometimes the same two elements can combine in differentproportions to form different compounds. (Example: CO and CO2) When they do this, ifyou hold the mass of one element in the compounds constant, the mass of the otherelement present will vary in a ratio of small whole numbers.

Dalton's atomic theory, first conceived in 1803, can be summarized by the following four statements:

1. An element is composed of extremely small particles called atoms.2. All atoms of a given element are identical to all other atoms of that element, but differ from atoms of

other elements.3. Atoms are indivisible and cannot be created or destroyed or changed into atoms of another element.4. Chemical changes take place when atoms of elements combine with each other in new ways.

Dalton's original theory was not entirely correct. For example, he thought that all atoms of a given elementhad exactly the same mass. Today, we know that atoms of an element do not all have the same mass. Wehave discovered the existence of isotopes, which are atoms of an element which have different masses.

As you have discovered, elements are represented by their chemical symbols. These symbolsare also used to describe chemical compounds that are formed when the elements react with each other.The use of these symbols to describe chemical compounds results in a chemical formula for thecompound. This formula contains the appropriate symbols and, in addition, also has small numbers writtenas subscripts (below the element) that indicate how many of each kind of atom are present in a molecule ofthe compound. The chemical formula for water is H2O. This formula means that in the water molecule,there are two hydrogen atoms and one oxygen atom. (When only one atom is involved, it is customary notto write a subscript "1" below the element.) In other words, when there is no number, it is understood thatthere is only one atom of that type present. Some compounds contain only two elements and these arecalled binary compounds. Other compounds contain more than two elements. As an example, theelements copper (Cu), sulfur (S), and oxygen (O) combine to form a compound with the chemical formulaCuSO4. In this compound for every one atom of copper, there is one atom of sulfur and four atoms ofoxygen.

Problem 1. Using the same idea, how many atoms of calcium are there in calcium chromate, CaCrO4?

Calcium?__________ Chromium?__________Oxygen?__________.

Problem 2. The formula for sodium acetate is NaC2H3O2. How many atoms of each element are present

in one sodium acetate molecule? Sodium?_________ Carbon?__________ Hydrogen?__________

Oxygen?__________.

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SECTION 5.5 Oxidation Numbers Of Elements and Polyatomic Ions

We are now at the point where you are ready to learn how to write the formulas for chemicalcompounds. In order to accomplish this task, we will be using what are known as oxidation numbers. Youwill not understand where these oxidation numbers come from until you study atomic structure in a laterchapter, but you will be able to use them, nonetheless. A list of some common oxidation numbers forselected elements can be found in Table 5.2 below. There are other oxidation numbers for theseelements besides those listed here, but this list will suit your purposes for now.

Table 5.2 Common Oxidation Numbers of Selected Elements(Note: Sometimes these elements can assume oxidation numbers other than those listed.)

Aluminum Al +3 Lithium Li +1Antimony Sb +3,+5 Magnesium Mg +2Arsenic As +3,+5 Manganese Mn +2,+4,+7Barium Ba +2 Mercury Hg +1,+2Bismuth Bi +3 Nickel Ni +2Boron B +3 Nitrogen N -3,+3,+5Bromine Br -1,+5 Oxygen O -2Calcium Ca +2 Phosphorus P +3,+5Carbon C +2,+4 Platinum Pt +2,+4Cesium Cs +1 Potassium K +1Chlorine Cl -1,+5,+7 Silicon Si +4Chromium Cr +2,+3,+6 Silver Ag +1Cobalt Co +2,+3 Sodium Na +1Copper Cu +1,+2 Strontium Sr +2Fluorine F -1 Sulfur S -2,+4,+6Gold Au +1,+3 Tin Sn +2,+4Hydrogen H +1 Titanium Ti +3,+4Iodine I -1,+5 Tungsten W +6Iron Fe +2,+3 Zinc Zn +2Lead Pb +2, +4

(A copy of Table 5.2 (oxidation numbers) which you will be permitted to use during tests and quizzes canbe found in the Reference Notebook which you were given as a part of ALICE.) You do NOT need tomemorize Table 5.2.

Common oxidation numbers for other elements can be found on some periodic tables and inother reference sources. Remember, you do not need to memorize oxidation numbers. Table 5.2contains the most commonly used oxidation numbers of the elements listed. It is possible that sometimesan element will exhibit an oxidation number which is not listed in the table.

There is yet another kind of fundamental unit present in some substances called an ion. An ion isa particle that carries an electric charge. In certain specific events that happen in chemistry, atoms ormolecules can end up with a positive (+) or negative (-) charge. These atoms or molecules then becomeions. Another name for ions which contain more than one atom is a polyatomic ion (they used to be calledradicals). Examples of ions include H1+, OH1-, NH41+, and SO42-. Ions like SO42- can also be written asSO4-2. It means the same thing. The ion has a charge of minus two.

There are oxidation numbers for polyatomic ions (see table 5.3). You ARE required to commit thislist (Table 5.3) to MEMORY including the names, the formulas, and the charges!

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A table of polyatomic ions (like Table 5.3) can also be found in your ALICE Reference Notebook.You will be given a quiz to insure that you have learned the names, formulas, and charges of thepolyatomic ions. After that quiz, you will be allowed to refer to the list of polyatomic ions in your referencenotebook during future tests and quizzes. The reason for having you memorize them is to help you torecognize them as polyatomic ions when you see them. When you write polyatomic ions, you should writethe charge with the formula. For example, sulfate should be written as SO42-, while permanganate shouldbe written as MnO41-, etc. This list is not complete. There are many other polyatomic ions besides thoselisted in Table 5.3.

Table 5.3Common Oxidation Numbers of Selected Polyatomic Ions

Name Formula Charge

Ammonium NH41+ +1Acetate C2H3O21- -1 Chlorate ClO31- -1Perchlorate ClO41- -1 Cyanide CN1- -1 Hydrogen carbonate HCO31- -1 (or bicarbonate) Hydrogen sulfate HSO41- -1 Hydroxide OH1- -1 Nitrate NO31- -1 Nitrite NO21- -1 Permanganate MnO41- -1 Thiocyanate SCN1- -1Carbonate CO32- -2 Chromate CrO4 2- -2 Dichromate Cr2O72- -2 Sulfate SO42- -2 Sulfite SO32- -2Phosphate PO43- -3

SECTION 5.6 Writing Formulas for Chemical Compounds

The process of writing a chemical formula using oxidation numbers is really rather simple. The onerule that you must remember is that

"the sum of the oxidation numbers of the atoms in the formula of a compound must be zero."

For example, hydrogen's oxidation number is +1 and oxygen's is -2. Therefore, in order for the oxidationnumbers to add up to zero, we need two hydrogens. Two hydrogens = +2 and one oxygen = -2, so theformula for water is H2O. The subscript "2" to the right of the H indicates the presence of two hydrogenatoms. When a symbol is present without a subscript to its right, we assume that a subscript of "1" is there.We don't actually write the subscript if it is a one. Notice, too, that the element with the positive oxidationnumber is usually written first. Let's try more.

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Example 1: What is the formula for a compound of calcium and chlorine? Ca = +2 and Cl = -1. Therefore,in order for the oxidation numbers to add up to zero, these two elements must combine in a one to tworatio: CaCl2

Example 2: What is the formula for a compound of aluminum and oxygen? Al = +3 and O = -2. Therefore,in order for the oxidation numbers to add up to zero, these two elements must combine in a two to threeratio: Al2O3

One method used to write formulas involves the use of a lowest common multiple (LCM). Inexample 1 above, the lowest common multiple (disregard the signs) of the two oxidation numbers (+2 and-1) is 2. Now divide each oxidation number into the lowest common multiple (LCM) to determine thesubscript for that element in the formula. For Ca: 2/2 = 1; and for chlorine: 2/1 = 2. Therefore, the formula isCaCl2. In the case of example 2 above, the LCM of the oxidation numbers involved (+3 and -2) is 6. Foraluminum: 6/3 = 2; and for oxygen: 6/2 = 3. So, the formula for the compound is Al2O3. Notice how thesum adds up to zero! [2 Al = +3 X 2 = +6; 3 O = -2 X 3 = -6]. Then, (+6) + (-6) = 0. Practice now by doingproblem 3.

Problem 3. Using oxidation numbers from Tables 5.2 and 5.3, write correct formulas for compounds ofthe following substances. Keep in mind that if one element has only a positive oxidation number, youmust use a negative oxidation number for the other element. Some elements have more than oneoxidation number. So, when you see a symbol followed by a Roman numeral in parentheses in theproblems below, the Roman number equals the oxidation number which you should use for that element.Iron has two oxidation numbers: +2 and +3. Fe(II) refers to Fe2+.

Example: Manganese can be +2, +4, or +7. Mn(IV) = Mn4+. See? The oxidation number is the same asthe Roman numeral. Note, however, that the Roman numeral is not used in the formula. For example,when Mn(IV) and Cl combine, the compound's correct formula is MnCl4. It is incorrect to include theRoman numeral in the name. Therefore, Mn(IV)Cl4 is WRONG!

a. Ba and Cl _______________ i. Cu(I) and S _______________

b. Hg(I) and Br _______________ j. As(V) and O _______________

c. Ca and O _______________ k. C(IV) and O _______________

d. Hg(II) and Cl _______________ l. Sn(IV) and Br _______________

e. Al and S _______________ m. P(III) and I _______________

f. Ag and S _______________ n. As(V) and Cl _______________

g. N(III) and O _______________ o. Sn(II) and F _______________

h. Na and O _______________ p. Sr and Br _______________

This same method is used when the formula you are trying to write contains a polyatomic ion. Justkeep in mind that polyatomic ions stay together as a group and act as though they were a single atom witha single oxidation number. Whenever more than one polyatomic ion appears in a formula, it must beenclosed by parentheses with a subscript outside.

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Example 3: Write the formula for a compound of potassium and permanganate. K = +1 and MnO41- = -1.LCM = 1, so, the formula for potassium permanganate is KMnO4.

Example 4: Write the formula for a compound of calcium and chlorate. Ca = +2 and ClO31- = -1. LCM = 2 So, the formula for calcium chlorate is Ca(ClO3)2

Example 5: Write the formula for a compound of ammonium and sulfate. NH41+ = +1 and SO42- = -2.LCM = 2, so, the formula for ammonium sulfate is (NH4)2SO4 .

Problem 4. Write correct formulas for compounds of the following:

a. Mg and SO42- _______________ g. Al and SO32- _______________

b. Sn(II) and CrO42- _______________ h. Zn and CO32- _______________

c. Na and HCO31- _______________ i. Cu(II) and OH1- _______________

d. Fe(II) and OH1- _______________ j. Fe(III) and SO42- _______________

e. Pb(II) and PO43- _______________ k. Hg(I) and NO31- _______________

f. NH41+ and Cl1- _______________ l. NH41+ and Cr2O72- _______________

Check your answers for problem 4, and then try problem 5 below.

Problem 5. Write correct formulas for compounds of the following:

a. Mg and F _______________ f. Bi (III) and S ______________

b. Ba and ClO31- _______________ g. K and Cl ______________

c. N(V) and O _______________ h. H and S ______________

d. Ca and PO43- _______________ i. Cr(III) and C2H3O21- ______________

e. Al and OH1- _______________ j. S (IV) and O ______________

Earlier in this chapter you determined the number of atoms found in the formulas of compounds.Problem 6 will help you to improve this skill and to better understand the meaning of chemical formulas. Ineach of the following problems indicate the total number of atoms in each formula. For example, the totalnumber of atoms in the formula H2O is three. In a formula which includes parentheses, such as Ca(NO3)2,the subscript to the right of the parentheses multiplies everything inside the parentheses. The totalnumber of atoms in Ca(NO3)2 is nine (1 Ca + 2 N + 6 O = 9). The formula Na2SO4 has seven atoms.

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Problem 6. Determine the total number of atoms contained in each of the following formulas.

a. NaCl __________ f. Pb(C2H3O2)2 __________

b. AlPO4 __________ g. Sr(NO3)2 __________

c. Fe(ClO3)3 __________ h. Ba3(PO4)2 __________

d. Ag2SO3 __________ i. Al(HCO3)3 __________

e. Na2Cr2O7 __________ j. (NH4)2CO3 __________

The formulas in Problem 7 below belong to a group of compounds known as "hydrates." They arecompounds that have water molecules included in them. The water is tacked on to the end of the formulafollowing a raised dot. The raised dot does NOT mean multiplication, as it might in algebra; rather, it means"plus." So, a formula such as BaCl2 •2H2O includes 2 water molecules. The total number of atoms in thisformula is nine (1 Ba, 2 Cl, 4 H, and 2 O). For each of the following hydrates, indicate the total number ofatoms in each formula.

Problem 7. For each of the following hydrates, indicate the total number of atoms in each formula.

a. CuSO4 •5H2O __________ b. Na2CO3 •10H2O __________ c. CoCl2 •6H2O ___________

SECTION 5.7 Rules For Naming Compounds

There are three methods for naming chemical compounds. They are the:

1. prefix method 2. Latin name method 3. Roman numeral method

Although there are some exceptions, generally speaking, these methods are used as follows.

The prefix method is most often used to name compounds which contain only nonmetals . Nonmetals arefound to the right of the "staircase" on the periodic table.

The Latin name method is used for compounds containing certain metals including iron (Fe), copper (Cu),tin (Sn), or mercury (Hg).

The Roman numeral method is used to name all compounds which contain metals. Metals are found tothe left of the "staircase" on the periodic table (excluding hydrogen).

A. The Prefix Method

You should MEMORIZE the following prefixes:

1 = mon or mono 4 = tetr or tetra 7 = hept or hepta2 = di 5 = pent or penta 8 = oct or octa3 = tri 6 = hex or hexa

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In this method prefixes are used to indicate the number of atoms of each element present in theformula of a compound. For example, As2O5 is called diarsenic pentoxide. Note that pent is used insteadof penta in order to avoid the awkward sound of the double vowel. If only one atom of the first element inthe formula is present the use of "mono" is usually avoided; if there is only one atom of the secondelement, then the prefix "mono" is always used. For example, SO2 is called sulfur dioxide (rather thanmonosulfur dioxide); however, the molecule CO is called carbon monoxide. Note that if the compound isbinary (contains only two elements), the name of the second element is changed so that it always endswith the suffix "ide". (Examples: sulfur dioxide and carbon monoxide.) Finish spelling the name on this

binary compound: CO2 is carbon diox_______. {3}

Problem 8. Name the following nonmetallic compounds using the prefix method.

a. SO3 _________________________ e. N2O ________________________

b. As2O3 _________________________ f. SF6 ________________________

c. PBr5 _________________________ g. CCl4 ________________________

d. SeF2 _________________________ h. NO ________________________

Caution: Some students confuse the use of Roman numerals in names with the use of prefixes in names.Here is the difference. Roman numerals indicate the oxidation number of an element. Prefixes indicatethe number of atoms of an element represented in the formula. For example, iron (III) oxide is Fe2O3.The Roman numeral (III) in the name tells us that the oxidation number of iron in this compound is +3. Itdoes NOT mean that there are three iron atoms represented in the formula. As you can see, there areonly two iron atoms represented. The compound N2O4 is called dinitrogen tetroxide. The "di" before thenitrogen means that there are two nitrogen atoms represented in the formula. The prefix does NOTindicate the oxidation number of the nitrogen.

B. The Latin Name Method

You need to MEMORIZE the Latin names for the elements listed in Table 5.4.

Note that the Latin name of the lower oxidation state of each element ends in "ous", while thename of the higher oxidation state ends in "ic". (You should refer to Table 5.2 for the possible oxidationstates of elements.) For example, the compound CuCl2 contains copper in the +2 oxidation state[copper(II)]. So, the Latin name of this compound is cupric chloride. On the other hand, CuCl containscopper in the +1 oxidation state. Its name is cuprous chloride. Therefore, in order to use this method ofnaming, you must first determine the oxidation state of the metal and then choose the proper Latin name.Note that if the compound contains only two elements, the name of the second element is changed sothat it always ends with the suffix "ide".

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Table 5.4 Latin Names of Four Selected Elements

Element Symbol Latin Name

copper (I) Cu1+ cuprouscopper (II) Cu2+ cupric

iron (II) Fe2+ ferrousiron (III) Fe3+ ferric

mercury (I) Hg1+ mercurousmercury (II) Hg2+ mercuric

tin (II) Sn2+ stannoustin (IV) Sn4+ stannic

(These Latin names can also be found in your Reference Notebook.)

In problem 9 you will be asked to assign Latin names to compounds. You must first determine theoxidation number of the metal in each compound. To do this, you should first determine the oxidationnumber of the other element present. Note the examples below.

Example 1: Let's find the Latin name for SnS2. According to Table 5.2, tin (Sn) has oxidation numbers of+2 and +4. But which of these is being used in the compound SnS2? Well, note from Table 5.2 that sulfur(S) can have oxidation numbers of -2, +4, or +6. Since the tin has only positive oxidation numbers, wemust use the negative oxidation number of the sulfur which is -2. Now, if sulfur is -2 here, and since thereare two atoms of sulfur in the formula, the total oxidation number of the sulfur in SnS2 is -4. Since the totalof the oxidation numbers in the formula must equal zero, the oxidation number of the single tin atom in theformula must be +4. When tin has an oxidation number of +4 its Latin name (see Table 5.4) is stannic.Thus, SnS2 is called stannic sulfide.

Example 2: What is the Latin name for Cu2O? Since oxygen is -2, the total oxidation number for thecopper (Cu) must be +2. Hey, but wait. There are two atoms of copper represented in the formula.Therefore, each individual copper atom must have an oxidation number of +1. Therefore, checking Table5.4, Cu2O is called cuprous oxide.

Problem 9. Name the following using the Latin name method. Calculate the oxidation number of themetal being used, then name the compound.

Ox. No. of Metal Name

a. SnS ____________ _________________________________________

b. HgCl ____________ _________________________________________

c. FeO ____________ _________________________________________

d. CuS ____________ _________________________________________

e. HgF2 ____________ _________________________________________

f. SnCl2 ____________ _________________________________________

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g. Fe2S3 ____________ _________________________________________

h. CuI ____________ _________________________________________

C. The Roman Numeral Method

When naming metallic compounds using this method, first determine the possible oxidationstates of the metal. If the metal has more than one positive oxidation state, then you must use a Romannumeral in the name. If the metal has only one positive oxidation state, then you should not use a Romannumeral in the name.

For example, let's try to name FeCl3 according to this method. Checking a reference sheetcontaining oxidation states we find that iron can have states of either +2 or +3. Therefore, we must use aRoman numeral in the name. The oxidation state of iron in FeCl3 is +3. The name of this compound is iron(III) chloride. Note that when a Roman numeral is used, it is the same number as the oxidation state of themetal. That is, if the oxidation state of iron in a compound is +3, then the Roman numeral used is (III).

Let's try another one. Name FeO. In FeO, the oxidation state of iron is +2. Therefore, the nameof FeO is iron (II) oxide. Note that the Roman numeral is always enclosed in parentheses. Let's name thecompound: BaCl2. The metal barium has only one positive oxidation state which is +2. Therefore, noRoman numeral is needed and the name is simply barium chloride. Note that if the compound containsonly two elements, the name of the second element is changed so that it always ends with the suffix "ide".

Problem 10. Name the following using the Roman numeral method. Use Roman numerals in the nameonly if needed. Check your list of oxidation numbers to see if a metal has more than one positive oxidationstate. If it does, use a Roman numeral in the name.

a. MnO2 ___________________________________

b. KBr ___________________________________

c. CrCl3 ___________________________________

d. HgS ___________________________________

e. FeBr2 ___________________________________

f. CaF2 ___________________________________

g. CrO3 ___________________________________

h. CuO ___________________________________

i. Al2O3 ___________________________________

j. Co2O3 ___________________________________

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D. Compounds Containing Polyatomic Ions

Polyatomic ions are charged particles which consist of more than one atom. Formulas which beginwith one of these ions are named by first naming the polyatomic ion, then naming the element whichfollows it and changing the ending by using the suffix "ide.". Examples include NH4Cl (ammoniumchloride) and (NH4)2S (ammonium sulfide). Formulas which end with one of these polyatomic ions arenamed by naming the first element and then naming the polyatomic ion. Example: CaSO4, calciumsulfate. A Roman numeral is added to the name only if a metal is involved that has more than one positiveoxidation number. For example, since copper can be +1 or +2, CuSO4 is called copper (II) sulfate.However, since aluminum can only be +3, Al(NO3)3 is simply called aluminum nitrate. Some formulasconsist of two polyatomic ions. They are named simply by naming the first polyatomic ion followed by thename of the second one. NH4NO3 is ammonium nitrate; (NH4)2SO3 is ammonium sulfite.

Do not use the prefix method when naming compounds containing polyatomic ions.

Problem 11. Name the following compounds which contain polyatomic ions.

a. Ca(C2H3O2)2 _____________________________________

b. Ba(NO2)2 _____________________________________

c. Fe(OH)2 _____________________________________ (2 names)

_____________________________________

d. (NH4)2O _____________________________________

e. Ag2SO4 _____________________________________

f. KMnO4 _____________________________________

g. CuCO3 _____________________________________ (2 names)

_____________________________________

h. NaHSO4 _____________________________________

i. NH4C2H3O2 _____________________________________

j. (NH4)3PO4 _____________________________________

Note: Do not mix the methods for naming compounds. For example, if we name FeCl2 ferrous (II) chloride,that is wrong because we mixed the Latin name method with the Roman numeral method. Wait! There isone exception to never mixing the methods. In hydrates (described below) you will notice that the Romannumeral and prefix methods are both used in a name.

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The compounds known as hydrates, which you studied earlier in this chapter, are named as follows:

CuSO4 •5H2O is called copper (II) sulfate pentahydrate. The prefix "penta" means "five", so pentahydratemeans "five waters," which is added to the name of the compound.

BaCl2 •2H2O is called barium chloride dihydrate. The prefix "di" means "two," so dihydrate means "twowaters." (You should MEMORIZE the prefixes for 1 through 8 which were listed on a previous page.)

Problem 12. Perform the following tasks dealing with hydrates.

a. Name this hydrate: CoCl2 •6H2O _____________________________________

b. Finish writing this formula for sodium sulfate heptahydrate: Na2SO4 • ______H2O

SECTION 5.8 Writing Correct Formulas From Names

Problem 13. Write correct formulas for the compounds named below. Use the table of oxidationnumbers in this chapter or in your reference notebook. Remember that the sum of the oxidation numbersof all the atoms and/or polyatomic ions in a formula must add up to zero.

a. calcium nitrate __________________ n. ammonium fluoride _________________

b. strontium chloride __________________ o. iron (III) sulfide _________________

c. phosphorus triiodide __________________ p. sodium carbonate _________________

d. silver phosphate __________________ q. carbon tetrachloride _________________

e. dinitrogen pentoxide __________________ r. cobalt (II) chloride _________________

f. stannous chlorate __________________ s. ferrous phosphate _________________

g. chromium (III) oxide __________________ t. lead (IV) oxide _________________

h. ammonium chromate __________________ u. antimony (V) sulfide _________________

i. cesium sulfite __________________ v. sulfur hexabromide _________________

j. strontium fluoride __________________ w. silver oxide _________________

k. hydrogen iodide __________________ x. manganese (IV) chloride _____________

l. iron (III) chloride hexahydrate __________________________

m. calcium sulfate dihydrate __________________________

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SECTION 5.9 More Practice With Naming Compounds

Problem 14. Name the compounds below. Before deciding upon a name, first check to see if thecompound contains a metal. Use the prefix method for compounds that do not contain a metal; use theRoman numeral method for compounds that do contain a metal. (Metals are found to the left of the"staircase" on the periodic table.) Remember you should not mix the three methods of naming.

Formula Name a. CaCl2 _______________________________________________

b. Al2S3 _______________________________________________

c. Ba(OH)2 _______________________________________________

d. CaCO3 _______________________________________________

e. MgSO3 _______________________________________________

f. Pb3(PO4)2 _______________________________________________

g. As2O5 _______________________________________________

h. PBr3 _______________________________________________

i. KOH _______________________________________________

j. AsCl5 _______________________________________________

k. Ag2S _______________________________________________

l. SrCr2O7 _______________________________________________

m. CsHSO4 _______________________________________________

n. Co(NO2)2 _______________________________________________

o. SrSO4 _______________________________________________

p. NaHCO3 _______________________________________________

q. MgO _______________________________________________

r. CrF3 _______________________________________________

s. (NH4)2Cr2O7 _______________________________________________

t. Ni(ClO3)2 _______________________________________________

u. CBr4 _______________________________________________

v. Na3PO4 _______________________________________________

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w. N2O3 _______________________________________________

x. Pb(C2H3O2)2_______________________________________________

y. P2O5 _______________________________________________

z. KCN _______________________________________________

aa. LiNO3 _______________________________________________

bb. Na2CrO4 _______________________________________________

Problem 15. Give two names for each of the following. Put the Latin name in the left column and theRoman numeral name in the right column.

Latin Name Roman Numeral Name

a. HgBr _______________________________ ______________________________

b. Fe(OH)2 _______________________________ ______________________________

c. HgCl2 _______________________________ ______________________________

d. Fe2(SO4)3 _______________________________ ______________________________

e. Cu2S _______________________________ ______________________________

f. SnCrO4 _______________________________ ______________________________

g. Cu(OH)2 _______________________________ ______________________________

h. HgNO3 _______________________________ ______________________________

i. SnO2 _______________________________ ______________________________

SECTION 5.10 A Summary Of Things To Memorize

1. Symbols of selected elements (Table 5.1)

2. Names, symbols and charges of polyatomic ions (Table 5.3)

3. Selected Latin names of elements (Table 5.4)

4. Selected Greek prefixes for the numbers 1 through 8.

It will also be assumed that you can recognize and write Roman numerals for at least the first eightnumbers: I, II, III, IV, V, VI, VII, VIII

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SECTION 5.11 Learning Outcomes

You are now at the end of chapter 5. Check the learning outcomes below. When you feel thatyou have mastered all of them, arrange to take any test or quizzes on chapter 5, and then go to Chapter 6.

_____1. Distinguish between elements, compounds, heterogeneous mixtures, homogeneous mixtures, and pure substances.

_____2. Distinguish between atoms, molecules, and ions.

_____3. Write from memory the names (spelled correctly) and symbols of selected common elements.

_____4. Be able to identify the four important ideas which composed Dalton's Atomic Theory.

_____5. Write from memory the Latin names (spelled correctly) for the lower and higher oxidation states of copper, iron, mercury, and tin.

_____6. Write from memory the names (spelled correctly), formulas, and charges of the common polyatomic ions.

_____7. Name compounds using the Roman numeral method.

_____8. Name compounds using the Latin name method.

_____9. Name compounds using the prefix method.

_____10. Name compounds which are hydrates.

_____11. Calculate the number of atoms in the formulas of compounds (including hydrates).

_____12. Use oxidation numbers to write correct formulas for compounds given their names or the elements they contain.

_____13. Write from memory the common Greek prefixes.

_____14. Write from memory the names and symbols of common elements.

5-20 ©1997, A.J. Girondi

SECTION 5.12 Answers to Questions and Problems

Questions:

{1} No; {2} Magnet is attracted to pure iron, but not attracted to iron when it is in a compound;{3} ide

Problems:

1. 1,1,42. 1,2,3,23. a. BaCl2; b. HgBr; c. CaO; d. HgCl2; e. Al2S3; f. Ag2S; g. N2O3; h. Na2O; i. Cu2S;

j. As2O5; k. CO2; l. SnBr4; m. PI3 ; n. AsCl5; o. SnF2; p. SrBr24. a. MgSO4; b. SnCrO4; c. NaHCO3 d. Fe(OH)2; e. Pb3(PO4)2; f. NH4Cl; g. Al2(SO3)3;

h. ZnCO3; i. Cu(OH)2; j. Fe2(SO4)3; k. HgNO3; l. (NH4)2Cr2O7

5. a. MgF2; b. Ba(ClO3)2; c. N2O5; d. Ca3(PO4)2; e. Al(OH)3; f. Bi2S3 g. KCl; h. H2S; i. Cr(C2H3O2)3j. SO2

6. a. 2; b. 6; c. 13; d. 6; e. 11; f. 15; g. 9; h. 13; i. 16; j. 147. a. 21; b. 36; c. 218. a. sulfur trioxide; b. diarsenic trioxide; c. phosphorus pentabromide; d. selenium difluoride;

e. dinitrogen monoxide; f. sulfur hexafluoride; g. carbon tetrachloride; h. nitrogen monoxide9. a. +2, stannous sulfide; b. +1, mercurous chloride; c. +2, ferrous oxide; d. +2, cupric sulfide

e. +2, mercuric fluoride; f. +2, stannous chloride; g. +3, ferric sulfide; h. +1, cuprous iodide10. a. manganese (IV) oxide; b. potassium bromide; c. chromium (III) chloride

d. mercury (II) sulfide; e. iron (II) bromide; f. calcium fluoride; g. chromium (VI) oxide;h. copper (II) oxide; i. aluminum oxide; j. cobalt (III) oxide

11. a. calcium acetate; b. barium nitrite; c. iron (II) hydroxide, ferrous hydroxide;d. ammonium oxide; e. silver sulfate; f. potassium permanganate;g. copper (II) carbonate, cupric carbonate; h. sodium hydrogen sulfate; i. ammonium acetate;j. ammonium phosphate

12. a. cobalt (II) chloride hexahydrate; b. Na2SO4 • 7 H2O13. a. Ca(NO3)2; b. SrCl2; c. PI3; d. Ag3PO4; e. N2O5; f. Sn(ClO3)2; g. Cr2O3; h. (NH4)2CrO4;

i. Cs2SO3; j. SrF2; k. HI; l. FeCl3 • 6 H2O; m. CaSO4 • 2 H2O; n. NH4F; o. Fe2S3; p. Na2CO3;q. CCl4; r. CoCl2; s. Fe3(PO4)2; t. PbO2; u. Sb2S5; v. SBr6; w. Ag2O; x. MnCl4

14. a. calcium chloride; b. aluminum sulfide; c. barium hydroxide; d. calcium carbonate;e. magnesium sulfite; f. lead (II) phosphate; g. diarsenic pentoxide; h. phosphorus tribromide;i. potassium hydroxide; j. arsenic pentachloride; k. silver sulfide; l. strontium dichromate;m. cesium hydrogen sulfate; n. cobalt (II) nitrite; o.strontium sulfate; p. sodium hydrogen carbonate;q. magnesium oxide; r. chromium (III) fluoride; s. ammonium dichromate; t. nickel chlorate;u. carbon tetrabromide; v. sodium phosphate; w. dinitrogen trioxide; x. lead (II) acetate;y. diphosphorus pentoxide; z. potassium cyanide; aa. lithium nitrate; bb. sodium chromate

15. a. mercurous bromide, mercury (I) bromideb. ferrous hydroxide, iron (II) hydroxidec. mercuric chloride, mercury (II) chlorided. ferric sulfate, iron (III) sulfatee. cuprous sulfide, copper (I) sulfidef. stannous chromate, tin (II) chromateg. cupric hydroxide, copper (II) hydroxideh. mercurous nitrate, mercury (I) nitratei. stannic oxide, tin (IV) oxide

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SECTION 5.13 Student Notes

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