Chemical Formulas and Chemical Compounds

Chemical Formulas and Chemical Chemical Formulas and Chemical CompoundsCompounds

Chapter 7Chapter 7

Chemical FormulasChemical Formulas

• Combinations of symbols are used to represent Combinations of symbols are used to represent compounds of two or more elements.compounds of two or more elements.

• Also indicate the ratio of the number of atoms Also indicate the ratio of the number of atoms of each type of element in the compound.of each type of element in the compound.• HH22O – means that there are 2 hydrogen atoms for O – means that there are 2 hydrogen atoms for

every oxygen atom.every oxygen atom.• No subscript on O – means there is 1No subscript on O – means there is 1

Chemical FormulasChemical Formulas

• Show either one molecule or one formula Show either one molecule or one formula unitunit

Organic CompoundsOrganic Compounds

• Written differently than other formulasWritten differently than other formulas• The shorthand shows how the atoms are The shorthand shows how the atoms are

joined, not just the number present.joined, not just the number present.• Example – Example –

• CHCH33COOH, not CCOOH, not C22HH44OO22

IonsIons

• Ion – charged atom or group of atomsIon – charged atom or group of atoms• Monatomic Ions – single atomMonatomic Ions – single atom• Polyatomic Ions – more than one atomPolyatomic Ions – more than one atom

Monatomic IonsMonatomic Ions

• Can be anions or cationsCan be anions or cations• Transition elements can form more than one Transition elements can form more than one

kind of ionkind of ion• See table 7-1 on page 205See table 7-1 on page 205• You must memorize this table.You must memorize this table.

Naming monatomic ionsNaming monatomic ions

• CationsCations• Element’s nameElement’s name• Roman numerals are used when there are Roman numerals are used when there are

multiple ionsmultiple ions

• AnionsAnions• Drop the element name endingDrop the element name ending• Add -ideAdd -ide

Binary compoundsBinary compounds

• Contain two different elementsContain two different elements• When we write chemical formula for a When we write chemical formula for a

compound, the charges must add up to zero.compound, the charges must add up to zero.• Write the positive ion first.Write the positive ion first.

ExampleExample

• Write a formula for a compound of tin (II) Write a formula for a compound of tin (II) and Iodine.and Iodine.

• Tin (II) is 2+Tin (II) is 2+• Iodine is 1-Iodine is 1-• We need two iodines to cancel out the We need two iodines to cancel out the

charge on the tin (II).charge on the tin (II).• SnISnI22

NomenclatureNomenclature

• Naming systemNaming system• Works for most compoundsWorks for most compounds

Naming binary compoundsNaming binary compounds

• Write the name of the positive cation first.Write the name of the positive cation first.• Add the name of the negative anionAdd the name of the negative anion

• AlN – Aluminum nitrideAlN – Aluminum nitride• KCl – potassium chlorideKCl – potassium chloride

The stock systemThe stock system

• Elements with more than one possible Elements with more than one possible chargecharge

• CuCu22S – copper (I) sulfideS – copper (I) sulfide

• CuS – copper (II) sulfideCuS – copper (II) sulfide• Note – in an older naming system the above Note – in an older naming system the above

could be written as cuprous sulfide and could be written as cuprous sulfide and cupric sulfidecupric sulfide

OxyanionsOxyanions

• Polyatomic ions that contain oxygenPolyatomic ions that contain oxygen• When there are two or more oxyanions When there are two or more oxyanions

formed from the same two elements, the formed from the same two elements, the most common has the ending –atemost common has the ending –ate• The ion with one less oxygen than –ate ends in The ion with one less oxygen than –ate ends in

–ite–ite• The ion with one less oxygen than –ite adds the The ion with one less oxygen than –ite adds the

prefix hypo-prefix hypo-• The ion with one more oxygen than –ate adds The ion with one more oxygen than –ate adds

the prefix per-the prefix per-

Compounds with polyatomic Compounds with polyatomic ionsions

• See table 7-2 on page 210See table 7-2 on page 210• They are written like binary compounds.They are written like binary compounds.

• Except the ending isn’t changed to end in –ideExcept the ending isn’t changed to end in –ide

• CuSOCuSO44 – copper (II) sulfate – copper (II) sulfate

• Sn(SOSn(SO44))22 – tin (IV) sulfate – tin (IV) sulfate

DiscussDiscuss

• Practice problems 7-1, 7-2, and 7-3 on Practice problems 7-1, 7-2, and 7-3 on pages 207, 209, and 211pages 207, 209, and 211

• PracticePractice

Polyatomic ions you must memorizePolyatomic ions you must memorize

• AmmoniumAmmonium• AcetateAcetate• ChlorateChlorate• ChloriteChlorite• HydroxideHydroxide• HypochloriteHypochlorite• NitrateNitrate• NitriteNitrite

• PerchloratePerchlorate• PermanganatePermanganate• CarbonateCarbonate• PeroxidePeroxide• SulfateSulfate• SulfiteSulfite• PhosphatePhosphate

Naming binary molecular Naming binary molecular compoundscompounds

• Two systems – one will be covered in section Two systems – one will be covered in section 7-27-2

• Older systemOlder system• Prefixes used – see table 7-3 on page 212Prefixes used – see table 7-3 on page 212

• CO – carbon monoxideCO – carbon monoxide

• COCO22 – carbon dioxide – carbon dioxide

• SOSO22 – sulfur dioxide – sulfur dioxide

• SOSO33 sulfur trioxide sulfur trioxide

RulesRules

• List the less-electronegative element first.List the less-electronegative element first.• Only has a prefix if there is more than one.Only has a prefix if there is more than one.

• The second elementThe second element• Has a prefixHas a prefix

• Root of the element nameRoot of the element name

• -ide ending-ide ending

• If the word begins with a vowel, drop the If the word begins with a vowel, drop the oo or or aa at at the end of the prefix (monoxide, not monooxide)the end of the prefix (monoxide, not monooxide)

• Order: C, P, N, H, S, I, Br, Cl, O, FOrder: C, P, N, H, S, I, Br, Cl, O, F

ExamplesExamples

• PFPF55

• Phosphorus pentafluoridePhosphorus pentafluoride

• NN22OO55

• Dinitrogen pentoxideDinitrogen pentoxide

• OFOF22

• Oxygen difluorideOxygen difluoride

AcidsAcids

• Have a different naming rules.Have a different naming rules.• Some common ones are listed in table 7-5 Some common ones are listed in table 7-5

on page 214on page 214• You should knowYou should know

• Hydrochloric acid (HCl)Hydrochloric acid (HCl)

• Sulfuric acid (HSulfuric acid (H22SOSO44))

• Acetic acid (CHAcetic acid (CH33COOH) (vinegar)COOH) (vinegar)

SaltsSalts

• An ionic compound composed of a cation An ionic compound composed of a cation and the anion from an acidand the anion from an acid

• Sometimes the salt keeps one or more Sometimes the salt keeps one or more hydrogen atoms from the acidhydrogen atoms from the acid• The prefix bi- or the word hydrogen is added to The prefix bi- or the word hydrogen is added to

the anion namethe anion name• HCOHCO33

--

• Hydrogen carbonate ion or bicarbonate ionHydrogen carbonate ion or bicarbonate ion

DiscussDiscuss

• Sample problem 7-4 on page 213Sample problem 7-4 on page 213• PracticePractice

DiscussDiscuss

• www.dhmo.org/facts.htmlwww.dhmo.org/facts.html

Oxidation numbersOxidation numbers

• Also called oxidation statesAlso called oxidation states• Assigned to atoms in moleculesAssigned to atoms in molecules• Indicate the general distribution of electrons Indicate the general distribution of electrons

among the bonded atomsamong the bonded atoms• Sort of like ionic chargeSort of like ionic charge

Pure elementsPure elements

• Have oxidation numbers of zeroHave oxidation numbers of zero• Single atoms – NaSingle atoms – Na• Molecules of a pure substanceMolecules of a pure substance

• OO22

• PP44

• SS88

Like charges on ionsLike charges on ions

• Shared electrons are assumed to belong to Shared electrons are assumed to belong to the more-electronegative atomthe more-electronegative atom

• The more electronegative element gets a The more electronegative element gets a number equal to the negative charge it number equal to the negative charge it would have as an anion.would have as an anion.

• The less electronegative element gets a The less electronegative element gets a number equal to the positive charge it number equal to the positive charge it would have as a cation.would have as a cation.

FluorineFluorine

• Oxidation number of -1Oxidation number of -1• The most electronegative elementThe most electronegative element

OxygenOxygen

• Usually -2Usually -2• In peroxides, -1In peroxides, -1

• HH22OO22

• In compounds with halogens, +2In compounds with halogens, +2• OFOF22

HydrogenHydrogen

• +1 with more electronegative elements+1 with more electronegative elements• -1 with metals-1 with metals

Sum of oxidation numbersSum of oxidation numbers

• In a neutral compound must be zeroIn a neutral compound must be zero• In a polyatomic ion must equal the charge In a polyatomic ion must equal the charge

on the ionon the ion

IonIon

• Can be assigned an oxidation number equal Can be assigned an oxidation number equal to the charge on the ionto the charge on the ion

ExampleExample

• Assign oxidation numbers to each atom in Assign oxidation numbers to each atom in the following compound:the following compound:

• KClOKClO44

• O is -2, which gives -8, since there are 4.O is -2, which gives -8, since there are 4.• The charge on perchlorate is 1-, so Cl must be The charge on perchlorate is 1-, so Cl must be

+7+7• K must be +1 to cancel out the 1-K must be +1 to cancel out the 1-

• +1, +7, -2+1, +7, -2

ExampleExample


• SOSO332-2-

• O is -2, which gives -6, since there are 3.O is -2, which gives -6, since there are 3.• The charge on sulfite is 2-, so S must be +4The charge on sulfite is 2-, so S must be +4

• +4, -2+4, -2

You tryYou try


• COCO22

• O is -2, which gives -4, since there are 2.O is -2, which gives -4, since there are 2.• The charge is 0, so C must be +4The charge is 0, so C must be +4

• +4, -2+4, -2

You tryYou try


• NONO33--

• O is -2, which gives -6, since there are 3.O is -2, which gives -6, since there are 3.• The charge is 1-, so N must be +5The charge is 1-, so N must be +5

• +5, -2+5, -2

More oxidation numbersMore oxidation numbers

• See Appendix Table A-15See Appendix Table A-15• There is also a pattern on the periodic tableThere is also a pattern on the periodic table• Group 1 is usually +1Group 1 is usually +1• Group 2 is usually +2Group 2 is usually +2• Group 13 is usually +3Group 13 is usually +3• Group 14 is usually +2 or +4Group 14 is usually +2 or +4• Group 15 is usually -3Group 15 is usually -3• Group 16 is usually -2Group 16 is usually -2• Group 17 is usually -1Group 17 is usually -1

The stock systemThe stock system

• Can be used instead of prefixes for molecular Can be used instead of prefixes for molecular compoundscompounds

• Use the oxidation numberUse the oxidation number• SOSO22

• Sulfur dioxideSulfur dioxide• Sulfur (IV) oxideSulfur (IV) oxide

• SOSO33

• Sulfur trioxideSulfur trioxide• Sulfur (VI) oxideSulfur (VI) oxide

DiscussDiscuss

• Name each of the following binary Name each of the following binary molecular compounds according to the molecular compounds according to the stock systemstock system

• CICI44

• SOSO33

• AsAs22SS33

• NClNCl33

Formula massFormula mass

• The sum of the average atomic masses of The sum of the average atomic masses of all the atoms in a formulaall the atoms in a formula

• For ions or moleculesFor ions or molecules• Can also be called molecular mass for Can also be called molecular mass for

moleculesmolecules

ExampleExample

• Find the formula mass of NaFind the formula mass of Na22SOSO33

• 126.05 amu126.05 amu

ExampleExample

• Find the formula mass of HClOFind the formula mass of HClO33

• 84.46 amu84.46 amu

You tryYou try

• Find the formula mass of MnOFind the formula mass of MnO44--

• 118.94 amu118.94 amu

You tryYou try

• Find the formula mass of CFind the formula mass of C22HH66OO

• 46.08 amu46.08 amu

Molar MassMolar Mass

• Chapter 3Chapter 3• The mass in grams of one mole (6.022 x The mass in grams of one mole (6.022 x

10102323 particles) of a substance particles) of a substance• Example: HExample: H22OO

• The mass of two moles of hydrogen atoms and The mass of two moles of hydrogen atoms and one mole of oxygen atomsone mole of oxygen atoms

ExampleExample

• Find the molar mass of KFind the molar mass of K22SOSO44

• 174.27 g/mol174.27 g/mol

You tryYou try

• Find the molar mass of (NHFind the molar mass of (NH44))22CrOCrO44

• 152.10 g/mol152.10 g/mol

Formula mass and molar massFormula mass and molar mass

• Numerically equalNumerically equal• Only the units are differentOnly the units are different

DiscussDiscuss

• How many moles of atoms of each element How many moles of atoms of each element are there in one mole of ammonium are there in one mole of ammonium carbonate, (NHcarbonate, (NH44))22COCO33

• 2 mol N, 8 mol H, 1 mol C, 3 mol O2 mol N, 8 mol H, 1 mol C, 3 mol O

• Determine both the formula mass and the Determine both the formula mass and the molar mass of ammonium carbonatemolar mass of ammonium carbonate• 96.11 amu, 96.11 g/mol96.11 amu, 96.11 g/mol

Converting with molar massConverting with molar mass

• Relate mass in grams to number of molesRelate mass in grams to number of moles• Relate mass in grams to number of particlesRelate mass in grams to number of particles

ExampleExample

• What is the mass in grams of 3.04 mol of What is the mass in grams of 3.04 mol of ammonia vapor, NHammonia vapor, NH33??

• 51.8 g51.8 g

You tryYou try

• What is the mass in grams of 0.257 mol of What is the mass in grams of 0.257 mol of calcium nitrate, Ca(NOcalcium nitrate, Ca(NO33))22??

• 42.2 g42.2 g

ExampleExample

• How many moles of SOHow many moles of SO22 are in 3.82 g? are in 3.82 g?

• 0.0596 mol0.0596 mol

You tryYou try

• How many moles of ClHow many moles of Cl22 are there in 77.1 g? are there in 77.1 g?

• 1.09 mol1.09 mol

ExampleExample

• How many molecules are there in 77.1 g How many molecules are there in 77.1 g ClCl22??

• 6.55 x 106.55 x 102323 molecules molecules

You tryYou try

• How many molecules are in 4.15 x 10How many molecules are in 4.15 x 10 -3-3 g of g of CC66HH1212OO66??

• 1.39 x 101.39 x 101919 molecules molecules

Percentage compositionPercentage composition

• Percentage by mass of each element in a Percentage by mass of each element in a compoundcompound

• Example: gumExample: gum

ExampleExample

• Find the percentage composition of sodium Find the percentage composition of sodium nitrate NaNOnitrate NaNO33..

• 27.05% Na27.05% Na• 16.48% N16.48% N• 56.47% O56.47% O

You tryYou try

• Find the percentage composition of silver Find the percentage composition of silver sulfate, Agsulfate, Ag22SOSO44..

• 69.19% Ag69.19% Ag• 10.29% S10.29% S• 20.53% O20.53% O

DiscussDiscuss

• Zinc chloride, ZnClZinc chloride, ZnCl22 is 52.02% chlorine by is 52.02% chlorine by

mass. What mass of chlorine is contained mass. What mass of chlorine is contained in 80.3 g of ZnClin 80.3 g of ZnCl22??

• How many moles of Cl is this?How many moles of Cl is this?• 41.8 g41.8 g• 1.18 mol1.18 mol

Empirical formulaEmpirical formula

• The symbols for the elements combined in a The symbols for the elements combined in a compoundcompound

• Subscripts show the smallest whole-number Subscripts show the smallest whole-number mole ratio of the atomsmole ratio of the atoms

• Determined from the percent composition Determined from the percent composition of a substanceof a substance

Empirical formulaEmpirical formula

• Usually the same as an ion’s formula unitUsually the same as an ion’s formula unit• Not always the same as the molecular Not always the same as the molecular

formulaformula• Diborane’s molecular formula is BDiborane’s molecular formula is B22HH66

• The empirical formula is BHThe empirical formula is BH33

ExampleExample

• A compound is analyzed and found to A compound is analyzed and found to contain 36.70% potassium, 33.27% contain 36.70% potassium, 33.27% chlorine, and 30.03% oxygen. What is the chlorine, and 30.03% oxygen. What is the empirical formula of the compound?empirical formula of the compound?

• KClOKClO22

You tryYou try

• Determine the empirical formula of the Determine the empirical formula of the compound that contains 17.15% carbon, compound that contains 17.15% carbon, 1.44% hydrogen, and 81.41% fluorine.1.44% hydrogen, and 81.41% fluorine.

• CHFCHF33

ExampleExample

• A 60.0 g sample of tetraethylead, a gasoline A 60.0 g sample of tetraethylead, a gasoline additive, is found to contain 38.43 g lead, additive, is found to contain 38.43 g lead, 17.83 g carbon, and 3.74 g hydrogen. Find 17.83 g carbon, and 3.74 g hydrogen. Find its empirical formulaits empirical formula

• PbCPbC88HH2020

You tryYou try

• A 170.00 g sample of an unidentified A 170.00 g sample of an unidentified compound contains 29.84 g sodium, 67.49 g compound contains 29.84 g sodium, 67.49 g chromium, and 72.67 g oxygen. What is its chromium, and 72.67 g oxygen. What is its empirical formula?empirical formula?

• NaNa22CrCr22OO77

DiscussDiscuss

• Find the empirical formula of a compound Find the empirical formula of a compound that contains 53.70% iron and 46.30% that contains 53.70% iron and 46.30% sulfur.sulfur.

• FeFe22SS33

Molecular formulaMolecular formula

• Show how many atoms are in each Show how many atoms are in each moleculemolecule

• Related to empirical formulaRelated to empirical formula

• x is the whole number the subscripts must x is the whole number the subscripts must be multiplied bybe multiplied by• It might be 1It might be 1

formulamolecular formula empirical x

Mass relationshipMass relationship

mass formulamolecular mass formula empirical x

ExampleExample

• The empirical formula for The empirical formula for trichloroisocyanuric acid is OCNCl. The trichloroisocyanuric acid is OCNCl. The molar mass of this compound is 232.41 molar mass of this compound is 232.41 g/mol. What is its molecular formula?g/mol. What is its molecular formula?

• OO33CC33NN33ClCl33

ExampleExample

• Determine the molecular formula of a Determine the molecular formula of a compound with an empirical formula of compound with an empirical formula of NHNH22 and a formula mass of 32.06 amu. and a formula mass of 32.06 amu.

• NN22HH44

You tryYou try

• Determine the molecular formula of the Determine the molecular formula of the compound with an empirical formula of CH compound with an empirical formula of CH and a formula mass of 78.110 amu.and a formula mass of 78.110 amu.

• CC66HH66

ExampleExample

• If 4.04 g of N combine with 11.46 g of O to If 4.04 g of N combine with 11.46 g of O to produce a compound with a formula mass produce a compound with a formula mass of 108.0 amu, what is the molecular of 108.0 amu, what is the molecular formula of this compound?formula of this compound?

• NN22OO55

You tryYou try

• The molar mass of a compound is 92 g/mol. The molar mass of a compound is 92 g/mol. Analysis of a sample of the compound Analysis of a sample of the compound indicates that it contains 0.606 g N and indicates that it contains 0.606 g N and 1.390 g O. Find its molecular formula.1.390 g O. Find its molecular formula.

• NN22OO44

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Chemical Formulas and Chemical Compounds