Chapter 5 Molecules and Compounds

Tro's "Introductory Chemistry", Chapter 5 2 Molecules and Compounds When elements combine to form compounds their properties change Salt Sodium—shiny, reactive, poisonous. Chlorine—pale yellow gas, reactive, poisonous. Sodium chloride—table salt. Sugar Carbon—pencil or diamonds. Hydrogen—flammable gas. Oxygen—a gas in air. Combine to form white crystalline sugar.

Tro's "Introductory Chemistry", Chapter 5 3 Compounds Display Constant Composition All pure substances have constant composition. All samples of a pure substance contain the same elements in the same percentages (ratios). Mixtures have variable composition.

Tro's "Introductory Chemistry", Chapter 5 4 Example: Constant Composition If we decompose water, we find 16.0 grams of oxygen to every 2.00 grams of hydrogen. Water has a constant mass ratio of oxygen to hydrogen of 8.0.

Tro's "Introductory Chemistry", Chapter 5 5 How to Represent Compounds A compound is substance that is composed of atoms of two or more elements. Compounds can be represented Writing the symbol of each element present in the compound. describing the number of each atom in the simplest unit of the compound. The number of atoms of each element is written to the right of the element as a subscript. If there is only one atom, the 1 subscript is not written. Polyatomic groups are placed in parentheses. If more than one.

Tro's "Introductory Chemistry", Chapter 5 6 Water = H 2 O  two atoms of hydrogen and 1 atom of oxygen Table sugar = C 12 H 22 O 11  12 atoms of C, 22 atoms of H and 11 atoms O How to Represent Compounds

Tro's "Introductory Chemistry", Chapter 5 7 Order of Elements in a Formula Metals are written first. NaCl Nonmetals are written in order from Table 5.1. CO 2 There are occasional exceptions for historical or informational reasons.  H 2 O, but NaOH. Table 5.1 Order of Listing Nonmetals in Chemical Formulas CPNHSIBrClOF

Tro's "Introductory Chemistry", Chapter 5 8 Example—Write Formulas for Each of the Following Compounds. Hematite—Composed of four oxide ions for every three iron ions. Acetone—Each molecule contains six hydrogen atoms, three carbon atoms, and one oxygen atom. Fe 3 O 4 C3H6OC3H6O

Tro's "Introductory Chemistry", Chapter 5 9 Molecules with Polyatomic Ions Mg(NO 3 ) 2 Compound called magnesium nitrate. Symbol of the polyatomic ion called nitrate. Symbol of the polyatomic ion called sulfate. CaSO 4 Compound called calcium sulfate. Implied “1” subscript on magnesium. Implied “1” subscript on calcium. Parentheses to group two NO 3 s.No parentheses for one SO 4.

10 Molecules with Polyatomic Ions, Continued Mg(NO 3 ) 2 Compound called magnesium nitrate. CaSO 4 Compound called calcium sulfate. Subscript indicating two NO 3 groups. No subscript indicating one SO 4 group. Implied “1” subscript on nitrogen, total 2 N. Implied “1” subscript on sulfur, total 1 S. Stated “3” subscript on oxygen, total 6 O. Stated “4” subscript on oxygen, total 4 O.

Tro's "Introductory Chemistry", Chapter 5 11 Example—Determine the Total Number of Atoms or Ions in One Formula Unit of Each of the Following. Mg(C 2 H 3 O 2 ) 2 Practice (Hg 2 ) 3 (PO 4 ) 2 1 Mg + 4 C + 6 H + 4 O = 15

Tro's "Introductory Chemistry", Chapter 5 12 Classifying Materials Atomic elements = Elements whose particles are single atoms. Molecular elements = Elements whose particles are multi-atom molecules. Molecular compounds = Compounds whose particles are molecules made of only nonmetals. Ionic compounds = Compounds whose particles are cations and anions.

13 Molecular Elements Certain elements occur as diatomic molecules. i.e., two atoms of the same element bonded together H2H2 Cl 2 Br 2 I2I2 7 7A N 2 O 2 F 2

Tro's "Introductory Chemistry", Chapter 5 14 Molecular Compounds Two or more nonmetals. Smallest unit is a molecule.

Tro's "Introductory Chemistry", Chapter 5 15 Ionic Compounds Metals + nonmetals. No individual molecule units, instead have a 3-dimensional array of cations and anions made of formula units.

16 Molecular View of Elements and Compounds

Tro's "Introductory Chemistry", Chapter 5 17 Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or Ionic Compound, Continued. Aluminum, Al Aluminum chloride, AlCl 3 Chlorine, Cl 2 Acetone, C 3 H 6 O Carbon monoxide, CO Cobalt, Co = Atomic element. = Ionic compound. = Molecular element. = Molecular compound. = Atomic element

Tro's "Introductory Chemistry", Chapter 5 18 Ionic Compounds Ionic compounds are made of ions. Ionic compounds always contain cations and anions. Cations = + charged ions; anions = − charged ions. The sum of the + charges of the cations must equal the sum of the − charges of the anions. If Na + is combined with S 2-, you will need 2 Na + ions for every S 2- ion to balance the charges, therefore the formula must be Na 2 S.

Tro's "Introductory Chemistry", Chapter 5 19 Writing Formulas for Ionic Compounds NAME-TO-FORMULA 1.Write the symbol for the metal cation and its charge. 2.Write the symbol for the nonmetal anion and its charge. 3.Charge (without sign) becomes subscript for the other ion. 4.Reduce subscripts to smallest whole-number ratio. 5.Check that the sum of the charges of the cation cancels the sum of the anions.

Tro's "Introductory Chemistry", Chapter 5 20 Write the Formula of a Compound Made from Aluminum Ions and Oxide Ions. 1.Write the symbol for the metal cation and its charge. 2.Write the symbol for the nonmetal anion and its charge. 3.Charge (without sign) becomes subscript for the other ion. 4.Reduce subscripts to smallest whole-number ratio. 5.Check that the total charge of the cations cancels the total charge of the anions. Al +3 column 3A O 2- column 6A Al +3 O 2- Al 2 O 3 Al = (2)∙(+3) = +6 O = (3)∙(-2) = -6

Tro's "Introductory Chemistry", Chapter 5 21 Practice—What Are the Formulas for Compounds Made from the Following Ions? Potassium ion with a nitride ion. Calcium ion with a bromide ion. Aluminum ion with a sulfide ion.

Tro's "Introductory Chemistry", Chapter 5 22 Metal Cations 22 TYPE 1 Main group metals have invariant charge i.e., metals whose ions can have only one possible charge  Groups 1A & 2A, Al 3+, Ag 1+, Zn 2+, Sc 3+ cation name = metal name

Tro's "Introductory Chemistry", Chapter 5 23 Metal Cations 23 TYPE 2 Transition metals  metals with variable charges i.e., metals whose ions can have more than one possible charge  determine charge of cation by charge on anion  name = metal name with Roman numeral charge in parentheses

Tro's "Introductory Chemistry", Chapter 5 24 Naming Monatomic Nonmetal Anion Determine the charge from position on the Periodic Table. To name anion, change ending on the element name to -ide. 4A = 4−5A = 3−6A = 2−7A = 1− C = carbideN = nitrideO = oxideF = fluoride Si = silicideP = phosphideS = sulfideCl = chloride

Tro's "Introductory Chemistry", Chapter 5 25 Naming Ionic Compounds FORMULA-TO-NAME Recall: ionic compounds are made of cations and anions Name the cation first, followed by the anion if cation is:  main group metal = metal name  transition metal = metal name(charge)  polyatomic ion = name of polyatomic ion if anion is:  nonmetal = stem of nonmetal name + -ide  polyatomic ion = name of polyatomic ion

Tro's "Introductory Chemistry", Chapter ) Naming binary Ionic Compounds for Metals with Invariant Charge 2) Naming Binary Ionic Compounds for Metals with Variable Charge Summary Summary Summary

Tro's "Introductory Chemistry", Chapter 5 27 Example : What is the name of the compound CsF 27 1.Identify cation and anion. Cs = Cs + because it is in Group 1A F = F – because it is in Group 7A 2.Name the cation. Cs + = cesium 3.Name the anion. F – = fluoride 4.Write the cation name first, then the anion name. cesium fluoride

Tro's "Introductory Chemistry", Chapter 5 28 Practice: Name the following compounds 28 1.KCl 2.MgBr 2

Tro's "Introductory Chemistry", Chapter 5 29 Determining the Charge on a Cation with Variable Charge e.g., Au 2 S 3 1.Determine the charge on the anion Au 2 S 3 —The anion is S. Since it is in Group 6A, its charge is 2− 2.Determine the total negative charge Since there are 3 S in the formula, the total negative charge is −6 3.Determine the total positive charge Since the total negative charge is −6, the total positive charge is +6 4.Divide by the number of cations Since there are 2 Au in the formula and the total positive charge is +6, each Au has a 3+ charge

Tro's "Introductory Chemistry", Chapter 5 30 Practice : Find the charge on the cation. 30 CrO 3 Fe 3 N 2

Tro's "Introductory Chemistry", Chapter 5 31 Example: Naming Binary Ionic with Variable Charge Metal CuF 2 1.Identify cation and anion F = F − because it is Group 7 Cu = Cu 2+ to balance the two (−) charges from 2 F − 2.Name the cation Cu 2+ = copper(II) 3.Name the anion. F − = fluoride 4.Write the cation name first, then the anion name. copper(II) fluoride

Tro's "Introductory Chemistry", Chapter 5 32 Practice: Name the following compounds. 1.TiCl 4 2.Fe 2 S 3

Tro's "Introductory Chemistry", Chapter 5 33 Example: Writing Formula for Binary Ionic Compounds Containing Variable Charge Metal manganese(IV) sulfide 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Switch charge (without sign) each ion to become subscript for the other ion 4.Reduce subscripts to smallest whole number ratio 5.Check that the total charge of the cations cancels the total charge of the anions Mn 4+ S 2– Mn 4+ S 2− Mn 2 S 4 Mn = (1) × (4+) = +4 S = (2) × (2–) = −4 MnS 2

Tro's "Introductory Chemistry", Chapter 5 34 Practice: What are the formulas for compounds made from the following ions? 1) copper(II) nitride 2) iron(III) bromide

Tro's "Introductory Chemistry", Chapter 5 35 Compounds Containing Polyatomic Ions Polyatomic ions are single ions that contain more than one atom Name and charge of polyatomic ion do not change As usual, name any ionic compound by naming cation first and then anion

Some Common Polyatomic Ions NameFormula acetateC2H3O2–C2H3O2– carbonateCO 3 2– hydrogen carbonate HCO 3 – hydroxideOH – nitrateNO 3 – nitriteNO 2 – chromateCrO 4 2– dichromateCr 2 O 7 2– cyanideCN – permanganateMnO 4 – ammoniumNH 4 + NameFormula hypochloriteClO – chloriteClO 2 – chlorateClO 3 – perchlorateClO 4 – sulfateSO 4 2– sulfiteSO 3 2– hydrogen sulfateHSO 4 – hydrogen sulfiteHSO 3 – phosphatePO 4 3– phosphitePO 3 3–

Tro's "Introductory Chemistry", Chapter 5 37 Patterns for Polyatomic Ions 1.The ‘ate ’ and the ‘ite’ ions. Ions with same charge but one less oxygen atom. NO 3 – Nitrate NO 2 – Nitrite 2.hydrogen- prefix before name and add 1 to the charge CO 3 2– = carbonate  HCO 3 – = hydrogen carbonate

Tro's "Introductory Chemistry", Chapter 5 38 Periodic Pattern of Polyatomic Ions -ate groups 3A4A5A6A7A BO 3 3− borate CO 3 2− carbonate NO 3 − nitrate SiO 3 2− silicate PO 4 3− phosphate SO 4 2− sulfate ClO 3 − chlorate AsO 4 3− arsenate SeO 4 2− selenate BrO 3 − bromate TeO 4 2− tellurate IO 3 − iodate

Tro's "Introductory Chemistry", Chapter 5 39 Patterns for Polyatomic Ions -ate ion chlorate = ClO 3 – -ate ion + 1 O  same charge, per- prefix perchlorate = ClO 4 – -ate ion – 1 O  same charge, -ite suffix chlorite = ClO 2 – -ate ion – 2 O  same charge, hypo- prefix, -ite suffix hypochlorite = ClO –

Tro's "Introductory Chemistry", Chapter 5 40 Example: Writing Formula for Ionic Compounds Containing Polyatomic Ion Iron(III) phosphate 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Switch the charge (without sign) of each ion to become subscript for the other ion 4.Reduce subscripts to smallest whole number ratio. 5.Check that the total charge of the cations cancels the total charge of the anions Fe 3+ PO 4 3− Fe 3+ PO 4 3− Fe 3 (PO 4 ) 3 Fe = (1) × (3+) = +3 PO 4 = (1) × (3−) = −3 FePO 4

Tro's "Introductory Chemistry", Chapter 5 41 Practice: Write the chemical formula of the following compounds? aluminum sulfate chromium(II) hydrogencarbonate

Tro's "Introductory Chemistry", Chapter 5 42 Example—Naming Ionic with Polyatomic Ion, Na 2 SO 4 1.Identify cation Na is the cation because metals form positive charge. Is the metal Type I or Type II? Na is in Group 1A,  Type I. Hence, charge on Na is +1 Identify anion Anion is SO 4 Polyatomic, because it contains TWO OR MORE different types of elements

Tro's "Introductory Chemistry", Chapter Name the cation. Na + = sodium (Type I). 5.Name the anion. SO 4 2- = sulfate. 6.Write the name of the cation followed by the name of the anion. sodium sulfate. Example—Naming Ionic with Polyatomic Ion, Na 2 SO 4, Continued

Tro's "Introductory Chemistry", Chapter 5 44 Example—Naming Ionic with Polyatomic Ion, Fe(NO 3 ) 3 1.Identify cation Fe is the cation because metals form positive charge. Is the metal Type I or Type II? Fe is a transition metal,  Type II. Caution!!: Transition metals have variable charge, so we need to find out what the charge on the anion Identify anion Anion is NO 3 polyatomic because it contains TWO OR MORE different types of elements

Tro's "Introductory Chemistry", Chapter Name the anion. NO 3 - = nitrate 5.Name the cation. Fe 3+ = iron(III) (Type II). Based on the charge of the nitrate group 6.Write the name of the cation followed by the name of the anion. iron(III) nitrate. Example—Naming Ionic with Polyatomic Ion, Fe(NO 3 ) 3, Continued

Tro's "Introductory Chemistry", Chapter 5 46 Practice─Name the Following 1.NH 4 Cl 2.Ca(C 2 H 3 O 2 ) 2 3.Cu(NO 3 ) 2

Tro's "Introductory Chemistry", Chapter 5 47 Writing Names of Binary Molecular Compounds of Two Nonmetals 1.Write the name of the first element in the formula Use the full name of the element, 2.Write the name of the second element in the formula with an -ide suffix as if it were an anion—However, remember these compounds do not contain ions! 3.Use a prefix in front of each name to indicate the number of atoms a)Never use the prefix mono- on the first element.

Tro's "Introductory Chemistry", Chapter 5 48 Subscript—Prefixes 48 1 = mono- not used on first nonmetal 2 = di- 3 = tri- 4 = tetra- 5 = penta- 6 = hexa- 7 = hepta- 8 = octa- 9 = nona- 10 = deca- Drop last “a” or “o” if name begins with a vowel.

Tro's "Introductory Chemistry", Chapter 5 49 Example: Naming Binary Molecular. e.g., BF 3 1.Name the first element. boron 2.Name the second element with an -ide. fluorine  fluoride 3.Add a prefix to each name to indicate the subscript. monoboron trifluoride Drop the prefix mono from the first element. boron trifluoride

Tro's "Introductory Chemistry", Chapter 5 50 Practice: Name the following. N 2 O 4 PCl 5 I 2 F 7 CO

Tro's "Introductory Chemistry", Chapter 5 51 Example: Binary Molecular dinitrogen pentoxide Identify the symbols of the elements. nitrogen = N oxide = oxygen = O Write the formula using prefix number for subscript. di = 2, penta = 5 N2O5N2O5

Tro's "Introductory Chemistry", Chapter 5 52 Practice: Write formulas for the following. dinitrogen tetroxide sulfur hexafluoride diarsenic trisulfide

Tro's "Introductory Chemistry", Chapter 5 53 Acids Acids are molecular compounds that form H + when dissolved in water. To indicate the compound is dissolved in water, (aq) is written after the formula.  not named as acid if not dissolved in water sour taste (please never taste it!!) dissolve many metals like Zn, Fe, Mg; but not Au, Ag, Pt formula generally starts with H e.g., HCl, H 2 SO 4

Tro's "Introductory Chemistry", Chapter 5 54 Acids Dissolve in aqueous solution to form H + cation and anion Binary acids have H + cation and nonmetal anion Oxyacids have H + cation and polyatomic anion

Tro's "Introductory Chemistry", Chapter Identify the anion 2.Name the anion with an -ic suffix 3.Add a hydro- prefix to the anion name 4.Add the word acid to the end Naming Binary Acids

Tro's "Introductory Chemistry", Chapter 5 56 Example: Naming Binary Acids. e.g., HCl(aq) 1.Identify the anion Cl = Cl −, chloride because Group 7A 2.Name the anion with an -ic suffix Cl − = chloride  chloric 3.Add a hydro- prefix to the anion name hydrochloric 4.Add the word acid to the end hydrochloric acid

Tro's "Introductory Chemistry", Chapter 5 57 Naming Oxyacids 1)Identify the polyatomic ion (anion) The poly atomic ion in this case will always contain oxygen 2)If the polyatomic ion name ends in -ate, then change ending to -ic suffix 3)If the polyatomic ion name ends in -ite, then change ending to -ous suffix 4)Write word acid at the end of all names.

Tro's "Introductory Chemistry", Chapter 5 58 Example: Naming Oxyacids. HNO 3 (aq) 1.Identify the polyatomic ion NO 3 = NO 3 − = nitrate 2.If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous. NO 3 − = nitrate  nitric 3.Write the name of the anion followed by the word acid. nitric acid

Tro's "Introductory Chemistry", Chapter 5 59 Example: Naming Oxyacids. HNO 2 (aq) 1.Identify the polyatomic ion NO 2 = NO 2 − = nitrite 2.If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous. NO 2 − = nitrite  nitrous 3.Write the name of the anion followed by the word acid. nitrous acid

Tro's "Introductory Chemistry", Chapter 5 60 Example: Naming Oxyacids H 2 SO 4 (aq) 1.Identify the anion SO 4 = SO 4 2− = sulfate 2.If the anion has -ate suffix, change it to -ic. If the anion has -ite suffix, change it to -ous SO 4 2− = sulfate  3.Write the name of the anion followed by the word acid. sulfuric acid sulfuric

Tro's "Introductory Chemistry", Chapter 5 61 Practice: Name the following HBr (aq) HClO 3 (aq) H 3 PO 4 (aq)

Tro's "Introductory Chemistry", Chapter 5 62 Writing Formulas for Acids 1)when name ends in acid, formula starts with H 2)Hydro prefix means it is a binary acid, no prefix means it is an oxyacid 3)Locate the cation and the anion NB: In acids the cation is always H + 4)for oxyacid, if ending is -ic, polyatomic ion ends in -ate; if ending is -ous, polyatomic ion ends in –ite 5)write formulas as if ionic, even though it is molecular

Tro's "Introductory Chemistry", Chapter 5 63 Example: Binary Acids hydrobromic acid 1.Write the symbol for the cation and its charge. 2.Write the symbol for the anion and its charge. 3.Switch charges (without sign) for each ion to subscript for the other ion. 4.Add (aq) to indicate dissolved in water. H+H+ Br − H + Br − HBr HBr(aq) In all acids, the cation is H +. Hydro means binary.

Tro's "Introductory Chemistry", Chapter 5 64 Example: Oxyacids carbonic acid 1.Write the symbol for the cation and its charge 2.Write the symbol for the anion and its charge 3.Switch charge (without sign) for each ion to become subscript for the other ion 4.Add (aq) to indicate dissolved in water H+H+ CO 3 2− H + CO 3 2− H 2 CO 3 H 2 CO 3 (aq) In all acids, the cation is H +. No hydro means polyatomic ion. -ic means -ate ion.

Tro's "Introductory Chemistry", Chapter 5 65 Example: Oxyacids sulfurous acid 1.Write the symbol for the cation and its charge. 2.Write the symbol for the anion and its charge. 3.Switch charge (without sign) of each ion to become subscript for the other ion 4.Add (aq) to indicate dissolved in water. H+H+ SO 3 2− H + SO 3 2− H 2 SO 3 H 2 SO 3 (aq) In all acids, the cation is H +. No hydro means polyatomic ion. -ous means -ite ion.

Tro's "Introductory Chemistry", Chapter 5 66 Practice: What are the formulas for the following acids? chlorous acid phosphoric acid hydrobromic acid

Compounds With Trivial Names NameFormula WaterH2OH2O MethaneCH 4 AmmoniaNH 3 Tro's "Introductory Chemistry", Chapter 5 67

Tro's "Introductory Chemistry", Chapter 5 68 Formula-to-Name Flowchart

Tro's "Introductory Chemistry", Chapter 5 69 Formula Mass The mass of an individual molecule or formula unit. Also known as molecular mass or molecular weight. Sum of the masses of the atoms in a single molecule or formula unit. Whole = Sum of the parts. Mass of 1 molecule of H 2 O = 2(1.01 amu H) amu O = amu.

Tro's "Introductory Chemistry", Chapter 5 70 Example—Calculate the Formula Mass of Al 2 (SO 4 ) 3

Tro's "Introductory Chemistry", Chapter 5 71 Practice—Calculate the Formula Mass of Fe 2 (CO 3 ) 3 Answer = amu

Tro's "Introductory Chemistry", Chapter 5 72 Recommended Study Problems Chapter 5 NB: Study problems are used to check the student’s understanding of the lecture material. Students are EXPECTED TO BE ABLE TO SOLVE ALL THE SUGGESTED STUDY PROBLEMS. If you encounter any problems, please talk to your professor or seek help at the HACC-Gettysburg learning center. Questions from text book Chapter 5, p , 25, 29, 31, 33, 35, 39, 41, 49, 51, 55, 57, 61, 63, 67, 69, ANSWERS -The answers to the odd-numbered study problems are found at the back of your textbook