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1、Roy KennedyMassachusetts Bay Community CollegeWellesley Hills,MA,Introductory Chemistry,3rd EditionNivaldo Tro,Chapter 5Molecules andCompounds,2009,Prentice Hall,Tros Introductory Chemistry,Chapter 5,2,Molecules and Compounds,SaltSodiumshiny,reactive,poisonous.Chlorinepale yellow gas,reactive,poison
2、ous.Sodium chloridetable salt.SugarCarbonpencil or diamonds.Hydrogenflammable gas.Oxygena gas in air.Combine to form white crystalline sugar.,Tros Introductory Chemistry,Chapter 5,3,Law of Constant Composition,All pure substances have constant composition.All samples of a pure substance contain the
3、same elements in the same percentages(ratios).Mixtures have variable composition.,Tros Introductory Chemistry,Chapter 5,4,Compounds Display Constant Composition,If we decompose water by electrolysis,we find 16.0 grams of oxygen to every 2.00 grams of hydrogen.Water has a constant mass ratio of oxyge
4、n to hydrogen of 8.0.,Example 5.1Show that Two Samples of Carbon Dioxide Are Consistent with the Law of Constant Composition.,Since both samples have the same proportion of elements,carbon dioxide shows constant composition.,Compare:,Solution:,composition=mass O:mass C,Solution Map:Relationships:,Sa
5、mple 1:4.8 g O,1.8 g C;Sample 2:17.1 g O,6.4 g Cproportion O:C,Given:Find:,Tros Introductory Chemistry,Chapter 5,6,PracticeShow that Hematite Has Constant Composition if a 10.0 g Sample Has 7.2 g Fe and the Rest Is Oxygen;and a Second Sample Has 18.1 g Fe and 6.91 g O.,Example 5.1Show that Two Sampl
6、es of Hematite Are Consistent with the Law of Constant Composition.,Since both samples have the same proportion of elements,hematite shows constant composition.,Compare:,Solution:,composition=mass Fe:mass O,Solution Map:Relationships:,Sample 1:7.2 g Fe,(10.0-7.2)=2.8 g O;Sample 2:18.1 g Fe,6.91 g Op
7、roportion Fe:O,Given:Find:,Tros Introductory Chemistry,Chapter 5,8,Why Do Compounds ShowConstant Composition?,The smallest piece of a compound is called a molecule.If you have a pure substance,then every molecule will have the same number and type of atoms.Therefore,your compound have the same predi
8、ctable properties(physical&chemical).,Tros Introductory Chemistry,Chapter 5,9,Formulas Describe Compounds,Elements are represented by a letter symbol.A pure compound is composed of atoms of two or more elements.The number of each element is written to the right of the element as a subscript.If there
9、 is only one atom,the 1 subscript is not written.Polyatomic groups are placed in parentheses.If more than one.,10,Formulas Describe Compounds,Continued,Water=H2O two atoms of hydrogen and 1 atom of oxygen,Table salt=NaCl,one sodium and one chlorine atom:notice that pure substances have consistent st
10、ructures,these pure substance will also have consistent physical and chemical properties.,Tros Introductory Chemistry,Chapter 5,11,Order of Elements in a Formula,Metals are written first.NaClNonmetals are written in order from Table 5.1.CO2There are occasional exceptions for historical or informatio
11、nal reasons.H2O,but NaOH.,Tros Introductory Chemistry,Chapter 5,12,PracticeWrite Formulas for Each of the Following Compounds.,HematiteComposed of four oxide ions for every three iron ions.AcetoneEach molecule contains six hydrogen atoms,three carbon atoms,and one oxygen atom.,Fe3O4,C3H6O,Tros Intro
12、ductory Chemistry,Chapter 5,13,Molecules with Polyatomic Ions,Mg(NO3)2Compound calledmagnesium nitrate.,CaSO4Compound calledcalcium sulfate.,14,Molecules with Polyatomic Ions,Continued,Mg(NO3)2Compound calledmagnesium nitrate.,CaSO4Compound calledcalcium sulfate.,Tros Introductory Chemistry,Chapter
13、5,15,PracticeDetermine the Total Number of Atoms or Ions in One Formula Unit of Each of the Following.,Mg(C2H3O2)2(Hg2)3(PO4)2,1 Mg+4 C+6 H+4 O=15,6 Hg+2 P+8 O=16,16,Classifying Materials,Atomic elements=are single atoms.Molecular elements=multi-atom molecules.Molecular compounds=molecules made of o
14、nly nonmetals.Ionic compounds=Compounds made of cations and anions.,17,More about Molecular Elements,Certain elements occur as diatomic molecules.7 diatomic elementsThe Rule of 7s Find the element with atomic number 7,N.Make a figure 7 by going over to Group 7A,then down.The seventh element is H2.,H
15、2,Cl2,Br2,I2,7,7A,N2 O2 F2,Molecular Compounds,Two or more nonmetals.Smallest unit is a molecule.,Tros Introductory Chemistry,Chapter 5,19,Ionic Compounds,Metals+nonmetals.No individual molecule units,instead have a 3-dimensional array of cations and anions made of formula units.,20,Molecular View o
16、f Elements and Compounds,Tros Introductory Chemistry,Chapter 5,21,Classify Each of the Following as Either an Atomic Element,Molecular Element,Molecular Compound,or Ionic Compound,Continued.,Aluminum,Al=Atomic element.Aluminum chloride,AlCl3=Ionic compound.Chlorine,Cl2=Molecular element.Acetone,C3H6
17、O=Molecular compound.Carbon monoxide,CO=Molecular compound.Cobalt,Co=Atomic element.,Tros Introductory Chemistry,Chapter 5,22,Ionic Compounds,Ionic compounds are made of ions called cations and anions.Cations=+charged ions;anions=charged ions.The sum of the+charges of the cations must equal the sum
18、of the charges of the anions.If Na+is combined with S2-,you will need 2 Na+ions for every S2-ion to balance the charges,therefore the formula must be Na2S.,Tros Introductory Chemistry,Chapter 5,23,Writing Formulas for Ionic Compounds,Write the symbol for the metal cation and its charge.Write the sym
19、bol for the nonmetal anion and its charge.Charge(without sign)becomes subscript for the other ion.Reduce subscripts to smallest whole-number ratio.Check that the sum of the charges of the cation cancels the sum of the anions.,Tros Introductory Chemistry,Chapter 5,24,Write the Formula of a Compound M
20、ade from Aluminum Ions and Oxide Ions.,Write the symbol for the metal cation and its charge.Write the symbol for the nonmetal anion and its charge.Charge(without sign)becomes subscript for the other ion.Reduce subscripts to smallest whole-number ratio.Check that the total charge of the cations cance
21、ls the total charge of the anions.,Al+3 column 3A,O2-column 6A,Al+3 O2-,Al2O3,Al=(2)(+3)=+6O=(3)(-2)=-6,Tros Introductory Chemistry,Chapter 5,25,PracticeWhat Are the Formulas for Compounds Made from the Following Ions?,Potassium ion with a nitride ion.K+with N3-K3NCalcium ion with a bromide ion.Ca+2
22、 with Br-CaBr2Aluminum ion with a sulfide ion.Al+3 with S2-Al2S3,Tros Introductory Chemistry,Chapter 5,26,PracticeWhat Are the Formulas for Compounds Made from the Following Ions?,Copper(II)ion with a nitride ion.Iron(III)ion with a bromide ion.,Tros Introductory Chemistry,Chapter 5,27,PracticeName
23、the Following Compounds.,Ti4+Cl-Pb2+Br-Fe3+S2-,Tros Introductory Chemistry,Chapter 5,28,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
24、1 molecule of H2O=2(1.01 amu H)+16.00 amu O=18.02 amu.,Tros Introductory Chemistry,Chapter 5,29,PracticeCalculate the Formula Mass of,Al2(SO4)3Cr(HCO3)2,End:if Lab is on nomenclature,Tros Introductory Chemistry,Chapter 5,30,Tros Introductory Chemistry,Chapter 5,31,Formula-to-NameStep 1,Is the compou
25、nd one of the exceptions to the rules?,Tros Introductory Chemistry,Chapter 5,32,Common NamesExceptions,H2O=Water,steam,ice.NH3=Ammonia.CH4=Methane.NaCl=Table salt.C12H22O11=Table sugar.,Tros Introductory Chemistry,Chapter 5,33,Formula-to-NameStep 2,What major class of compound is it?Ionic or Molecul
26、ar?,Tros Introductory Chemistry,Chapter 5,34,Major Classes,Ionic compounds.Metal+nonmetal(s).Metal first in formula.Binary ionic or compounds with polyatomic ions.Molecular compounds.2 or more nonmetals.Binary molecular(or binary covalent).2 nonmetals.AcidsFormula starts with H.Though acids are mole
27、cular,they behave as ionic when dissolved in water.May be binary or oxyacid.,Tros Introductory Chemistry,Chapter 5,35,Formula-to-NameStep 3,What major subclass of compound is it?Binary Ionic,Ionic with Polyatomic Ions,Binary Molecular,Binary Acid,or Oxyacid?,Tros Introductory Chemistry,Chapter 5,36,
28、Classifying Compounds,Compounds containing a metal and a nonmetal=Binary ionic.Type I and II.Compounds containing a polyatomic ion=Ionic with polyatomic ion.Compounds containing two nonmetals=Binary molecular compounds.Compounds containing H and a nonmetal=Binary acids.Compounds containing H and a p
29、olyatomic ion=Oxyacids.,Tros Introductory Chemistry,Chapter 5,37,Formula-to-NameStep 4,Apply rules for the class and subclass.,Tros Introductory Chemistry,Chapter 5,38,Formula-to-NameRules for Ionic,Made of cation and anion.Name by simply naming the ions.If cation is:Type I metal=Metal name.Type II
30、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.,Tros Introductory Chemistry,Chapter 5,39,Monatomic Nonmetal Anion,Determine the charge from position on the periodic table.To name anion,change ending
31、 on the element name to ide.,Tros Introductory Chemistry,Chapter 5,40,Metal Cations,Type I Metals whose ions can only have one possible charge.1A,2A,(Al,Zn,Ag).Determine charge by position on the periodic table.1A=+,2A=2+,Al=3+.Some need to be memorized.Zn=2+,Ag=+.Type IIMetals whose ions can have m
32、ore than one possible charge.Determine charge by charge on anion.,How do you know a metal cation is Type II?,Tros Introductory Chemistry,Chapter 5,41,Determine if the Following Metals are Type I or Type II.If Type I,Determine the Charge on the Cation it Forms.,Lithium,Li.Copper,Cu.Gallium,Ga.Tin,Sn.
33、Strontium,Sr.,Tros Introductory Chemistry,Chapter 5,42,Determine if the Following Metals are Type I or Type II.If Type I,Determine the Charge on the Cation it Forms,Continued.,Lithium,LiType I1+Copper,CuType IIGallium,GaType I3+Tin,SnType IIStrontium,SrType I2+,Tros Introductory Chemistry,Chapter 5,
34、43,Type I Binary Ionic Compounds,Contain metal cation+nonmetal anion.Metal listed first in formula and name.Name metal cation first,name nonmetal anion second.Cation name is the metal name.Nonmetal anion named by changing the ending on the nonmetal name to ide.,Tros Introductory Chemistry,Chapter 5,
35、44,ExampleNaming Binary Ionic,Type I Metal,CsF,Is it one of the common exceptions?H2O,NH3,CH4,NaCl,C12H22O11=No!Identify major class.Cs is a metal because it is on the left side of the periodic table.F is a nonmetal because it is on the right side of the periodic table.Ionic.Identify the subclass.2
36、elements,Binary ionic.Is the metal Type I or Type II?Cs is in Group 1A,Type I.,Tros Introductory Chemistry,Chapter 5,45,ExampleNaming Binary Ionic,Type I Metal,CsF,Continued,Identify cation and anion.Cs=Cs+because it is Group 1A.F=F-because it is Group 7A.Name the cation.Cs+=cesium.Name the anion.F-
37、=fluoride.Write the cation name first,then the anion name.cesium fluoride.,Tros Introductory Chemistry,Chapter 5,46,PracticeName the Following Compounds.,KClMgBr2Al2S3,Tros Introductory Chemistry,Chapter 5,47,PracticeName the Following Compounds,Continued.,KClpotassium chloride.MgBr2magnesium bromid
38、e.Al2S3aluminum sulfide.,Tros Introductory Chemistry,Chapter 5,48,Type II Binary Ionic Compounds,Contain metal cation+nonmetal anion.Metal listed first in formula and name.Name metal cation first,name nonmetal anion second.Metal cation name is the metal name followed by a roman numeral in parenthese
39、s to indicate its charge.Determine charge from anion charge.Common Type II cations in Table 5.5.Nonmetal anion named by changing the ending on the nonmetal name to ide.,Tros Introductory Chemistry,Chapter 5,49,Determining the Charge on a Variable Charge CationAu2S3,Determine the charge on the anion.
40、Au2S3-the anion is S,since it is in Group 6A,its charge is 2.Determine the total negative charge.Since there are 3 S in the formula,the total negative charge is 6.Determine the total positive charge.Since the total negative charge is 6,the total positive charge is+6.Divide by the number of cations.S
41、ince there are 2 Au in the formula and the total positive charge is+6,each Au has a 3+charge.,Tros Introductory Chemistry,Chapter 5,50,ExampleWriting Formula for a Binary Ionic Compound Containing Variable Charge Metal,Manganese(IV)Sulfide,Write the symbol for the cation and its charge.Write the sym
42、bol for the anion and its charge.Charge(without sign)becomes subscript for the other ion.Reduce subscripts to smallest whole-number ratio.Check that the total charge of the cations cancels the total charge of the anions.,Mn+4,S2-,Mn+4 S2-,Mn2S4,Mn=(1)(+4)=+4S=(2)(-2)=-4,MnS2,Tros Introductory Chemis
43、try,Chapter 5,51,PracticeWhat Are the Formulas for Compounds Made from the Following Ions?,Copper(II)ion with a nitride ion.Iron(III)ion with a bromide ion.,Tros Introductory Chemistry,Chapter 5,52,PracticeWhat Are the Formulas for Compounds Made from the Following Ions?,Continued,Cu2+with N3-Cu3N2F
44、e+3 with Br-FeBr3,Tros Introductory Chemistry,Chapter 5,53,ExampleNaming Binary Ionic,Type II Metal,CuCl,Is it one of the common exceptions?H2O,NH3,CH4,NaCl,C12H22O11=No!Identify major class.Cu is a metal because it is on the left side of the periodic table.Cl is a nonmetal because it is on the righ
45、t side of the periodic table.Ionic.Identify the subclass.2 elements,Binary ionic.Is the metal Type I or Type II?Cu is not in Group 1A,2A,or(Al,Zn,Ag)Type II.,Tros Introductory Chemistry,Chapter 5,54,ExampleNaming Binary Ionic,Type II Metal,CuCl,Continued,Identify cation and anion.Cl=Cl because it is
46、 Group 7A.Cu=Cu+to balance the charge.Name the cation.Cu+=Copper(I).Name the anion.Cl=Chloride.Write the cation name first,then the anion name.Copper(I)chloride.,Tros Introductory Chemistry,Chapter 5,55,PracticeName the Following Compounds.,TiCl4PbBr2Fe2S3,Tros Introductory Chemistry,Chapter 5,56,Pr
47、acticeName the Following Compounds,Continued.,TiCl4Titanium(IV)chloride.PbBr2Lead(II)bromide.Fe2S3Iron(III)sulfide.,Cl=4(1)=4Ti=+4=1(4+),Br=2(1)=2Pb=+2=1(2+),S=3(2)=6Pb=+6=2(3+),Tros Introductory Chemistry,Chapter 5,57,Compounds Containing Polyatomic Ions,Polyatomic ions are single ions that contain
48、 more than one atom.Name any ionic compound by naming cation first and then anion.Non-polyatomic cations named like Type I and II.Non-polyatomic anions named with ide.,Some Common Polyatomic Ions,Tros Introductory Chemistry,Chapter 5,59,ExampleWriting Formula for an Ionic Compound Containing Polyato
49、mic Ion,Iron(III)phosphate,Write the symbol for the cation and its charge.Write the symbol for the anion and its charge.Charge(without sign)becomes subscript for the other ion.Reduce subscripts to smallest whole-number ratio.Check that the total charge of the cations cancels the total charge of the
50、anions.,Fe+3,PO43-,Fe+3 PO43-,Fe3(PO4)3,Fe=(1)(+3)=+3PO4=(1)(-3)=-3,FePO4,Tros Introductory Chemistry,Chapter 5,60,PracticeWhat Are the Formulas for Compounds Made from the Following Ions?,Aluminum ion with a sulfate ion.Chromium(II)with hydrogencarbonate.,Tros Introductory Chemistry,Chapter 5,61,Pr
