Post on 24-Sep-2020
Ch 5. Molecules and Compounds
Chem 30A
Chemical Formulas of Compounds
1. Agivencompoundalwayshasthesamenumbersandtypesofatoms(constantcomposi;on).
2. Eachatomisrepresentedbyitselementsymbol.3. Thenumberofeachtypeofatomisindicatedbya
subscripttotherightoftheelementsymbol(Excep;on:Ifjustoneatom,nosubscript).
4. Typically,themoremetallicelementislistedfirst.
ExProbs
Molecular Compounds and Ionic Compounds
Types of Compounds
MolecularCompounds• Covalentbond• Oneunit:Molecule
O HH
IonicCompounds• Ionicbond• Oneunit:Formulaunit
+ –
Chemical Bond
Chemicalbond:Aforcethatholdsgroupsofatomstogetherandmakesthemfunc;onasaunit.• Bondinginvolvesjusttheelectronsofatoms!
Molecular (Covalent) Compounds
• HeldtogetherthroughCovalentBonds:Bondsinwhichelectronsaresharedbetweenthebondedatoms.
• Molecule:agroupoftwoormoreatomswhicharecovalentlybonded(aunitofmolecularcompound)
• Nonmetal+NonmetalàMolecularCompound
H H H2
Molecules
• Note:Bothcompounds(eg,H2O)andelements(eg.O2,H2)mayexistasmolecules.
OH H
H
H
H
HC C O O
Cl Cl
Compounds Elements
Representing Molecules
CH4
Chemicalformula
Ball-and-s;ckmodel
Structuralformula Space-fillingmodel
C
H
H
H
H
Ionic Compounds
• HeldtogetherthroughIonicBonds:Bondsinwhichoppositely-chargedionsareheldtogetherbyelectrosta;caUrac;onbetweenthem.
• Formulaunit:Agroupoftwoormoreionswhichareboundthroughionicbonds(aunitofioniccompound)
• Metal+NonmetalàIonicCompound
+ –
Formula Units
• Formulaunitsexistasapartofalarger3Darray(asolid).
Ionic Compounds
• Mostcommonly,ioniccompoundsformwhenmetalscombinewithnonmetalsàMetalelementtransferselectronstothenonmetalelement.
Metalca;on+NonmetalanionàioniccompoundIsolatedionsdon’texist!
Formation of an Ionic Compound
Overview: Fundamental Components of Matter
Matter
PureSubstances• Elements• Compounds
“Par;cles”ofMaUer• Atoms• Ions• Molecules
Elements, Compounds, Atoms, Molecules, Ions
Elements(1typeofatom)
• Atomic
• Molecular
Compounds(morethan1typeofatom)
• Ionic• Molecular
+ –
Elements, Compounds, Atoms, Molecules, Ions
ExProbs
Formula (Molecular) Mass
Formula (Molecular) Masses of Compounds
Formulamassofacompound=sumofatomic masses
eg.MolecularmassofH2O =2(atomicmassofH)+1(atomicmassofO) =2(1.008amu)+1(16.00amu) =18.02amu
ExProbs
Chemical Nomenclature
Chemical Nomenclature
• ChemicalNomenclature:asystemofnamingchemicalsubstances
CommonName Systema-cName Formula
Grainalcohol Ethylalcohol CH3OHRubbingalcohol Isopropylalcohol C2H5OHLaughinggas Dinitrogenoxide N2OMilkofmagnesia
Magnesiumhydroxide
Mg(OH)2
Epsomsalt Magnesiumsulfateheptahydrate
MgSO4�7H2O
Chemical Nomenclature
A. IonicCompounds(BinaryandPolyatomic)B. CovalentCompounds(Binary)C. Acids
Formulas(NaCl)Names(sodiumchloride)RefertoChemicalNomenclatureHandoutforrulesfornamingandwri;ngformulas.
Naming Compounds
NamingBinaryIonicCompounds
• Theca;onisalwaysnamedfirstandtheanionsecond.
• Remember:Ioniccompoundhasanetchargeof0.
• METAL+NONMETAL=ioniccompound
NamingBinaryIonicCompounds:FixedChargeCa;on
Ioniccompoundscontainingfixed-chargemetals(mostlymaingroupmetals):1. Amonatomicca;onhasthesamenameasthat
oftheparentelement.2. Amonatomicanionisnamedbytakingtheroot
oftheelementnameandadding–ide.• Examples
KCl potassiumchlorideMgBr2 magnesiumbromideCaO calciumoxide
ExProbs
Naming Binary Ionic Compounds: Variable Charge Cations
Ioniccompoundscontainingvariable-chargeca;ons(mostlytransi;onmetals):Formetalsthatcanformca;onsofmorethanonecharge,thechargeonthemetalionmustbespecifiedwithRomannumeralinparentheses!• Examples
CuBr Copper(I)bromideFeS Iron(II)sulfidePbO2 Lead(IV)oxide
Common Ion Charges (Memorize!)
Metalsformca;ons.• Groups1A,2A,3A:
charge=group#• Transi;onsmetals:
Manyhavevariablecharges.
Nonmetalsformanions.• Group5A:charge=-3• Group6A:charge=-2• Group7A(halogens):
charge=-1• Group8A(noblegases):
charge=0
ExProbs
Naming Ionic Compounds with Polyatomic Ions
Ionscanbesimple(monatomic)orpolyatomic.• SimpleIons:Mg2+,Li+,Cl-,O2-
• PolyatomicIons: NH4
+ NO3-
N N
NH4+ NO3
-
Naming Ionic Compounds with Polyatomic Ions
Namesandchargesofpolyatomicionsmustbememorized.(Memorizethefollowing!)• Polyatomicca;ons:Namesendin-ium. NH4
+=ammonium H3O+=hydronium• Polyatomicanions:Manycontainoxygen. OH–=hydroxide CO3
2–=carbonate NO3
–=nitrate PO43–=phosphate
SO42–=sulfate CN–=cyanide
Common Polyatomic Ions
Naming Ionic Compounds with Polyatomic Ions
Examplesofioniccompoundswithpolyatomicions• NH4Clammoniumchloride• Na2CO3sodiumcarbonate• Mn(OH)2manganese(II)hydroxide• (NH4)2SO4ammoniumsulfate
ExProbs
Naming Binary Molecular (Covalent) Compounds
NONMETAL+NONMETALNamefirstelementfirst,secondelementsecond.1. Firstelement:Greekprefix+
parentelement(Excep;on:Don’tuse“mono-”).
2. Secondelement:Greekprefix+parentelement+“-ide”(asifitwereananion).
Naming Binary Covalent Compounds
ExamplesofBinaryMolecularCompoundsN2O5 dinitrogenpentoxideP4O6 tetraphosphorushexoxideBF3 borontrifluorideNO nitrogenmonoxideCO carbonmonoxide
Exprobs
Naming Problem
Whichofthefollowingcompoundsis/arenamedincorrectly?a) KNO3 potassiumnitrateb) TiO2 ;tanium(II)oxidec) Sn(OH)4 ;n(IV)hydroxided) PBr5 phosphoruspentabromidee) CaCrO4 calciumchromate
Strategy for Naming Compounds
Metal+Nonmetalor
PolyatomicIons
Nonmetal+NonmetalLookattheformula.
IONICCompoundNameasCa*on+Anion!
(Ifseevariable-chargeca*on,includechargeinRoman
numerals!)
MOLECULARCompound
UseGreekprefixes!
Exprobs
Writing Formulas
Writing Chemical Formulas: Ionic Compounds
I. IonicCompounds§ Balancecharges,sincecompoundsmustbeneutral!Posi;veCharge+Nega;veCharge=0
Examples• magnesiumbromideMgBr2• iron(II)sulfide FeS
Exprobs
Writing Chemical Formulas: Molecular Compounds
II. BinaryMolecularCompounds§ Greekprefixesindicatenumberof atoms.
Examples• dinitrogenpentoxideN2O5 • borontrifluorideBF3
GreekPrefixesmono onedi twotri threetetra fourpenta fivehexa six
Exprobs
Strategy for Writing Formulas of Compounds
Metal+Nonmetalor
PolyatomicIons
IONICcompound
Nonmetal+NonmetalSeeGreekprefixes
COVALENTcompound
Balancecharges!FollowGreekprefixes!
Lookatthename.
Exprobs
Nomenclature for Acids
Brief Intro to Acids and Bases
ArrheniusDefini;onofAcidsandBases• Acid:asubstancethatmakesproton(H+)inwater.HCl àH+ +Cl-
acidprotonanion
• Base:asubstancethatmakeshydroxides(OH–)inwater.NaOHàNa++OH–
Brief Intro to Acids and Bases
Bronsted-LowryDefini;onofAcidsandBases• Acidsareproton(H+)donors.HCl àH+ +Cl-
acidprotonanion
• Basesareproton(H+)acceptors. NH3+H+àNH4
+
baseprotonca;on
Strong and Weak Acids
• Strongacid:Completelyionized(dissociated).HCl(aq) H+(aq)+Cl-(aq)
• Weakacid:Mostoftheacidmoleculesremainintact.
CH3COOH(aq) H+(aq)+CH3COO-(aq) equilibriumarrow
Naming Acids
*Acidsalwayshave“H”firstintheirformulas!Endallacidnameswith“acid.”1. BinaryAcids:
Nameformat:“hydro-”+parentelement +“-icacid”
Naming Acids
2. Acidwithoxygen(Oxyacids):Acidnameisderivedfromoxoanionofthatacid.• Ifanionendsin“ate”àacidnameendswith“ic”
acid.§ NO3
–isnitrateà HNO3isnitricacid
• Ifanionofendsin“ite”àacidnameendswith“ous”acid.§ NO2
–isnitriteàHNO2isnitrousacid
Some Oxyacids
Common Acids (Memorize!)
StrongAcids• HCl hydrochloricacid• HBr hydrobromicacid• HI hydroiodicacid• HNO3 nitricacid• H2SO4 sulfuricacid• HClO4 perchloricacid
WeakAcid• HC2H3O2 orCH3COOHace;cacid• H2CO3 carbonicacid
Exprobs