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.

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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

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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

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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

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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

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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

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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

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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!

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Writing Formulas

Writing Chemical Formulas: Ionic Compounds

I.  IonicCompounds§ Balancecharges,sincecompoundsmustbeneutral!Posi;veCharge+Nega;veCharge=0

Examples•  magnesiumbromideMgBr2•  iron(II)sulfide FeS

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Writing Chemical Formulas: Molecular Compounds

II.  BinaryMolecularCompounds§  Greekprefixesindicatenumberof atoms.

Examples•  dinitrogenpentoxideN2O5 •  borontrifluorideBF3

GreekPrefixesmono onedi twotri threetetra fourpenta fivehexa six

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Strategy for Writing Formulas of Compounds

Metal+Nonmetalor

PolyatomicIons

IONICcompound

Nonmetal+NonmetalSeeGreekprefixes

COVALENTcompound

Balancecharges!FollowGreekprefixes!

Lookatthename.

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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

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