1

Name:__________________________________________[ ] Date:____________Class:3____LearningObjectivesforIonicBondinga) describetheformationofionsbyelectronloss/gaininordertoobtaintheelectronicstructureof

aninertgasb) describe the formation of ionic (electrovalent) bonds betweenmetals and nonmetals as the

electrostaticforcewhichholdstwooppositelychargedionstogether.,e.g.NaCl,MgCl2andMgO,includingtheuseofdotandcrossdiagrams

c) state that ionicmaterials contain a giant lattice in which the ions are held by electrostaticattraction,e.g.NaCl(candidateswillnotberequiredtodrawdiagramsofioniclattices)

d) deducetheformulaeofotherioniccompoundsfromdiagramsoftheirlatticestructures,limitedtobinarycompounds

e) relate thephysicalproperties (includingelectricalproperty)of ioniccompounds to their latticestructure

LearningObjectivesforMetallicBondinga) describemetallicbonding in termsofa latticeofpositive ionssurroundedbyamobile

electrons('seaofelectrons')b) relate the electrical conductivity of metals to the mobility to the electrons in the

structure

ChemistryChemicalBondingIonic&MetallicNotes1

2

1. WHYARECHEMICALBONDFORMED?

a. Thechemicalbondingeneralisanelectrostaticattractionbetweentwoatoms.Itinvolvestheattractionsbetweenelectronsofoneatomforthepositivenucleusoftheotheratom.

b. Bondingoccurswhentheattractionbetweenatomsovercomesthethermalenergywhich

tendstokeeptheatomsapart.

e- e-

e-e-repulsion

attraction

1.1 OctetRule

a. All noble gases (except helium) have 8 valence electrons very stable electronic

arrangementsb. Atomsoftenlose,gainorshareelectronstoachievethesamedupletoroctetstructureof

anoblegas.c. Electrondotsymbol

valenceelectronsareinvolvedinbondingbetweenatoms soitisimportanttorepresenttheminausefulwayusingtheelectrondotsymbol

thesymboloftheelementisinthemiddleandstandsforALLthecoreelement dotsrepresentsthevalenceelectronsandareplacedaroundtheelement amaximumof2electronsisallowedonanyoneside unpaired electrons are represented by a single dot, while paired electrons are

representedbytwodots

3

1.2 PatternsinthePeriodicTable a. Atomsarearrangedaccordingtoincreasingproton(atomic)numbers! b. Theperiodic tablecanbedivided into fourblocksofelements elementswithhighest

energyelectronsins,p,dandfsubshells c. The arrangement of the elements in the periodic table correlates with the

subshellthatholdsthehighestenergyelectrons. d. PatternsinthePeriodicTable i. Numberofelectronsintheoutershellrepeatsitselfinaregularpattern! (1) Elementswiththesamenumberofouterelectronsareputtogether. Elements are divided into a number of horizontal rows called Periods

numbered1,2,. Elements with the same number of outer electrons are arranged in a

verticalcolumncalledaGroupnumberedI,IIIII,. (2) Acrossaperiod, thenumberofelectrons in theouter shell increasesbyone

duetoincreaseinprotonnumber PeriodNo=Noofelectronshellsoccupiedbyelectrons(orhighestprincipal

quantumnumbern) e.g.helium1s2inperiod1 lithium1s22s1inperiod2 sodium1s22s22p63s1inperiod3 (3) Down a Group, there is an additional inner shell of core electrons, but the

numberofelectronsintheoutershellisthesame. GroupNo=Numberofelectronsintheoutershell e.g.lithium1s22s1inGroupI sodium1s22s22p63s1inGroupI potassium1s22s22p63s23p64s1inGroupI ii. SizeofAtoms (1) AcrossaPeriod,sizeofatomdecreases! Increasingnuclearcharge(butelectronaddedtothesameoutermostshell) (2) DownaGroup,sizeofatomincreases! Electronsaddedtotheoutershellareshieldedeffectivelyfromtheincreasein

nuclearcharge(bytheinnershells) Largeincreaseinthesizeofthelastatom(Group0elements) size of nuclear charge no longer as effective in attracting the outermost

shellelectrons.

4

iii. TypesofElements

(1) Elementswithfewnumbersofelectrons(1,2or3)intheoutershellaremetals. GroupI,IIandIII:Metals Atomsarerelativelybigger (2) Elementswithlargernumbersofelectrons(6or7) intheoutershellarenon

metals. GroupVIandVII:Nonmetals Atomsarerelativelysmaller (3) MixtureofmetalsandnonmetalsfoundinGroupIVandV. NonmetalsMetals Metalsarefoundatthetopleftsideandbottomoftheperiodictable. Nonmetalsareformedontherightsideandtopoftheperiodictable. Acrossaperiod,theelementschangesfrommetaltononmetal.

iv. Group0Elements

(1) Havecompletelyfilledoutershellsofelectrons

Atom ElectronicConfiguration StructureHe 1s2 dupletNe 1s22s22p6 octetAr 1s22s22p63s23p6 octet

(2) Arestableatomsi.e.unreactiveorhardlyformbondswithotheratoms,called

theinertgases!

5

1.3 FormationofIons

a. Atomsoftheotherelementstrytobecomeliketheinertgases bylosingorgainingelectronstoformandupletoroctetelectronicconfiguration toachieveacompletelyfilledoutershellofelectrons formationofchargedparticlescalledions(eitherpositiveandnegative)

b. Positiveionscalledcationsareformedwhenatomslosetheirvalenceelectrons Negativeionscalledanionsareformedwhenatomsgainelectrons c. FormationofPositiveIons i. Lossofelectronstendstooccur inatomswithfewvalenceelectrons(1,2or3) i.e.

metalatoms ii. Formspositivelychargedparticlescalledcations e.g.11Na:1s22s22p63s1tendstoloseitsvalenceelectrontoformsodiumion 1s22s22p63s11s22s22p6(octetstructure) iii. Representation:NaNa++e

iv. UsingelectrondotdiagramNa Na e-

Cations of most representative elements have no valence shell electronsshown.

d. FormationofNegativeIons i. Gainofelectronstendstooccurinatomswithlargernumberofvalenceelectrons(5,

6or7)i.e.nonmetalatoms ii. Formsanegativelychargedparticlecalledanion e.g.9F:1s22s22p5tendstogainanelectrontoformafluorideion 1s22s22p51s22s22p6(octetstructure) iii. Representation:F+eF iv. Usingelectrondotdiagram

F e- F

Mostmonatomicanionshaveeightvalenceelectronsshown. e. TrendsinIonicRadii i. Atomsarealwayslargerthananyoftheircations.

ii. Anionsarelargerthantheatomsfromwhichtheyarederived.

6

1.4 IonicBonding

a. An ionic bond is a chemical bond formed by the electrostatic attraction between thepositiveandnegativeions.

b. Formationofanionicbondcanbeviewedasatransferofelectronsfromametallicatomtoanonmetallicatom(bothtogainstabledupletoroctetstructure

1.5 FormingIonicNaCl

a. Electrontransferfromsodiumtochlorineinsodiumchloride.

Na[Ne]3s1 + Cl[Ne]3s23p5 Na+[Ne] + Cl[Ar]b. Bothattaintheelectronicconfigurationofthenearestnoblegas(octet).c. Positive sodium ions and thenegative chloride ions are attracted to each otherby an

electrostaticforce,alsoknownastheionic(orelectrovalent)bond.d. Anioniccompoundisformed.e. Formula:NaCl

1.6 DotandCrossDiagrams

Exercise:Drawionicdotandcrossstructuresforthefollowing(Indicateonlyvalenceelectrons

indotcrossdiagrams)

a. CaF2

c. Na2O

b. Mg3N2

d. MgCl2

7

1.7 IonicCrystalLattice(Giantstructure)

a. In an ionic compound, constituent ions are held in fixed positions in an orderlyarrangementbystrongelectrostaticforces(orionicbonds).

b. This type of bonding is essentially nondirectional; ions arrange themselves in sites to

form a crystal structure that maximizes attractions and minimizes repulsions. Latticestructureconsistingofaregulararrayofpositivelycharged ionsandnegativelychargedions.

c. Theelectrostatic forcesarestrong,giving rise to large latticeenergies it takesa large

quantityofenergytodisruptthecrystal.

d. Variousarrangementsarepossible.Thesodiumchloridecrystallatticeisshownbelow. e. EachClionissurroundedbysixnearestNa+whileeachNa+issurroundedbysixnearest

Cl.ThecoordinationnumberofbothClandNa+issix. f. Thecoordinationnumberisthenumberofnearestneighbours(atoms,ionsormolecules).1.8 PredictLikelyIonicCompound

a. Metalsalmostalwaysformpositiveionsandformioniccompounds.ExceptionincludeBe,Al

b. Nonmetalsgivemonatomicnegativeionsinioniccompoundsonlywhencombinedwith

ametal.

c. ThefurtheraparttwoelementsareinthePeriodicTable,themorelikelytheyaretoformanioniccompoundonreaction.Largedifferenceinelectronegativitybetweenmetalsandnonmetals.

d. Thetotalpositivechargefromthecationsmustbebalancedbythetotalnegativecharge

fromtheanionsnofreeelectronsarefloatingaround.

8

1.9 ConceptofElectronegativity a. According to this concept,eachkindofatomhasa certainattraction for theelectrons

involvedinachemicalbond.Thiselectronattractingpowerofeachatomcanbelistednumericallyonanelectronegativityscale.

MetallicElements NonmetallicElements

Li Be B(1.0) (1.5) (2.0)

C N O F(2.5) (3.0) (3.5) (4.0)

Na Mg Al(1.0) (1.2) (1.5)

Si P S Cl(1.8) (2.1) (2.5) (3.0)

K Ca Sc(0.9) (1.0) (1.3)

Se Br(2.4) (2.8)

b. Fluorine,which has the greatest attraction for electrons in bondforming situations is

assignedthehighestvalueonthisscale.Allotheratomsareassignedvalueslessthanthatoffluorineasshownabove.

c. Electronegativityvaluemeasuresthepowerofanatominamoleculetoattractelectrons

toitself. d. Notethefollowingtrends: i. Metalsgenerallyhavelowelectronegativityvalues,whilenonmetalshaverelatively

highelectronegativityvalues. ii. Electronegativity values generally increase from left to right within the Periodic

Tableoftheelements. iii. Electronegativityvaluesgenerallydecreasefromtoptobottomwithineachfamilyof

elementswithinthePeriodicTable.1.10 IonicBondandCoulombsLaw(Enrichment)

a. Coulombs Law isused to calculate theenergy in forming the ionpair. It says that theenergyofinteractionoftwoionsisdirectlyproportionaltotheproductoftheirelectricalchargesandisinverselyproportionaltothedistancebetweentheircentres.

2

+ -

r

(q x q )Attractive force F = k whereconstantk=9x109Nm2/C2, q+andqarechargesontheionsandrisdistancebetweenthecentresofthetwoions.b. Theforceofattractionbetweenoppositelycharged ions increasesasthechargesonthe

ionsbecome largerandas thedistancebetween the ionsbecomessmaller.Operate inanydirection.

9

1.11 PhysicalPropertiesofIonicCompounds

a. Highmeltingpointsandboilingpoints(lowvolatility).Alargeamountofenergyisneededtoovercometheelectrostaticforcebetweenoppositelychargedionsformeltingorboiling.Manyioniccompoundshavemeltingpointsgreaterthan500oCandallaresolidsatroomtemperature.

Na2O MgO Al2O3 NaCl MgCl2920oC 2800oC 2045oC 801oC 712oC

Note:Ionicbondstrengthisproportionaltotheioniccharge/size Useasrefractorymaterials(heatresistant)

e.g.MgOusedtolinetheinteriorofblastfurnaces e.g.Al2O3usedtomakecruciblesandsparkplugsformotorcars

b. Usually soluble inpolar solvente.g.waterbut insoluble innonpolar solvents. Insoluble

onesincludeAgCl,MgO,CaCO3.

c. Conductelectricalcurrentinmoltenorsolution(aqueous)statebutnotinthesolidstate.

In the solid state, the ionsareheld in fixedpositionsand cannotactasmobile chargecarriers. In themoltenoraqueous state, theelectrostatic forcesareovercomeand theionsbecomemobile.Inconductingelectricity,themoltenoraqueousioniccompoundsaredecomposedbytheelectriccurrentelectrolysis.Note:Afewnonionicsubstancesreactwithwatertoformmobileionse.g.PCl3andHCl

d. Hardandbrittle.

A slight displacement along a cleavage plane by a sharp hard blow brings ions of likecharges opposite one another. Strong attraction between planes becomes strongrepulsionandtheioniccrystalshatters.

10

2. METALLICBONDING2.1 NatureofMetallicBonding

a. A metal is an orderly crystalline packing of positive ions, each one having given upelectronsfromitsoutermost,incompleteelectronshell.Theseelectrons,insteadofbeingconfinedtothevicinityofoneatomasinagas,arecompletelydelocalisedandarefreetowanderfromoneendofthemetaltotheother.

Metalscanbeconsideredtobecomposedofarigidlatticeofpositiveionssurroundedbyaseaofelectrons.

b. Strongelectrostatic attractionbetween thepositive ions and adiffuse cloudofmobile

electronsresultinanorderedarrangementinwhichtheionsarecloselypacked.Withoutthem,thefullforceofelectrostaticrepulsionbetweenpositiveionswouldblowthemetalapart.Withthem,thepositiveionscanbepackedtogetherlikemarblesinabox.

c. Thefree/conductionelectronsaresaidtoformaseaofelectrons.2.2 PhysicalPropertiesofMetals

a. HighelectricalconductivityeveninthesolidstateConduct electricity in solidormolten and arenot changed in the process.Delocalisedelectronscanmoveundertheinfluenceofelectricfield.

b. Usuallyhighmeltingandboilingpoints Ahightemperatureisneededtomeltorboilmetalssincemetallicbondsarestrong. Themeltingpointincreasesasthebondstrengthincreases. Thebondstrengthisdependentonthenumberofelectronsinvolvedinformingthebond.c. Malleableandductile

Themetallicbondisnondirectional.Alayerofpositiveionscanslideoveranothereasilywithoutbreakingthemetallicbond.Thusametalcanbeneateninshape(malleable)anddrawnintoawire(ductile).