4.5–MetallicBonding

Understandings• Ametallicbondistheelectrostaticattractionbetweenalatticeofpositiveionsanddelocalizedelectrons.• Thestrengthofametallicbonddependsonthechargeoftheionsandtheradiusofthemetalion.• Alloysusuallycontainmorethanonemetalandhaveenhancedproperties.

ApplicationandSkills• Explanationofelectricalconductivityandmalleabilityinmetals.

• Explanationoftrendsinmeltingpointsofmetals.

Recall•Wherearemetalsfound?

a. sblockb. sandpblocksc. s,p,anddblocksd. s,p,d,fblocks

Recall•Wherearemetalsfound?

a. sblockb. sandpblocksc. s,p,anddblocksd. s,p,d,fblocks

MetallicBonding•Metallicbondsaretheelectrostaticattractionbetweenalattice ofpositiveionsanddelocalizedelectrons.

MetallicBondinginSodium

MetallicBondingStrength• Strengthofmetallicbondincreaseswithchargeofion

HigherMPandBP

MetallicBondingStrength• Strengthofmetallicbondincreaseswithsmaller sizeofion

HigherMPandBP

SodiumandMagnesium• Sodium(Group1)has1delocalizedelectronperatom•Magnesium(Group2)has2delocalizedelectronsperatom

•Magnesiumhasaslightlysmalleratomicradiusthansodium

• Therefore,magnesiumhasstrongermetallicbondingthansodium

MetallicBondingStrength• Determinedby3factors1. thenumberofdelocalizedelectrons2. thechargeonthecation3. theradiusofthecation

Themoredelocalizedelectrons,thehigherthechargeonthecation,thesmaller thecation=strongermetallicbonding

Malleability•Why?

•Metalsaremalleable andductilebecausepositiveionsarefreetoslideovereachotherinaseaofdelocalizedelectrons

GoodElectricalConductivity•Why?

• Forconductivitytooccurthesubstancemustpossesselectronsorionsthatarefreetomove.

•Metals(andgraphite)containdelocalizedelectronsandareexcellentconductors

GoodThermalConductivity•Why?

• Delocalizedelectronsandcloselypackedcationsallowefficienttransferofheatenergy

Alloys• Alloys:metalsmadebycombiningtwoormoremetallicelements

Metals:malleable,closelypackedpositiveionsareallowedtoslideovereachotherthroughaseaofdelocalizedelectrons

Alloys: non-directionalbonding,whichdoesn’tallowatomstoslipunderstress

Alloys• Alloys:metalsmadebycombiningtwoormoremetallicelements

• Thealloyisoftenmorechemicallystable,andalsooftenstrongerandmoreresistanttocorrosionduetonon-directionalbonding.

• Thisisduetodifferentelementshavedifferentsizespreventingtheeasyslidingbetweenatoms.

Steel• Ironwithcarbon andotherelements

• Hightensilestrengthbutcorrodes,usedasstructuralmaterial

SterlingSilver• Silverandcopper• Lustrousbutcorrodes(dependsonpercentageofsilver,themoresilverthelessitcorrodes)• Jewellery,artobjects

Brass• Copperandzinc

• Plumbingfittings,instruments

DECREASING STRENGTHà

Type ofbonding

Covalent Ionic Metallic HydrogenBonding

Dipole-dipoleforces

Londonforces

Cause Twostrongelectronegativeatoms

One strongelectronegativeandoneweakelectronegativeatom

Twoweakelectronegativeatoms

O, NorFfromonemoleculeandahydrogenatomfromanothermolecule

Twopolarmolecules

Twonon-polarmolecules

Strength Bond lengths.Theshorterthebond,thestrongerthebond.

Thesmallertheionsandthegreaterthechargeontheions,thegreatertheattraction.

Themorepositivethenucleus thebetter

Themoreelectronsthebetter

Themorepolarthebetter

Themorepolarthebetter

Moreelectrons

Example Diamond NaCl Cu H2O SO2 CCl4