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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