5 states of matter Alevel考试化学课件.pptx
somelatticestructures
IoniclatticesIonicbondingresultsfromtheelectrostaticattractionsbetweenoppositelychargedionswhichareheldinagiantioniclattice.Thereisaregulararrangementofanionsandcations.Theexactwayinwhichtheindividualionsarearrangeddependsontheirrelativesizesandontherelativecharges.
Asmallrepresentativebitofasodiumchloridelatticelookslikethis:Sodiumchlorideandmagnesiumoxideformacubiclattice,inwhicheachcationissurroundedbysixanionsandeachanionissurroundedbysixcations.
Intheioniclatticetherearestrongelectrostaticattractionsthroughoutthelattice.Thismeansthatmuchenergyisrequiredtoseparatetheionsandthemeltingpointwillbehigh.Theliquidformedcontainsionswhichwillbeattractedtooppositelychargedionspresent;thustheboilingpointwillalsobehigh.ForNaCl,themeltingpointis808℃andtheboiingpointis1456℃ForMgO,themeltingpointis2853℃andtheboilingpointis3600℃
TheotherpropertiesoftheioniccrystalsIoniccrystalsaregenerallystrongandhard,butmayshatterwhenstruckveryhardSolidioniclatticesdonotconductelectricity,butmoltenioniccompoundswill.
Simplemolecularlattices
Simplemolecularlatticeareoftenheldtogetherbyinstantaneousdipole-induceddipoleforces.Thestrengthoftheforceincreaseswiththenumberofelectronspresent.
ElementRelativemolecularmassMeltingpointBoilingpointFluorine38-220-188Chlorine71-101-34Bromine160-758iodine230114183Canyouexplaintheincreasebyyourself?
Thisisbecausethelargemoleculeshavemoreelectronsaroundthem,whichgiverisetolargerinstantaneousdipole-induceddipoleforces.Thusfluorineandchloridearegasesatroomtemperature,bromineisaliquidandiodineisasolid.
Forexample:I2SolidiodinecontainsI2moleculesinwhichthereisacovalentbondbetweentheatoms,butbetweenthemoleculestherearemuchweakerinstantaneousdipole