Download Module 8: Descriptive Chemistry

Reactionsofalkalimetals
• Withhalogens(F2,Cl2,Br2,I2):
– M+X2 à MX
• Withhydrogen:
– M+H2 à MH
• With(excess)oxygen:
– Li+O2 à Li2O(plussomeLi2O2)
– Na+O2 à Na2O2 (plussomeNa2O)
– M+O2 à MO2 (M=K,Rb,Cs)
• Withwater:
– M+H2Oà MOH+H2
Reactionsofalkalineearthmetals
• Withhalogens(F2,Cl2,Br2,I2):
– M+X2 à MX2
• Withnitrogen:
– M+N2 à M3N2
• Withoxygen:
– M+O2 à MO
• Withwater:
– Mg+H2O(g)à MgO +H2
– M+H2Oà M(OH)2 +H2 (M≠Mg)
PeriodicTrends
• Patternsthatemergeinchemicalandphysicalpropertieswhen
elementsarearrangedintheperiodictable
• Canusuallybeexplainedbythenumberofvalenceelectrons,
thenumberofcoreelectrons,andthenumberofprotons
(nuclearcharge)
AtomicRadius
• Generallyatomicradiusdecreasesacrossaperiodand
increasesdownagroup
– Thetrendonlyworksformaingroupelements
http://edtech2.boisestate.edu/kilnerr/502/jigsaw.html
IonizationEnergy
• Generallydecreases asyougodownagroup
– Outermostelectronsare(onaverage)further awayfrom thenucleus, sothereis
agreatershielding effect
• Generallyincreasesasyougoacrossaperiod
– Elementshaveagreatertendencytogainelectrons(ratherthanlose)
• Minoreffects canbedueto
– whatsubshell theelectronisin(s>p>d>f becauseofenergy)
– Pairedvs.unpaired electrons(unpaired>paired becauseofrepulsions)
Overview- PeriodicTrendsinGroup13
• Bisanonmetal/metalloid– formscovalentbondsbutdisplays
electricalpropertiesofsemiconductors(diagonalrelationship
withSi)
• Alisametal/metalloid–formscovalentbondsbutcanalsolose
valenceelectronstoformions(Al3+)
• Ga – formsGa3+ ionstoachievestableconfiguration([Ar]3d10)
• InandTl tendtoform+1ionsbecausetheylosethevalencep
electronbutNOTthevalenceselectrons(inertpair)
Diagonalrelationships
• Oftenthe1st memberofagrouphas
propertiesthataredifferentfrom
theothermembersofthegroup,
butaresimilartothoseofthe2nd
memberoftheadjacentgroup
– Relativelyhighchargedensity
• Example:Li
• Li2CO3,LiF,LiOH andLi3PO4 are
muchlesssolublethanthe
correspondingsaltsoftheother
alkalimetals
– Li2CO3 andLiOH formLi2O
• Li+N2 à Li3N(otheralkalimetals
don’treact)
• Li+O2 à Li2O(otheralkalimetals
formperoxidesorsuperoxides)
Hydrogen
• Makesup<1%ofthemassoftheEarth’scrust,butabout90%ofthe
atomsintheSunandouterspace
• Canbeformedviareactionsthattypicallyrequirehightemperatures
(1000oC)andacatalyst
– Water-gasreaction:C(s)+H2O(g)à CO(g)+H2(g)
– Water-gasshiftreaction:CO(g)+H2O(g)à CO2(g)+H2(g)
– Reformingofmethane(butinprincipleanyhydrocarbon):CH4(g)+H2O(g)
à CO(g)+3H2(g)
• Principalcommercialsourceofhydrogen
– Catalyticreforming:C6H14 à C6H6 +4H2
Usesforhydrogen
• About½oftheH2 manufacturedisusedtomakeNH3 (Haber
process),whichcanbeusedtofertilizers,plasticsand
explosives.
• Asignificantamountisalsousedinthepetrochemicalindustry
– Hydrogenationofunsaturatedcompounds:C6H6 +H2 à C6H12
– Synthesisofmethanol:CO+H2 à CH3OH
• Metallurgy:WO3 +H2 à W+H2O
Carboncompounds(inorganic)
• Reactionwithmetals(oxides)toformcarbides(acetylides)athigh
temperatures:
– CaO(s)+3C(s)à CaC2(s)+CO(g)
– CaC2(s)+2H2O(l)à Ca(OH)2(s)+C2H2(g)
• Methanecanbeconvertedtoinorganiccompounds:
– CH4 +4Sà CS2 +2H2S
– CH4 +4Cl2 à CCl4 +4HCl
• CN- reactsmuchlikeahalide:
– Dimerizationtocyanogen(CN)2
– Disproportionationinbasicsolution:(CN)2 +2OH- à CN- +OCN- +H2O
Siliconcompounds
• Siisthe2nd mostabundantelementintheEarth’scrust(afterO)
• Sicanmakefourbonds,butisincapableofmakingextended
systemslikeCcan
– SiissignificantlylargerthanC
– Si-SiandSi-Hbondsarerelativelyweak
• Sicrystallizesinacubicarrangementsimilartodiamond
(tetrahedral,sp3 hybridized)
– Can’tformπ bondssocannotformsheetsthewaygraphitecan(porbitals
aretoolargeforefficientoverlap)
Silicaandsilicates
• SiO2 isreallyanetworkcovalent
solidwhereeachSiatomsis
bondedto4Oatoms,andeach
Oatomisbondedto2Siatoms
• SiO44- andSi2O76- canarrange
tetrahedrally withcations to
formminerals(ex.Th4+,Zr4+,
Sc3+)
http://www.edulabworld.com/product/265-sio2-crystal-model-31046-1-d1a7/
Nitrogencompounds
• AmmoniacanbesynthesizedbytheHaberprocess:N2 +H2 à NH3
– Generallyusedtomakefertilizer:
NH3 +H2SO4 à (NH4)2SO4
NH3 +H3PO4 à NH4H2PO4 +(NH4)2HPO4
– CanbeconvertedtoNOusingtheOstwaldreaction,whichcanthenform
nitricacid:
4NH3 +5O2 à 4NO+6H2O
2NO+O2 à 2NO2
3NO2 +H2Oà 2HNO3 +NO
Propertiesofoxygen
• MostabundantsubstanceinEarth’scrust
• CanformcompoundswithallelementsexceptHe,NeandAr
• Generallyhasanoxidationnumberof-2incompounds(oxide),
butitcanalsobe-1(O22-,peroxide)or-1/2(O2-,superoxide)
• CanexistasO2 orO3
• O3 isastrongoxidizingagent(acidicsolutions):
O3 +2H+ +2e- à O2 +H2O Eo =2.075V
Synthesisofoxygen
• Generallymadebydecompositionreactions:
HgO à Hg+O2
KClO3 à KCl +O2
H2O2 à H2O+O2
• Reactioninvolvingsuperoxide:
KO2 +CO2 à K2CO3 +O2
• Canalsobemadebyelectrolysis:
H2Oà H2 +O2
Compoundswithfluorine
• FluorinereactswitheveryelementexceptHeandNe
• ReactionwithUallowsforseparationofU-235andU-238isotopesby
gaseousdiffusion:
U+F2 à UF6
• ReactionwithSformsagaseouselectricalinsulator:
S+F2 à SF6
• HFcanbesynthesizedfromafluorideandconcentratedsulfuricacid:
CaF2 +H2SO4 à CaSO4 +HF
• HFcanbeusedforetching:
SiO2 +HFà H2O+SiF4
Compoundswithchlorine
• Chlorinereactswithhydrocarbons:
– Ex.CH4 +Cl2 à CH3Cl+CH2Cl2 +CHCl3 +CCl4
• Chlorofluorocarbons(CFCs)arevolatileliquidsthatare
commonlyusedasrefrigerants,althoughtheyareknownto
damagetheozonelayer
– Ex.CFCl3 andCF2Cl2
• HCl canbesynthesizedfromachlorideandconcentrated
sulfuricacid:
NaCl +H2SO4 à Na2SO4 +HCl
Interestingfactsaboutthed-blockelements
• Inthe4th period,Cu2+istheonlydivalentcation thathasapositivereduction
potential
– Cu2++2e- à Cu Eo =0.340V
• Inthe4th period,Sc istheonlymetalreactiveenoughtoreactwithwaterand
displacehydrogen
– Sc +H2Oà Sc3++H2
• Goingfromtoptobottom,thenumberofoxidationstatesgenerallyincreases
– Astheoxidationnumberincreases,thecovalentnatureofthecompoundalsoincreases
• Sc andCrhydoxides areamphoteric:
– Sc(OH)3 +H+ à Sc3+
Sc(OH)3 +OH- à Sc(OH)63– Cr(OH)3 +H+ à Cr(H2O)63+Cr(OH)3 +OH- à Cr(OH)4-
Periodictrends– atomicradius
• Going from lefttoright,atomic
radiusdecreases,thenincreases
– greater attractionbetween nucleus
andinner e-sthengreater repulsion
betweeninner e-s
• Going from toptobottom, atomic
radiusincreasesthenstays
approximatelyconstant(oreven
decreasesslightly)
– Greater numberofenergylevels
(shells),butthenlanthanide
contractionoccurssincethe6th period
contains4forbitals,whicharenot
verygoodatscreening (shielding)
valence e-sfromthenucleus
http://gwapchem.wikispaces.com/23.7+Transition+Metals
Lanthanide(rare-earth)metals
• f-blockelements
• Insertedbetweend-blockelements
• Verysimilarpropertiestoeachotherandto3Bmetals
– Difficulttoseparateandisolate
• Ce4++e- à Ce3+hasagreaterEo thanforreductionsinvolving
Cr2O72- orMnO4-
Magneticpropertiesofmetals
• Mostd-blockmetalsareparamagneticbecausetheyhave
unpaireddelectrons
– Individualmagneticmomentsthatcan(temporarily)aligninthe
presenceofanexternalfield
• Fe,CoandNiarealsoferromagnetic
– Domainsthatcan(permanently)aligninthepresenceofanexternal
field,evenafterthefieldisremoved!
– Requirescertaininteratomicdistances
– Canalsooccurinalloys(Al-Cu-Mn,Ag-Al-Mn,andBi-Mn)
PropertiesofFe,CoandNi
• Fecanform+2or+3ionswith[Ar]3d6 and[Ar]3d5 electron
configurations(particularlystable)
• CoandNiformprimarily+2ions([Ar]3d7 and[Ar]3d8,
respectively)
– Cocanhaveanoxidationnumberof+3incomplexionssuchas
[Co(NH3)6]3+
PropertiesofCu,AgandAu
• Relativelyunreactive(filleddorbitals)
– DonotdisplaceH2 fromH+ solutions(butcanreacttoformSO2 or
NOx byreactingwithH2SO4 orHNO3)
• Highestelectricalandthermalconductivitiesofallthemetals
• AudoesnotreactwithanysingleacidtoformH+,butitdoes
withaquaregia (1:3HNO3:HCl):
Au+4H+ +NO3- +4Cl- à [AuCl4]- +2H2O+NO
• Auisresistanttooxidation,whileAgcantarnish(Ag2S)andCu
cancorrode(Cu2(OH)2CO3)
Organiccompounds
• C,H,N,O– about95%ofEarth’slivingthings
• C,H,N,O,P,S– about99%
• Carbonisking!
– 4covalentbonds(withitselforotherelements)
– Optimumsizeandvalence
• Functionalgroup
– Collectionofcertainatomsthatconfercharacteristicchemical(and
biological)activities
Hydrocarbons- alkanes
• Simplestorganicmolecules
• Saturated
• GeneralformulaCnH2n+2
ConstitutionalIsomers
• Samechemicalformula,differentstructural
formula
• LeadstoENORMOUSdiversity
FunctionalGroups
Functional Group
Alkene
Alkyne
AromaticRing(arene)
Halide(X=F,Cl, Br,I)
Alcohol
Ether
Structure
FunctionalGroups
Functional Group
Amine
Aldehyde
Ketone
Carboxylic Acid
Ester
Amide
Structure