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CBSEClass10Science

RevisionNotes

CHAPTER–4

CARBONANDITSCOMPOUNDS

Carbonisaversatileelement.Foundin.02%informofmineralsan03%informof

Alllivingstructuresarecarbonbased.

CovalentBondinCarbon

Theatomicnumberofcarbonis6anditselectronicconfigurationis2,4.Toattaina

noblegasconfigurationitrequiresfourmoreelectronsinitsvalenceshell.

Itisdifficultforanatomofcarbontoeithergainorloseelectronsasitwouldbe

difficulttoholdextraelectronsandwouldrequirealargeamountofenergyto

removefourelectrons.

Carbonattainsthenoblegasconfigurationbysharingitsvalenceelectronswithother

atoms.Suchmutualsharingofelectronsbetweenatomstoattainastablenoblegas

configurationiscalledCovalentbonding.

Atomsofotherelementslikehydrogen,oxygen,nitrogen,chlorinealsoshowsharing

ofvalenceelectrons.

Dependingonthenumberofelectronpairsshared,covalentbondisofthreetypes:

1. SingleCovalentBond:Singlecovalentbondisformedbecauseofsharingoftwo

electrons,i.eonepair.Example:Hydrogen,Chlorine,Methane.

2. Doublecovalentbond:Doublebondisformedbysharingoffourelectrons,i.etwopairs

ofelectrons.Example:Oxygenmolecule,CarbonDioxidemolecule.

3. TripleCovalentBond:Triplecovalentbondisformedbecauseofthesharingofsix

electrons,threepairsofelectrons.Example:Nitrogen,C2H2

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PropertiesofCovalentBonds.

– Covalentlybondedmoleculeshavelowmeltingandboilingpoints.

--comparativelyweakerintermolecularforces,unlikeioniccompounds.

– Thesemoleculesaregenerallypoorconductorofelectricitysincenochargedparticlesare

formed.

Twoimportantpropertieswhichenablecarbontoformenormouslylargenumberof

compounds.

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1. CATENATIONispropertyofcarbonatomtoformbondwithotheratomsofcarbon.Like

carbon,siliconformscompoundswithhydrogenuptosevenoreightatomsofsiliconcalled

silanes.

2.TETRAVALENCY:Havingavalencyof4,carbonatomiscapableofbondingwith

atomsofoxygen,hydrogen,nitrogen,sulphur,chlorineandotherelements.Sinceitrequires

fourelectrons,carbonissaidtobetetravalent.

Thesmallersizeofcarbonatomenablesnucleustoholdthesharedpairofelectrons

strongly,thuscarboncompoundsareverystableingeneral.

HYDROCARBONS:Thecompoundswhicharemajorlymadeofhydrogenandcarbon

atoms.Hydrocarbonsarefurtherclassifiedas

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SaturatedandUnsaturatedCarbonCompounds

SaturatedCompounds:Saturatedcompoundsarehydrocarbonsinwhichhydrogenand

carbonhavesinglebonds.TheyarealsoknownasAlkanes.

ALKANE:

UnsaturatedCompounds:hydrocarbonsinwhichhydrogenandcarbonhavedoubleor

triplebonds.hydrocarbonswithdoublecovalentbondsarealkenesandthosewithtriple

covalentbondsarealkynes.

ALKENE:

Note:alkenedoesnotexistwithonecarbonatom,thus,methenedoesnotexist.

ALKYNE:

note:minimumtwocarbonatomsarerequiredtoformalkyne.

Apartfrombranchedstructures,carboncompoundsarepresentincyclicform.Example:

ElectronDotstructure:Lewisstructures(\electrondotstructures)arediagramsthatshow

thebondingbetweenatomsofamoleculeandthelonepairsofelectronsthatmayexistin

themolecule.

StepstodrawaLewisstructure:

1. Decidehowmanyvalence(outershell)electronsarepossessedbyeachatominthe

molecule.

2.Ifthereismorethanoneatomtypeinthemolecule,putthemostmetallicorleast

electronegativeatominthecenter.Recallthatelectro-negativitydecreasesasatommoves

furtherawayfromfluorineontheperiodicchart.

3.Arrangetheelectronssothateachatomcontributesoneelectrontoasinglebondbetween

eachatom.

4.Counttheelectronsaroundeachatom:aretheoctetscomplete?Ifso,yourLewisdot

structureiscomplete.

5. Iftheoctetsareincomplete,andmoreelectronsremaintobeshared,moveoneelectron

perbondperatomtomakeanotherbond.Notethatinsomestructurestherewillbeopen

octets(example:theBofBF3),oratomswhichhavetenelectrons(example:theSofSF5)

6. Repeatsteps4and5asneededuntilalloctetsarefull.

7. Redrawthedotssothatelectronsonanygivenatomareinpairswhereverpossible.

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Electrondotstructureofasaturatedcarboncompound,ethaneisasfollows:

Electrondotstructureofanunsaturatedcarboncompound,etheneisasfollows:

TRYDRAWINGTHEELECTRONDOTSTRUCTUREOFETHYNE

FormulaeandStructuresofSaturatedCompoundsofCarbonandHydrogen

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Onthebasisofstructuresthehydrocarbonscanbe:

Structuralisomers:Thesearethecompoundshavingidenticalmolecularformulabut

differentstructures.Forexample,isomersofbutane.

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NOMENCLATURE:Nomenclatureisthesystemofassignmentofnamesgiventoorganic

compounds.

HeteroatomandFunctionalGroup

Inhydrocarbonchain,oneormorehydrogenatomscanbereplacedbyotheratoms

inaccordancewiththeirvalencies.Theelementthatreplaceshydrogeniscalleda

heteroatom.

Theseheteroatomsandthegroupcontainingthemimpartchemicalpropertiestothe

compoundandhencearecalledfunctionalgroups.

HomologousSeries

Itisaseriesofcompoundsinwhichthesamefunctionalgroupsubstitutesfor

hydrogeninacarbonchain.

Forinstance,theALCOHOLS: OH, , ,

Thesuccessivememberdiffersbyone-CH2unitand14unitsofmass.

Thechemicalpropertiesareimpartedbythefunctionalgroupthusallmembershave

similarchemicalproperties.Butthemembershavedifferentphysicalproperties.

Thephysicalpropertiesvaryamongthemembersofhomologousseriesdueto

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differenceintheirmolecularmass.

Meltingpointandboilingpointincreaseswithincreasingmolecularmass.

Howtonamecarboncompounds:NOMENCLATURE

1. Identifythenumberofcarbonatomsinthecompound.

2. Functionalgroupisindicatedeitherbyprefixorsuffix.

FunctionalGroupSuffixPrefix

Alkene-ene

Alkyn-yne

Alcohol-ol

Aldehyde-al

Ketone-one

Carboxylicacid-oicacid

chlorine-chloro

3. Ifasuffixisadded,thenfinal‘e’isremovedfromthenamee.g.methanol(methane-e=

methan+ol).

ChemicalPropertiesofCarbonCompounds

1. COMBUSTION

Carboncompoundsgenerallyburn(oxidize)inairtoproducecarbondioxideand

water,andreleaseheatandlightenergy.

Saturatedhydrocarbonburnsgenerallywithablueflameingoodsupplyorairand

withayellowsootyflameinlimitedsupplyofair.

Sootyflameisseenwhenunsaturatedhydrocarbonsareburnt.

Burningofcoalandpetroleumemitsoxidesofsulphurandnitrogenwhichare

responsibleforacidrain.

2. OXIDATION:

Alcoholscanbeconvertedtocarboxylicacidsbyoxidizingthemusingalkaline

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potassiumpermanganateoracidifiedpotassiumdi-chromate(theyaddoxygentothe

reactant,thusarecalledoxidizingagents).

3. ADDITIONREACTION

Hydrogenisaddedtounsaturatedhydrocarboninpresenceofpalladiumornickelas

catalyst.

Saturatedfattyacidsareharmfulforhealthandoilswithunsaturatedfatty

Insaturatedhydrocarbons,thehydrogenattachedtocarboncanbereplacedbyanother

atomorgroupofatomsinpresenceofsunlight.

EthanolandEthanoicAcidEthanol

Consumptionofdiluteethanolcausesserioushealthissuesandintakeofpurealcohol

islethal.

CHEMICALPROPERTIESOFETHANOL

reactswithSodiumtoform

SodiumEthoxideandHydrogen

When isheatedwith

concentratedSulphuricAcidat443K.itis

dehydratedtoEthene

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EthanoicAcid(/AceticAcid:

5-8%solutionofaceticacidinwateriscalledvinegar.

Pureaceticacidiscalledglacialaceticacid

REACTSWITH PRODUCTS

1. SODIUMNaSODIUMETHANOATEAND

HYDROGEN

2. SODIUMCARBONATESODIUMETHANOATE,CARBON

DIOXIDEANDWATER

3. SODIUMBICARBONATESODIUMETHANOATE,CARBON

DIOXIDEANDWATER

4.

ETHANOL(INPRESENCEOFCONC.SULPHURIC

ACID) ESTERANDWATER

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5. NAOH SODIUMETHANOATEANDWATER

ethonolofester-ethnoicacid-ethylethanoate

Carboxylicacidsreactwithalcoholsinpresenceoffewdropsofconcentratedsulphuricacid

ascatalystandformsweetsmellingcompoundscalledester.

HydrolysisOnheatingwithanacidorabasetheesterformsbacktheoriginalalcoholand

carboxylicacid.

Alkalinehydrolysisofesterisalsocalledsaponification.

SoapsandDetergents

Soapissodiumandpotassiumsaltofcarboxylicacidswithlongchain.

Soapsareeffectivewithsoftwateronlyandineffectivewithhardwater.

Detergentsareammoniumorsulphonatesaltsofcarboxylicacidswithlongchain.

Theyareeffectivewithbothsoftaswellashardwater.

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Anionicpart(hydrophilic)andalonghydrocarbonchain(hydrophobic)partconstitutesthe

soapmolecule.

Longchainofcarboxylicacid,hydrophobicionicend,hydrophilic

StructureofaSoapmolecule

CleansingActionofSoaps

Mostdirtisoilyinnatureandthehydrophobicendattachesitselfwithdirt,whiletheionic

endissurroundedwithmoleculesofwater.Thisresultinformationofaradialstructure

calledmicelles.

Anemulsionisthusformedbysoapmolecule.Theclothneedstobemechanically

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agitatedtoremovethedirtparticlesfromthecloth.

Scum:Themagnesiumandcalciumsaltspresentinhardwaterreactswithsoap

moleculetoforminsolubleproductscalledscum,thusobstructingthecleansing

action.Useofdetergentsovercomethisproblemasthedetergentmoleculeprevents

theformationofinsolubleproductandthusclothesgetcleaned.

Whatyouhavelearnt

Carbonisaversatileelementthatformsthebasisforalllivingorganismsandmanof

thethingsweuse.

Thislargevarietyofcompoundsisformedbycarbonbecauseofitstetra-valenceand

thepropertyofcatenationthatitexhibits.

Covalentbondsareformedbythesharingofelectronsbetweentwoatomssothat

bothcanachieveacompletelyfilledoutermostshell.

Carbonformscovalentbondswithitselfandotherelementssuchashydrogenoxygen,

sulphur,nitrogenandchlorine.

Carbonalsoformscompoundscontainingdoubleandtriplebondsbetweencarbo-

atoms.Thesecarbonchainsmaybeintheformofstraightchains,branchedchainor

rings.

Theabilityofcarbontoformchainsgivesrisetoahomologousseriesofcompoundin

whichthesamefunctionalgroupisattachedtocarbonchainsofdifferentlengths.

Thefunctionalgroupssuchasalcohols,aldehydes,ketonesandcarboxylicacid

bestowcharacteristicpropertiestothecarboncompoundsthatcontainthem.

Carbonanditscompoundsaresomeofourmajorsourcesoffuels.

Ethanolandethanoicacidarecarboncompoundsofimportanceinourdailylives.

Theactionofsoapsanddetergentsisbasedonthepresenceofbothhydrophobicand

hydrophilicgroupsinthemoleculeandthishelpstoemulsifytheoilydirtandhence

itsremoval.