Standard/ Class/ Grade - 10 SSC, CBSE; - 8 ICSE Carbon Compounds

Gurudatta K Wagh

Standard 10 Chapter 9 Carbon Compounds

Contents

HydrocarbonsSaturated and unsaturatedCatenationStraight chain and branched chainFunctional groupsHomologous seriesNomenclatureChemical propertiesReactionsSoaps and detergents

Standard 10 Chapter 9 Carbon Compounds

Organic compounds

Compounds directly or indirectly obtained from plants

and animals

Organic chemistry is also known as the chemistry of

carbon compounds

Inorganic compounds Compounds obtained from minerals

Urea CO(NH2)2 , an organic

compound, was synthesized from

an inorganic compound

ammonium cyanate NH4(NCO)

by Friedrich Wohler, a German

chemist

Hydrocarbons

Hydrocarbons (Parent compounds/ fundamental

organic compounds)

All organic compounds contain hydrogen along with

carbon

Some organic compounds also contain oxygen,

halogens, and sometimes nitrogen and sulphur

Methane (marsh gas) CH4

In methane C is bonded to four H atoms

Electronic configuration - C (2, 4), H 1 C has four electrons in its outermost orbit – tetravalentIf C gets four electrons in the second orbit, its outermost orbit will be completely filled and will make it stable to attain the nearest inert gas configuration [Neon (2, 8)]

Covalent bond in methane

• C gets four electrons by sharing one electron with

each H atom

• C-H bonds are formed. C atom is centrally placed

• Bonds formed by sharing of electrons are known

as covalent bonds

• A single covalent bond is formed by sharing of two

electrons

Structure

Electron dot and cross structure

If the electrons of C are shown as "x" and the

electrons of H as ". ", then methane appears as

methane

Properties of organic compounds with covalent

bonds

(1) Low melting point and boiling point

(2) Generally insoluble in water but are soluble in

other organic solvents

(3) Poor conductors of heat and electricity

Covalent bond in oxygen

The atomic number of

oxygen is 8

Six electrons are present in

its outermost shell

It requires 2 more electrons

to complete its octet

Each oxygen atom shares its valence electron with the valence electron of another oxygen atom to give two shared pairs of electrons which results in the formation of O2 molecule

If two electron pairs are shared between two atoms, then a double covalent bond (=) is formed

StructureO::O or O = O or O2

Saturated and unsaturated hydrocarbons

Saturated hydrocarbons Carbon atoms are linked to each other only by single bonds

Unsaturated hydrocarbons Hydrocarbons in which carbon atoms are linked to each other by double or triple bonds are known as unsaturated hydrocarbons

Name BondAlkanes Single C-C bondsAlkenes Double C=C bondsAlkynes Triple C≡C

Saturated and unsaturated hydrocarbons can form straight chains or closed chain structures

These chains can have branches and cross links and are known as closed chain or ring compounds

Catenation The remarkable property of carbon atom

to form bonds with itself and give rise to a single

large structure or chain

Definition: The property of direct bonding between

atoms of same element to form a chain

The carbon chains can be straight or branched

forming large molecules

Allotropes of Carbon

Allotropy

The phenomenon of existence of a substance in

various physical forms but same chemical form

Diamond and graphiteBoth are formed by carbon atoms

Diamond Graphitehard, beautiful, crystalline soft, grayish black,

crystallineEach carbon atom is linked to four other neighbouring, carbon atoms held at the corners of a regular tetrahedron by covalent bonds to form a rigid three dimensional structure

Each carbon atom is attached to three other carbon atoms forming a hexagonal planar structure

Physical properties of graphite and diamond are different but their chemical properties are the same

Diamond GraphiteThere are no mobile electrons in the system and hence diamond crystal is a non-conductor of electricity

Free electrons move throughout the entire layers, and hence graphite is a good conductor of electricity

Used as precious stone in jewellery.Black diamonds are used for cutting glass

Used in making electrodes and carbon, lubricants and lead pencils

Parent hydrocarbons

Methane CH4 is a saturated hydrocarbon and an alkane

If we increase the number of carbon atoms by 1 and the number of hydrogen atoms by 2, then we get ethane C2H6 and is the next member in the family of alkanes

If we add one more carbon atom and two more hydrogen atoms to ethane, we get propane C3H8

The general formula for alkanes is CnH2n+2 where n is the number of carbon atoms

Isomers and isomerism

Compounds with identical molecular formula but

different structure hence called isomers and the

property is known as isomerism

Straight chain and branched chain

Pentane C5H12

Three possible carbon skeletons

The carbon atoms are linked together in the form of

open chainThese compounds also contain branched chain

Pentane C5H12

Three possible carbon skeletons

Pentane C5H12

Closed ring Cyclohexane C6H12

The two ends of a chain of carbon atoms are joined

together

Structure of Benzene C6H6 Benzene ring is made up

of six carbon atoms, in which each carbon atom is

joined by a single bond on one side and double bond

on other side (alternate single bond and double

bonds)

Functional groups in organic compounds

All organic compounds are considered as the

derivatives of hydrocarbons

The derivatives are formed by replacing one or more

hydrogen atoms in a molecule of hydrocarbon by

some other atom or group of atoms

After replacement, a new set of compounds is formed

which has functions (properties) different from the

parent hydrocarbon

Functional group

It is the atom or group of atoms present in the

molecule which determines characteristics property

of organic compounds

If one hydrogen in methane CH4 is replaced by an

-OH group, then a compound known as methyl

alcohol CH3OH is formed

The -OH group is known as the alcoholic functional

group

Type General formulaR = CnH2n+1

R = alkyl group

Functional group

Compound containing functional groupName Formula

Alcohols R-OH -OH Ethyl alcohol C2H5OH

Aldehydes R-CHO 1) Acetaldehyde 2)

Ketones 3)  4) Acetone (Dimethyl ketone)

5)

Carboxylic acid R-COOH -COOH Acetic acid CH3COOH

1) aldehyde 2) acetaldehyde 3) ketone 4) carbonyl group

5) acetone

Homologous series A group of organic compounds

containing same functional group, which can be

represented by the same general formula and which

more or less show similar trends in their properties

Some important characteristics of homologous

series

(1)The general formula of all compounds in the series

is the same (2) They have the same functional group

(3) Physical properties like melting point, boiling point,

density, generally show a gradual change with increase of

molecular formula in the series. On the other hand,

chemical properties of the member show close

resemblance because of the presence of the same

functional group in them

(4) Consecutive members of the series differ from one

another by -CH2- group which is known as the methylene

group and their molecular weight differs by 14 units

1. Alkanes The Alkane family is a homologous series and characterized by the general formula CnH2n+2

Methane CH4

Ethane C2H6

Differ by –CH2 units

Ethane C2H6

Propane C3H8

Differ by –CH2 units

Butane C4H10

Pentane C5H12

Differ by –CH2 units

2. Alcohols CnH2n+1OH

Methyl alcohol CH3OHEthyl alcohol C2H5OH

Differ by –CH2 units

Propyl alcohol C3H7OH Butyl alcohol C4H9OH

Differ by –CH2 units

Nomenclature of organic compounds IUPAC (lnternational Union of Pure and Applied Chemists)

system is the latest and widely accepted system for giving

systematic names to organic compounds

All organic compounds are considered as derivatives of

saturated hydrocarbons and are known as Alkanes

To express the name of the compound the basic carbon chain

is modified by 'root'. A root indicates the “nature of basic carbon

skeleton”, prefix indicates “phrase before” and suffix indicates

“phrase after”

Terminology used in nomenclatureRoot: It indicates the nature and the number of carbon atoms in the basic carbon skeleton

Bond with Root wordOne C atom Meth-Two C atom Eth-Three C atom Prop-Four C atom But-Five C atom Pent-Six C atom Hex-Seven C atom Hept-Eight C atom Oct-

Suffix: It denotes the type of bonds or functional group present in the carbon chain. A Suffix is added to a root word to indicate the saturation or unsaturation in the carbon chain

C chain Suffix Root nameSaturated –C–C- -ane AlkaneUnsaturated –C=C-

-ene Alkene

Unsaturated -C≡C-

-yne Alkyne

Prefix: It indicates the presence of other functional groups and their position

Examples

Ethanol C2H5OH

One hydrogen atom is substituted by the -OH group

Select the longest chain of carbon atoms

The name of the parent alkane is ethane

Since the functional group is alcohol, remove the ‘e’

from the word ethane and substitute it with ‘ol’ ('ol'

stands for alcohol) The carbon atom to which the -OH group is attached is numbered as C1 and the other carbon atoms are numbered accordingly The compound C2H5OH is named as ethan-1-ol indicating that the functional group-OH is attached to the carbon atom at the end of the chain

2-bromopropane 1-bromopropane

• One hydrogen atom in the chain is substituted by

-Br group

• The longest chain is of three carbon atoms• The name of the parent alkane is propane• The functional group is halide (in this case bromo) • The carbon atom nearest to the substituted group is

numbered as C1 and C2, respectively • The compounds are called 2-bromopropane

and 1-bromopropane, respectively

Unsaturated compound containing a double bond

CH2=CH2

CH2=CH-CH3

CH2=CH-CH2-CH3

CH3-CH=CH-CH3

Ethene (ethylene)

Propene

Butene-1

Butene-2

CH3CH2CH=CH2

4 3 2 1 The longest chain of carbon atoms is four The parent alkane is butane. The above chain is

named as butene In the structure, the numbering of carbon atoms starts

from the carbon atom nearest to the double bond. In the above case, the carbon atom on the extreme right is numbered 1

The position of the double bond in the chain is indicated by prefix the lower number of the carbon atoms between the double bonds. In the above case, since the double bond is between C1 and C2, the compound is known as but-1-ene

Unsaturated compound containing a triple bond H-C≡C-H ethyne/ acetyleneThe same rules as for double bonds are followed. The suffix is changed from -ene- to -yne-

Chemical properties of carbon compounds

Combustion All hydrocarbons burn in air or oxygen

to form CO2 and H20

The reactions are exothermic with the evolution of a

large amount of heat

(1) CH4(g) + 2O2(g) → CO2(g) + 2H2O (g) + Heat and light

(2) 2C4H10(g) + 13O2(g) exothermic 8CO2(g) + 10H2O(l) + 2658 KJ Heat combustion

If very limited air is supplied, then methane gives carbon

black CH4 + O2 → C + 2H20 limited air → carbon black

Saturated hydrocarbons give a clean flame (oxidizing

flame) but when unsaturated carbon compounds burn,

they give a yellow flame (reducing flame) with lots of

black carbon

When gas or kerosene stove is used a sufficient quantity

of air is used and hence we get clean blue flame

Addition Reaction The reaction in which two molecules react to form a single product is known as addition reaction. This type of reaction occurs only in unsaturated compounds where there are double or triple bonds.

(a) Reactant adds to the carbon atoms of C=C double and C≡C triple bond

ethene + bromine → ethylene dibromide

(b) Addition of hydrogen molecule to ethene gives corresponding ethane i.e. saturated product (unsaturated compound gets converted into saturated compound)

Substitution Reaction

Reactions where substitution of one (or more atoms)

in a molecule for another atom takes place are called

substitution reactions

CH4 + Cl2 UV rays CH3Cl + HCl (H substituted by Cl)

CH3CH2I + KOH → CH3CH20H + KI (I substituted by OH)

Some important carbon compounds

EthanolEthanol C2H5OH is called ethyl alcohol or spirit, has a linear structure CH3CH2OH. It is a colourless liquid and has a pleasant odour. Boiling point is 78 °C and freezing point is -114 °C. It is combustible and burns with blue flame

Reactions with ethyl alcohol (a) When sodium comes in contact with ethyl alcohol it gives hydrogen gas

2C2H5OH + 2Na → 2C2H5ONa + H2

(ethyl alcohol + sodium → sodium ethoxide + gas)

(b) When ethyl alcohol reacts with PCI3 it forms ethyl chloride

3C2H5OH + PCI3 → 3C2H5Cl + H3PO3

(ethyl alcohol + phosphorous trichloride → ethyl chloride + phosphorous acid)

Reactions with ethanoic acid (acetic acid) C2H4O2

Has a linear structure CH3COOH, is a weak acid, colourless, corrosive liquid and has pungent smell at ordinary temperature. Below 290 K it solidifies to an ice like mass called glacial acetic acid

(a) Reaction with halogens

When acetic acid reacts with chlorine gives monochloroacetic acid

CH3COOH + Cl2 → CH2CICOOH + HCI Monochloroacetic acid

CH2CICOOH + Cl2 → CHCI2COOH + HCI Dichloroacetic acid CHCI2COOH + Cl2 → CCl3COOH + HCI Trichloroacetic acid

(b) Reaction with metals

When acetic acid reacts with Na or Zn it gives sodium acetate with liberation of Hydrogen gas

2CH3COOH + 2Na → 2CH3COONa + H2

(c) Reaction with alcohol

When acetic acid reacts with ethyl alcohol in presence of anhydrous ZnCl2, ethyl acetate is formed CH3COOH + C2H5OH → CH3COOC2H5 + H2O

Soaps and Detergents

• Soaps are cleansing agents which are capable of reacting with water to dislodge the unwanted particles from cloth or skin

• The molecules of soap are sodium or potassium salts of long chain carboxylic acids

• A soap molecule has a tadpole shaped structure

• At one end (long non polar end) of soap molecule is a hydrocarbon chain i.e. insoluble in water but soluble in oil

• At the other end (short polar end) of soap molecule there is a carboxylate ion which is hydrophilic i.e. water soluble but insoluble in oil

• When soap is mixed with water, the solution becomes concentrated and causes foaming

• The long non-polar end of soap gravitates towards and surrounds the dirt and absorbs the dust in it

• The short polar end with the carboxylate ion turns the water away from the dirt

• The soap molecule thus helps in dissolving the dirt in water and we can wash our clothes clean

Toilet soap Laundry soap High quality of fats used for raw material

Cheaper quality of oils and fats are used

Expensive perfumes added

Cheaper perfumes added

No free alkali content present to prevent injuries to skin

Free alkali present for cleaning action

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