CHAPTER - 4

CARBON AND ITS

COMPOUNDS
 CARBON
• Carbon belongs to the
group IV of the
periodic table.
• It has four electrons
in its outermost orbit,
so its valency is 4.
• Carbon is a non-
metal.
 Compounds of Carbon are
Widely Distributed in Nature
• The number of carbon
compounds is larger than that
of all other elements put
together.
 Why so many Carbon
Compounds in nature?
• Because carbon is
chemically
unique.
• Only carbon
atoms have the
ability to combine
with themselves
to form long
chains
Occurrence of carbon :-
i) Carbon is found in the
atmosphere, inside the
earth’s crust and in all living
organisms.
ii) Carbon is present in fuels
like wood, coal, charcoal,
coke, petroleum, natural
gas, biogas, marsh gas etc.
Occurrence of carbon :-
iii) Carbon is present in
compounds like carbonates,
hydrogen carbonates etc.
iv) Carbon is found in the
free state as diamond,
graphite, fullerenes etc.
Bonding in carbon Covalent
bond :-
The atomic number of
carbon is 6, its electronic
arrangement is 2,4, it has 4
valence electrons. It can
attain stability by gaining 4
electrons, losing 4 electrons
or sharing 4 electrons with
other atoms.
It does not gain 4 electrons
because it is difficult for the
6 protons to hold 10
electrons.
It does not lose 4 electrons
because it needs a large
amount of energy to lose 4
electrons. So it shares 4
electrons with other atoms
to attain stability resulting in
the formation of covalent
bonds. Since carbon atom
needs 4 electrons to attain
stability, its valency is 4 and
it is tetravalent.
X I
X X
_ _
X
I
C C
Formation of covalent bonds
Covalent bond is chemical
bond formed by the sharing
of electrons between atoms.
The sharing of one pair of
electrons results in the
formation of single covalent
bond, sharing of two pairs
of electrons results in the
formation of double
covalent bond and sharing
of three pairs of electrons
results
in the formation of triple
covalent bond.
E.g.,Formation of single
covalent bond in Hydrogen
molecule - H2
The atomic number of
hydrogen is 1, its electronic
arrangement is 1, it
has 1 valence electron. It
needs 1 electron more to
attain stability. So
two hydrogen atoms share
1 pair of electrons resulting
in the formation of a single
covalent bond in hydrogen
molecule H2.

Hx + xH H XX H H–H H2
Formation of double
covalent bond in oxygen
molecule - O2
atomic number of oxygen is
X

8, its EC is 2,6, it has 6 VE, it

needs 2 electrons more to
attain stability. So two
oxygen atoms share two
pairs of electrons resulting
in the formation of a double
covalent bond in oxygen
molecule O2
Formation of triple covalent
bond in Nitrogen molecule -
N2 - The atomic number of
nitrogen is 7, its EC is 2,5, it
has 5 VE, it needs 3
electrons more to attain
stability. So two nitrogen
atoms share three pairs of
X X XX XX XX
X
O X
X + X O O XX
XX
O O=O O2
XX XX XX XX

X X X X
NΞN
X X XX
N X + XN N XX N N2
X X XX
X X X X
Electron dot structures :-
Methane molecule - CH4 Ethane molecule - C2H6

H H H

X X X
H X
C X
H H X
C X C X
H
X
X X X

H H H

H H H
I I I
H–C–H H –C –C –H
I I I
H H H
Formation of a very large
number of carbon
compounds :-
Carbon forms a very large
number of compounds. The
number of carbon
compounds is more than
three million. It is more than
_

the number of compounds

formed by all other
elements. This is because :-
i) Carbon atom can form
bonds with other carbon
atoms to form long chains,
branched chains and closed
rings. This property is called
catenation.
ii) Since the valency of
carbon is 4, it can form
bonds with other carbon
atoms or with atoms of
other elements like
hydrogen, oxygen,
nitrogen, halogens etc.
Formation of a very large
number of carbon compounds
–C–
I I I I I I I I I I C
–C–C–C–C–C–C– –C–C–C–C– C C
I I I I I I I I I I C C
–C– C
I
Long chain Branched chain Closed ring
Hydrocarbons, Saturated and
Unsaturated hydrocarbons
Hydrocarbons :are
compounds containing
carbon and hydrogen atoms.
i) Saturated hydrocarbons :-
are hydrocarbons having all
single covalent bonds
between the carbon atoms.
Eg : Alkanes :- have all single
covalent bonds between the
carbon atoms and their names
end with – ane.
H
Methane – CH4 H–C–H
H
H H
Ethane – C2H6 H–C–C–H
H H
ii) Unsaturated hydrocarbons:
are hydrocarbons having a
double or triple covalent bond
between two carbon atoms.
Eg : Alkenes and Alkynes.
Alkenes :- have a double
covalent bond between two
carbon atoms. and their names
end with – ene.
H H H H
I I I I
Ethene - C2H4 C=C Propene – C3H6 H–C=C– C–H
I I I I
H H H H
Alkynes :- have a triple
covalent bond between two
carbon atoms and their names
end with – yne.

Ethyne – Ethyne – C2H2H–CΞC–H

H
I
Propyne - C3H4 H–C ΞC–C–H
I
H
Isomerism
Carbon compounds having
the same molecular formula
but different structural
formulae are called isomers.
This property is called
isomerism.
Eg:- Butane – C4H10 has 2
isomers. They are Normal
butane and Iso butane.
 H H H H H H H
I I I I I I I
H–C–C–C–C–H H–C–C–C–H Iso butane
I I I I I I
H H H H H H
H– C –H
Normal butane I
H

Pentane – C5H12 has 3 isomers. They are

Normal pentane, Iso pentane and Neo
pentane. Neo pentane
Iso pentane H
H I
I H– C–H
Normal pentane H–C–H H H
I I
H H H H H H H H H–C– C– C–H
I I I I I I I I I I
H–C–C–C–C–C–H H–C–C–C–C–H H H
I I I I I I I I I H–C–H
H H H H H H H H H I
H
Functional groups :-
An atom or a group of atoms which
decides the properties of a carbon
compound is called a functional
group.
i) Halide( Halo group) :- - Cl, - Br, etc.
( Names end with – ane )
Eg :- CH3Cl – Chloro methane,
C2H5Br – Bromo ethane
ii)Alcohol :-OH( Names end with– ol )
Eg :- CH3OH – Methanol
C2H5OH – Ethanol
 H
iii) Aldehyde :- -CHO - C (Names end with al)
O
Eg :- HCHO – Methanal, CH3CHO – Ethanal
O
II
iv) Carboxylic acid :- - COOH - C - OH
(Names end with – oic acid )
Eg :- HCOOH – Methanoic acid,
CH3COOH – Ethanoic acid
v) Ketone :- - CO – C -(Names end with – one )
II
O
Eg :- CH3COCH3 – Propanone ,
CH3COC2H5 - Butanone
Homologus series :-
Homologus series is a group of
carbon compounds having
similar structures, similar
chemical properties and whose
successive members differ by a
– CH2 group. Eg :- Alkanes,
Alkenes, Alkynes etc.
Alkanes :- have general
molecular formula CnH2n+2 .
Their names end with – ane
and the members are as follows
Methane - CH4 Ethane - C2H6
Propane - C3H8 Butane - C4H10
Pentane - C5H12
H
I
Methane :– CH4 H–C–H
I
H
 H H
I I
Ethane :– C2H6 H–C–C–H
I I
H H
H H H
I I I
Propane – C3H8 H–C–C–C–H
I I I
H H H
Alkenes :-Alkenes have general
molecular formula CnH2n . Their names
end with – ene and the members are
as follows :-
Ethene - C2H4
Propene - C3H6
Butene - C4H8
Pentene - C5H10
H H
I I
Ethene :- C2H4 C=C
I I
H H
 H H H
I I I
Propene :- C3H6 H–C=C–C–H
I
H

H H H H
I I I I
Butene :- C4H8 H–C=C–C–C–H
I I
H H
 Alkynes :-
Alkynes have general molecular formula CnH 2n – 2 .Their names end
with – yne and the members are as follows :-
Ethyne - C 2H 2
Propyne - C3H4
Butyne - C 4H 6

Ethyne :- C2H2 H–C C–H

H
I
Propyne :- C3H4 H – C C–C–H
I
H
H H
I I
Butyne :- C4H6 H – C C–C–C–H
I I
H H
10) Chemical properties of Carbon compounds :-
a) Combustion :-
Carbon compounds burn in oxygen to form water, carbon dioxide,
heat and light.
Eg :- C + O2 CO2 + heat + light
CH4 + 2O2 2H2O + CO2 + heat + light
C2H5OH + 3O2 3H2O + 2CO2 heat + light

b) Oxidation :-
Carbon compounds like alcohols are oxidised to carboxylic acids on
heating with oxidising agents like alkaline Potassium permanganate
– KMnO4 or acidic potassium dichromate - K2Cr2O7 .
Eg:- Alcohols are oxidised to Carboxylic acids
alkaline KMnO4 + heat
C2H5OH CH3COOH
Ethanol acidic K2Cr2O7 + heat Ethanoic acid
c) Addition reaction :-
Unsaturated hydrocarbons undergo addition reaction with hydrogen in the
presence of nickel or palladium as catalyst to form saturated hydrocarbons.
Eg:- Ethene undergoes addition reaction with hydrogen to form ethane in the
presence of nickel or palladium as catalyst.
Ni or Pd catalyst
C2H4 + H2 C2H6
H H H H
I I Ni or Pd catalyst I I
C = C + H2 H–C–C–H
I I I I
H H H H
The addition of hydrogen to unsaturated hydrocarbons to form saturated
hydrocarbons is called hydrogenation. Hydrogenation is used to convert
unsaturated oils and fats to saturated oils and fats.
d) Substitution reaction :-
Saturated hydrocarbons undergo substitution reaction with halogens to
form substitution products.
Eg :- Methane undergoes substitution reaction with chlorine in the presence
of sunlight to form substitution products.
CH4 + Cl2 CH3Cl + HCl CH3Cl + Cl2 CH2Cl2 + HCl
CH2Cl2 + Cl2 CHCI3 + HCl CHCI3 + Cl2 CCl4 + HCl
11) Some important carbon compounds :-
a) ETHANOL :- C2H5OH - Ethyl alcohol
Properties :-
i) Ethanol is a colourless liquid with a pleasant smell and burning
taste.
ii) It is soluble in water.
iii) Ethanol reacts with sodium to form sodium ethoxide and hydrogen.
2C2H5OH + 2Na 2C2H5ONa + H2
iv) Ethanol reacts with hot conc. H2SO4 to form ethene and water. Conc.
H2SO4 is a dehydrating agent and removes water from ethanol.
conc. H2SO4
C2H5OH C 2H 4 + H 2O
Uses :-
i) Ethanol is used for making alcoholic drinks.
ii) It is used as a solvent.
iii) It is used for making medicines like tincture iodine, cough syrups,
tonics etc.
b) ETHANOIC ACID :- CH3COOH – Acetic acid
Properties :-
i) Ethanoic acid is a colourless liquid with a pungent smell and sour taste.
ii) It is soluble in water.
iii) A solution of 5% to 8% ethanoic acid in water is called Vinegar.
iv) Esterification :-
Ethanoic acid reacts with ethanol to form the ester ethyl ethanoate in the presence
of conc. H2SO4.
conc.H2SO4
CH3COOH + C2H5OH CH3COOC2H5 + H2O
The reaction between carboxylic acid and alcohol to form an ester is called
esterification.
v) Saponification :-
When an ester reacts with sodium hydroxide solution, the sodium salt of the
carboxylic acid and the parent alcohol are formed. This reaction is called
saponification.
Eg :-Ethyl ethanoate reacts with sodium hydroxide to form sodium acetate and ethanol.
CH3COOC2H5 + NaOH CH3COONa + C2H5OH
vi) Ethanoic acid reacts with bases to form salt and water.
CH3COOH + NaOH CH3COONa + H2O
vii) Ethanoic acid reacts with carbonates and hydrogen carbonates to form salt, water
and carbon dioxide.
2CH3COOH + Na2CO3 2CH3COONa + H2O + CO2
CH3COOH + NaHCO3 CH3COONa + H2O + CO2
12) Soaps and detergents :-
a) Soaps :- Soaps are long chain sodium or potassium salts of carboxylic
acids. Eg:- Sodium stearate – C17H35COONa
Structure of soap molecule :- A soap molecule has two parts. A long
hydrocarbon part which is hydrophobic (water repelling) and soluble in oil and
grease and a short ionic part which is hydrophyllic (water attracting) and
insoluble in oil and grease.
COO Na
+

Hydrocarbon part Ionic part

(Water repelling) (Water attracting)
Cleansing action of soap :- When soap is dissolved in water it forms
spherical structures called micelles. In each micelle the soap molecules are
arranged radially such that the HC part is towards the centre and the ionic part
is towards the outside. The HC part dissolves the dirt, oil and grease and forms
an emulsion at the centre of the micelles which can be washed away by water.
b) Detergents :-
Detergents are long chain sodium salts of sulphonic acids.
Soaps do not wash well with hard water because it forms insoluble
precipitates of calcium and magnesium salts in hard water.
Detergents wash well with hard water because it does not form insoluble
precipitates of calcium and magnesium salts in hard water.

c) Differences between soaps and detergents :-

Soaps Detergents

i) Soaps are sodium salts of Detergents are sodium salts of

fatty acids. sulphonic acids.
ii) Soaps clean well in soft water but Detergents clean well with both
do not clean well in hard water. hard and soft water.
iii) Soaps do not clean as well as Detergents clean better than soaps.
detergents.
iv) Soaps are biodegradable and Some detergents are non biodegradable
do not cause pollution. and cause pollution.