Carbon and it's compounds_notes PDf note

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CHAPTER 4
CARBON AND ITS COMPOUNDS
The element carbon is of immense significance to us in both its elemental form and in the combined form.
Food, clothes, medicines, books, plastics, petroleum products or many of the things that we use or
consume in daily life are all based on this versatile element carbon. In addition, all living structures are
carbon based.
Carbon in the given compound can be detected by burning the compound in air and passing the liberated
CO2 gas through lime water which turns milky due to the formation of white precipitate of CaCO3.
The amount of carbon present in the earth’s crust and in the atmosphere is quite less. The earth’s crust has
only 0.02% carbon in the form of minerals (like carbonates, hydrogen carbonates, coal and petroleum) and
the atmosphere has 0.03% of carbon dioxide. In spite of this small amount of carbon available in nature,
we see a large number of carbon compounds around us. This anomalous behaviour of carbon can be
explained based on its unique properties.
BONDING IN CARBON COMPOUNDS – THE COVALENT BOND:
✓ Ionic compounds have high melting and boiling points and conduct electricity in solution or in the
molten state. The nature of bonding in ionic compounds explains these properties.
• Ionic compounds are aggregates of oppositely charged ions. These oppositely charged ions are held
together by strong electrostatic forces of attraction. A considerable amount of energy is required to
break this strong inter-ionic attraction leading to high melting and boiling points.
• Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid
is not possible due to their rigid structure. But they conduct electricity in the molten state or in
solution as ions move freely under these conditions.
✓ Carbon compounds on the other hand have low melting and boiling points as compared to ionic
compounds. From this, it can be concluded that the forces of attraction between the molecules are not
very strong. Since these compounds are largely non-conductors of electricity, we can conclude that
the bonding in these compounds does not give rise to any ions.
✓ We know that the reactivity of elements is explained as their tendency to attain a completely filled
outer shell, that is, attain noble gas configuration. Elements forming ionic compounds achieve this by
either gaining or losing electrons from the outermost shell.
✓ In the case of carbon, it has four electrons in its outermost shell (L shell) and needs to gain or lose
four electrons to attain noble gas configuration. But both these possibilities are not favourable and
hence difficult to occur. Carbon (Z =6), Electronic configuration: 2, 4
If it were to gain or lose electrons –
(i) It could gain four electrons forming C4 –
anion. But it would be difficult for the nucleus with six
protons to hold on to ten electrons, that is, four extra electrons.
(ii) It could lose four electrons forming C4+ cation. But it would require a large amount of energy
to remove four electrons leaving behind a carbon cation with six protons in its nucleus
holding on to just two electrons.

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✓ Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with
atoms of other elements. Not just carbon, but many other elements form molecules by sharing
electrons in this manner. Such bonds which are formed by the sharing of valence electrons between
two atoms are known as covalent bonds. The shared electrons ‘belong’ to the outermost shells of
both the atoms and lead to both atoms attaining the noble gas configuration. The compounds so
formed are called as covalent compounds. Covalently bonded molecules are seen to have strong bonds
within the molecule, but inter-molecular forces are weak. This gives rise to the low melting and
boiling points of these compounds. Since the electrons are shared between atoms and no charged
particles are formed, such covalent compounds are generally poor conductors of electricity. For
example, glucose, alcohol etc.
✓ Thus, atoms can combine either by transfer of valence electrons from one atom to another (gaining or
losing) or by sharing of valence electrons in order to have an octet in their valence shells. This is known
as octet rule.
Differences between ionic and covalent compounds:
Ionic compounds Covalent compounds
Formed by transfer of valence electrons from one
atom to another.
Formed by sharing of valence electrons between
the atoms.
High melting and boiling points Low melting and boiling points
Conduct electricity in molten state or in aqueous
solution
Generally, poor conductors of electricity
Constituent particles are ions, held together by
strong electrostatic force of attraction.
Constituent particles are molecules, held together
by weak intermolecular forces of attraction.
ELECTRON DOT STRUCTURES OF SOME COVALENT COMPOUNDS:
We can depict the formation of covalent compounds using electron dot structures. In this notation, dots or
crosses represent the valence electrons and the circle around the element symbol represents the
outermost/ valence shell. In a covalently bonded molecule, 8 electrons (octet) must be there within the
circle (except hydrogen, which must have the duplet i.e., 2 electrons) and the shared electrons must
belong to the outermost shells of both the bonded atoms.
The number of electrons shared by an atom during covalent bod formation is equal to number of
electron/s required to complete its octet. i.e., eight minus number of valence electrons (except H)
• The simplest molecule formed in this manner is that of hydrogen. The atomic number of hydrogen is 1.
Hence hydrogen has one electron in its K shell and it requires one more electron to fill the K shell. So
two hydrogen atoms share their electrons to form a molecule of hydrogen, H2. This allows each
hydrogen atom to attain the electronic configuration of the nearest noble gas, helium, which has two
electrons in its K shell. The shared pair of electrons is said to constitute a single covalent bond
between the two hydrogen atoms. A single covalent bond is also represented by a line between the
two atoms.
H x H
x
Hydrogen atoms
H H
x
x
Hydrogen molecule
The shared pair of electrons
(the bond pair)
Single bond between
two hydrogen atoms
H H
• Even in the case of chlorine, we see the formation of a single bond between two chlorine atoms. This is
because an atom of chlorine has seven electrons in its valence shell (the atomic number of Cl is 17) and
it requires one more electron to complete its octet. So each atom of chlorine shares one electron with

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another atom of chlorine to form a molecule of chlorine, Cl2. The one electron contributed by each
chlorine atom gives rise to a shared pair of electrons. This is said to constitute a single bond between
the two atoms. The valence electron pairs which do not take part in bonding are called non-bonding
pairs or lone pairs. In Cl2 molecule, each Cl atom has 3 lone pairs.
Atomic number of Cl: Z = 17.
Electronic configuration: 2, 8, 7
Valency = 8 – 7 = 1
Cl x
Chlorine atoms
x
x
Chlorine molecule
(the bond pair)
Single bond between
two chlorine atoms
Cl Cl
x x
x x
x
x
Cl
x
x x
x x
x
x
Cl Cl
x
x
x
x
x x x x
x x x x Non-bonding electrons
(the lone pairs)
. . . .
. . . .
.
.
.
.
• F2 molecule:
Atomic number of F: Z = 9.
Electronic configuration: 2, 7
Valency = 8 – 7 = 1
Each atom of fluorine shares one electron with another atom of fluorine giving rise to a shared pair of
electrons. This is said to constitute a single bond between the two atoms.
F x
Fluorine atoms
x
x
Fluorine molecule
(the bond pair)
Single bond between
two Fluorine atoms
x x
x x
x
x
F
x
x x
x x
x
x
F F
x
x
x
x
x x x x
x x x x Non-bonding electrons
(the lone pairs)
. . . .
. . . .
.
.
.
.
F F
• O2 molecule:
Atomic number of O: Z = 8
Valency = 8 – 6 = 2
Each atom of oxygen shares two electrons with another atom of oxygen giving rise to two shared pairs
of electrons. This is said to constitute a double bond between the two atoms.
O
Oxygen atoms Oxygen molecule
Double bond between
two Oxygen atoms
x
x
O
x
x
O O
x x
x x
x x O O
x x
x x
x x
x x
x x
x x
x x
. .
. . . .
. .
• N2 molecule:
Atomic number of N: Z = 7
Valency = 8 – 5 = 3
Each atom of nitrogen shares three electrons with another atom of nitrogen giving rise to three shared
pairs of electrons. This is said to constitute a triple bond between the two atoms.
N x
Nitrogen atoms Nitrogen molecule
Triple bond between
two Nitrogen atoms
x
x
x
x
N
x
x
x
x
x
N N
x
x
x
x
x x
x x
x x
.
.
.
.
N N

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• H2O (water) molecule:
Atomic number of O: Z = 8 Atomic number of H: Z = 1
Electronic configuration: 2, 6 Electronic configuration: 1
Valency = 8 – 6 = 2 Valency = 2 – 1 = 1
In order to achieve noble gas configuration, oxygen atom shares two electrons with two atoms of
hydrogen, i.e. one electron with each of the hydrogen atoms. Similarly, each hydrogen atom shares its
valence electron with the oxygen atom to attain duplet. This gives rise to H2O molecule containing two
oxygen-hydrogen single bonds.
H
H2
O (Water) molecule
O
H O H O H
. x x
x x
x x
x x . .
. .
H
. .
x x
H atom O atom
x x
• H2S (Hydrogen sulphide) molecule:
Atomic number of S: Z = 16 Atomic number of H: Z = 1
Electronic configuration: 2, 8, 6 Electronic configuration: 1
Valency = 8 – 6 = 2 Valency = 2 – 1 = 1
In order to achieve noble gas configuration, sulphur atom shares two electrons with two atoms of
valence electron with the sulphur atom to attain duplet. This gives rise to H2S molecule containing two
sulphur-hydrogen single bonds.
H
H2
S molecule
S
H S H S H
. x x
x x
x x
x x . .
. .
H
. .
x x
H atom S atom
x x
• NH3 (ammonia) molecule:
Atomic number of N: Z = 7 Atomic number of H: Z = 1
Valency = 8 – 5 = 3 Valency = 2 – 1 = 1
In order to achieve noble gas configuration, nitrogen atom shares three electrons with three atoms of
valence electron with the nitrogen atom to attain duplet. This gives rise to NH3 molecule containing
three nitrogen-hydrogen single bonds.
H
NH3 molecule
N
H N H N H
H
. x x
x
x x
x
. .
H
. .
x x
H atom N atom
x x
.
H
• CH4 (methane) molecule:
Atomic number of C: Z = 6 Atomic number of H: Z = 1
Valency = 8 – 4 = 4 Valency = 2 – 1 = 1

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In order to achieve noble gas configuration, carbon atom shares four valence electrons with four atoms
of hydrogen, i.e. one electron with each of the hydrogen atoms. Similarly, each hydrogen atom shares
its valence electron with the carbon atom to attain duplet. This gives rise to CH4 molecule containing
four carbon-hydrogen single bonds.
Methane is widely used as a fuel and is a major component of bio-gas and Compressed Natural Gas
(CNG). It is also one of the simplest compounds formed by carbon.
H C
.
x
x
H atom C atom
x x H C H
H
H
CH4 molecule
• CO2 (carbon dioxide) molecule:
Atomic number of C: Z = 6 Atomic number of O: Z = 8
Electronic configuration: 2, 4 Electronic configuration: 2, 6
Valency = 8 – 4 = 4 Valency = 8 – 6 = 2
In order to achieve noble gas configuration, carbon atom shares four valence electrons with two atoms
of oxygen, i.e. two electrons with each of the oxygen atoms. Similarly, each oxygen atom shares two
valence electrons with the carbon atom to attain octet. This gives rise to CO2 molecule containing two
carbon-oxygen double bonds.
C
CO2 molecule
O
O C O C O
.
x x
x x . .
. .
O
. .
x x
C atom O atom
x x
.
.
. x x
x
x
x x
x x
x . x
.
. .
. .
• S8 molecule: (Hint – The eight atoms of sulphur are joined together in the form of a ring.)
Atomic number of S: Z = 16
Electronic configuration: 2, 8, 6
Valency = 8 – 6 = 2
In order to achieve noble gas configuration, each sulphur atom shares two valence electrons with two
adjacent atoms of sulphur, i.e. one electron with each of the sulphur atoms.
S
.
S atom
.
.
.
.
.

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Allotropes of carbon:
✓ Allotropes are different forms of the same element with widely varying physical properties and the
property is called allotropy.
✓ Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the
carbon atoms are bonded to one another. The different structures result in diamond and graphite
having very different physical properties even though their chemical properties are the same.
✓ In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional
structure. The three-dimensional network involving strong C—C bonds are very difficult to break and
therefore, diamond is the hardest substance known on the earth and also has very high melting point.
It is an electrical insulator.
Diamond is a precious stone and used in jewellery. It is also used as an abrasive for sharpening hard
tools. Diamonds can be synthesised by subjecting pure carbon to very high pressure and temperature.
These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.
✓ In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a
hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Thus,
graphite has layered structure formed by the hexagonal arrays being placed in layers one above the
other. Graphite cleaves easily between the layers and, therefore, it is very soft and slippery. For this
reason graphite is used as a dry lubricant in machines running at high temperature, where oil cannot be
used as a lubricant. Being a very good conductor of electricity, graphite is used for electrodes in
batteries and industrial electrolysis. It is also used in making pencils.
✓ Fullerenes form another class of carbon allotropes, which are cage like molecules. The first one to be
identified was C-60 which has carbon atoms arranged in the shape of a football. This ball shaped
molecule has 60 vertices and each one is occupied by one carbon atom and contains 20 six- membered
rings and 12 five-membered rings. Since this looked like the geodesic dome designed by the US
architect Buckminster Fuller, the molecule was named fullerene.
Differences between diamond and graphite:
DIAMOND GRAPHITE
It has three dimensional rigid structure It has layered structure
Each carbon atom is bonded to four other
carbon atoms
Each carbon atom is bonded to three other
carbon atoms
It is the hardest substance known It is very soft and slippery
Electrical insulator Electrical conductor
VERSATILE NATURE OF CARBON:
Many things that we use contain carbon. In fact, we ourselves are made up of carbon compounds. The
numbers of carbon compounds whose formulae are known to chemists was recently estimated to be in
millions! This outnumbers by a large margin the compounds formed by all the other elements put
together. This property is seen only in carbon and no other element. The nature of the covalent bond
enables carbon to form a large number of compounds. Two factors noticed in the case of carbon are –

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(i) CATENATION: Carbon has the unique ability to form bonds with other atoms of carbon, giving rise
to large molecules. This property is called catenation. These compounds may have long chains of
carbon, branched chains of carbon or even carbon atoms arranged in rings. In addition, carbon
atoms may be linked by single, double or triple bonds. No other element exhibits the property of
catenation to the extent seen in carbon compounds. The carbon-carbon bond is very strong and
hence stable. This gives us the large number of compounds with many carbon atoms linked to each
other. Silicon forms compounds with hydrogen which have chains of up to seven or eight atoms,
but these compounds are very reactive.
(ii) TETRAVALENCY: Since carbon has a valency of four, it is capable of bonding with four other atoms
of carbon or atoms of some other elements such as oxygen, hydrogen, nitrogen, sulphur,
chlorine, etc. This gives rise to compounds with specific properties which depend on the elements
other than carbon present in the molecule. Again the bonds that carbon forms with most other
elements are very strong making these compounds exceptionally stable. One reason for the
formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the
shared pairs of electrons strongly. The bonds formed by elements having bigger atoms are much
weaker.
Organic compounds:
• The branch of chemistry which deals with the study of carbon compounds is called organic chemistry.
• Carbon compounds or organic compounds were initially extracted from natural substances and it was
thought that these compounds could only be formed within a living system. That is, it was postulated
that a ‘vital force’ was necessary for their synthesis. Friedrich Wöhler disproved this in 1828 by
preparing urea from ammonium cyanate.
• The carbon compounds, except for carbides, oxides of carbon, carbonate and hydrogen carbonate salts
continue to be studied under organic chemistry.
• The carbon compounds which contain only carbon and hydrogen are called hydrocarbons.
HYDROCARBONS
Saturated hydrocarbons
(Alkanes)
Unsaturated hydrocarbons
Alkenes Alkynes
• Hydrocarbons, which are linked by only single bonds between the carbon atoms are called saturated
hydrocarbons. These are also called as alkanes.
• Hydrocarbons having double or triple bonds between their carbon atoms are called unsaturated
hydrocarbons. The unsaturated hydrocarbons which contain one or more double bonds are called
alkenes. Those containing one or more triple bonds are called alkynes.
SATURATED AND UNSATURATED HYDROCARBONS:
In order to arrive at the structure of simple carbon compounds,
✓ The first step is to link the carbon atoms together with a single bond to get the skeletal structure.
✓ In the next step, double or triple bond is placed between the carbon atoms (applicable only in case of
alkenes or alkynes).
✓ Then use the hydrogen atoms to satisfy the remaining valencies of carbon to get the final structure.
For example, the structure of ethane is arrived in the following steps –
Step 1: Carbon atoms linked together with a single bond to get the skeletal structure.
C C

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Step 2: Three valencies of each carbon atom remain unsatisfied, so each is bonded to three hydrogen
atoms. Thus, there are 7 single bonds in ethane, i.e. one C-C and six C-H single bonds.
C C
H H
H
H
H
H
Electron dot structure of ethane.
Note: To draw the electron dot structure, each line is replaced by an electron pair. The valence electrons of
two different atoms are differentiated by dots and crosses. The circles (valence shells) are drawn in such a
way that all the atoms satisfy octet, except hydrogen (which satisfies duplet).
Similarly, the structure of ethene and ethyne are arrived in the following steps –
C C C C C C
H
H H
H
Step 1: Step 2: Step 3:
Electron dot structure of ethane (C2H4)
C C C C C C H
H
Step 1: Step 2: Step 3:
H C C
.x x
x x
.
x x
x x
H
Electron dot structure of ethyne (C2H2)
CHAINS, BRANCHES AND RINGS:
Straight chain, branched chain and cyclic carbon compounds, all may be saturated or unsaturated.
1) ALKANES:
• Alkanes are saturated hydrocarbons with the general formula, CnH2n+2; n = 1,2,3,4. . . . etc.
• Formulae and structures of the first six members of alkanes are given in Table below:

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• Up to propane (C3H8), only one carbon skeleton is possible. From, butane onwards more than one
carbon skeletons are possible giving rise to structural isomers.
• Two or more compounds with identical molecular formula but different structures are called
structural isomers. To write the possible skeletal structures, the length of the straight chain of carbon
atoms is successively reduced by one carbon atom and that carbon atom is attached as a branch to any
of the non-terminal carbon atoms.
Note: In case of equivalent non-terminal carbon atoms, any one to be considered for the attachment.
✓ Let us take another look at butane. If we make the carbon ‘skeleton’ with four carbon atoms, we see
that two different possible ‘skeletons’ are –
C C C
C C C
C
C
Filling the remaining valencies with hydrogen gives us –
C C C
C H
H
H
H
H
H
H
H
H
H C C
C
C
H
H
H
H
H
H
H
H
H
H
n-Butane
(Linear isomer)
Isobutane
(Branched isomer)
We see that both these structures have the same formula C4H10. Thus, butane has 2 structural
isomers.
✓ There are three structural isomers for pentane (C5H12) as follows: [one linear and two branched chain
hydrocarbons]
C C
C
C
C
C C C
C C C C
C
C
C
C C C
C C
H
H
H
H
H
H
H
H
H H
H
H
C C
C
C
H
H
H
H
H
H
H
H
H
C H
H
H
n-Pentane
(Linear isomer)
Isopentane
(Branched isomer)
C C
C
C
H
H
H
H
H
H
H
H
C
H
H
H
H
Neopentane
(Branched isomer)
✓ Similarly, alkane corresponding to the molecular formula C6H14 (Hexane) has five structural isomers.
C C
C
C
C C
C C C
C C C
C C
C
C
C
C
C C
C C C
C
C C
C
C
C
C
C C C
C C
H
H
H
H
H
H
H
H
H C
H
H
H
H
H
C C
C
C
H
H
H
H
H
H
H
H
H
C C
H
H
H
H
H
C C
C
C
H
H
H
H
H
H
H
C
H
H
H
H
C H
H
H
C C
C
C
C
H
H
H
H
H
H
H
H
C
H
H
H
H
H
H
C C
C
C
H
H
H
H
H
H
H
H
C H
H
H
C
H
H
H

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• In addition to straight and branched carbon chains, some compounds have carbon atoms arranged in
the form of a ring. Saturated compounds in which carbon atoms are arranged in the form of a ring are
called cycloalkanes. Their names are derived by prefixing ‘cyclo‘ to the name of the corresponding
straight chain alkane. These follow the general formula, CnH2n; n = 3, 4, 5 . . . etc.
No. of C atoms Name Formula Structure
3 Cyclopropane C3H6
C
C
C
H
H
H
H
H H
4 Cyclobutane C4H8
C C
C
C
H
H H
H
H H
H
H
5 Cyclopentane C5H10
C
C C
C C
H
H
H
H
H
H
H
H
H
H
6 Cyclohexane C6H12
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
H
H
C
C C
C
C
x
x
x x
x
x
x x
x
x
H H
H
H
H
H
H
H
H
H
x
x x
x
x
x
x
x
x
x
.
.
.
.
.
.
.
.
. .
C
C C
C
C
x
x
x x
x
x
H H
H
H
H
x
x x
x
x
.
.
.
. .
C
x
x
x x
x
x
x
x
x
x
x
x
x
.
.
. .
..
.
H
H
H H
H
H
H
Electron dot strucutre of cyclopentane
Electron dot strucutre of cyclohexane
2) ALKENES:
• Alkenes are unsaturated hydrocarbons with the general formula, CnH2n; n = 2, 3, 4. . . . etc.
• Formulae and structures of the first three members of alkenes are given in Table below:
No. of C atoms Name Formula Structure No. of shared electrons
2 Ethene C2H4
C C
H
H H
H 6 x 2 = 12
3 Propene C3H6
C
C
H
H
C H
H
H
H
9 x 2 = 18
4 Butene C4H8
C
C
H
H
C C
H
H
H
H
H
H
12 x 2 = 24
• Since cycloalkanes also follow the same general formula, CnH2n, we can also write carbon skeleton
involving cyclic ring structure. Thus propene (C3H6), onwards more than one carbon skeletons are
possible giving rise to structural isomers. For example,
Hydrocarbon with the formula C3H6 has 2 structural isomers.

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C C C C
C
C
Or
C C
C
C C C
H
H
H
H
H
H
C
C
C H
H
H
H
H
H
Or
C C
C
H
H
H
H
H
H
Propene (linear chain isomer) Cyclopropane (cyclic chain isomer)
(unsaturated hydrocarbon) (saturated hydrocarbon)
Similarly, hydrocarbon with the formula C4H8 has 4 structural isomers, in total. i.e. 2 linear chain, 1
branched chain and 1 cyclic chain isomer. It may be noted that cyclic isomer is saturated whereas other
isomers are unsaturated.
C C C
C H
H
H
H
H
H
H
H C C
C
C
H
H
H H
H
H
H
H
1- Butene / But-1-ene
(Linear isomer)
Isobutene
(Branched isomer)
C C C
C H
H
H
H
H
H
H
H
C C C
C
C C C
C C C
C
C
2- Butene / But-2-ene
(Linear isomer)
or
C C C
C
or or
C C
C
C
C C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
C C
C C
Cyclobutane
(cyclic chain isomer)
In addition to straight and branched carbon chains, some unsaturated compounds have carbon atoms
arranged in the form of a ring. For example, benzene, C6H6, has the following structure –
C
C
C
C
C
C
H
H
H
H
H
H
Benzene has 3 C-C single bonds, 3 C-C double bonds and 6 C-H single bonds.
3) ALKYNES:
• Alkynes are unsaturated hydrocarbons with the general formula, CnH2n – 2; n = 2, 3, 4. . . . etc.
• Formulae and structures of the first three members of alkynes are given in Table below:
No. of C atoms Name Formula Structure No. of shared electrons
2 Ethyne C2H2 C C
H H 5 x 2 = 10
3 Propyne C3H4
C
C C H
H
H
H
8 x 2 = 16
4 Butyne C4H6
C
C C C
H
H
H
H
H
H
11 x 2 = 22
From, butyne (C4H6) onwards structural isomers are possible. For example, C4H6 has 2 isomers.
C
C C H
H
H
C
H
H
H
C
C C C
H
H
H
H
H
H
1 -Butyne / But-1-yne 2 - Butyne / But-2-yne
C
C C C C
C C
C
C
C C C
or

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FUNCTIONAL GROUPS:
• In addition to carbon and hydrogen, carbon atom also forms bonds with other elements such as
halogens, oxygen, nitrogen and sulphur. In a hydrocarbon chain, one or more hydrogens can be
replaced by these elements, such that the valency of carbon remains satisfied. In such compounds, the
element replacing hydrogen is referred to as a heteroatom. Thus, atoms other than carbon and
hydrogen are heteroatoms.
• Heteroatoms or the group containing heteroatoms confer specific chemical properties to the
compound, regardless of the length and nature of the carbon chain and hence are called functional
groups. Thus, organic compounds with the same functional group exhibit very similar chemical
properties and those with different functional groups show different chemical properties.
For example, the chemical properties of CH3OH, C2H5OH, C3H7OH and C4H9OH are all very similar as
they possess the same functional group, alcohol which decides the chemical properties of these
compounds, regardless of the length of the carbon chain. On the other hand, the chemical properties
CH3Br, CH3OH, CH3COOH and CH3CHO are very different as they possess different functional groups.
• Some important functional groups are given in the table below. Free valency or valencies of the group
are shown by the single line. The functional group is attached to the carbon chain through this valency
by replacing one hydrogen atom or atoms.
• Aldehyde and carboxylic acid groups always occur at the terminal position of the carbon chain whereas
ketonic group always occurs at the non-terminal position.
HOMOLOGOUS SERIES:
✓ A series of organic compounds containing the same functional group (if any) in which successive
members differ from each other by a –CH2– unit forms a homologous series and the members of the
series are called homologues. The homologues can be represented by general molecular formula.
✓ The successive members differ from each other in molecular formula by a –CH2– unit. In terms of
molecular mass, the successive members differ from each other by 14u. i.e., (1 × 12u) + (2 × 1u) = 14u
✓ There are a number of homologous series of organic compounds. Some of these are alkanes, alkenes,
alkynes, haloalkanes, alcohols, aldehydes, ketones, carboxylic acids etc.
Alkanes: CH4, C2H6, C3H8, C4H10……… In general, CnH2n+2; n = 1, 2, 3…
Alkenes: C2H4, C3H6, C4H8, C5H10 ……… In general, CnH2n; n = 2, 3, 4…
Alkynes: C2H2, C3H4, C4H6, C5H8 ……… In general,CnH2n–2; n = 2, 3, 4…
Note: In alkenes and alkynes, the first member has 2 carbon atoms.
Haloalkanes: CH3X, C2H5X, C3H7X, C4H9X……… In general, CnH2n+1X; n = 1, 2, 3… (X = F, Cl, Br or I)
Alcohols: CH3OH, C2H5OH, C3H7OH, C4H9OH……… In general, CnH2n+1OH; n = 1, 2, 3…

13 | P a g e
Aldehydes: HCHO, CH3CHO, C2H5CHO, C3H7CHO………
In general, CnH2n+1CHO; n = 0, 1, 2, 3… or CnH2nO; n = 1, 2, 3…
Ketones: CH3COCH3, CH3CH2COCH3, CH3CH2CH2COCH3………
In general,CnH2nO; n = 3, 4, 5…
Note: In ketones, the first member has 3 carbon atoms.
It is important to note that aldehydes and ketones can be represented by the same general formula,
CnH2nO. This suggests that the two compounds can exist as structural isomers. For example, C3H6O has
two structural isomers.
C C C
O
H
H
H
H
H
H
Propanone
( Ketone)
C C C
H
H
H
H
H
O
H
Propanal
(Aldehyde)
The two compounds have same molecular formula, but different structures. Structural isomers with
different functional groups are called functional isomers.
Carboxylic acids: HCOOH, CH3COOH, C2H5COOH, C3H7COOH… In general,CnH2n+1COOH; n = 0, 1, 2, 3…
✓ As the molecular mass and molecular size increases in any homologous series, a gradation in physical
properties is seen.
• The melting and boiling points increase in any homologous series with increasing molecular mass and
molecular size. This is due to increase in the strength of intermolecular forces (van der waal forces) of
attraction. For example, the boiling points of alcohols increase in the order,
CH3OH < C2H5OH < C3H7OH < C4H9OH….so on
• Other physical properties such as solubility in a particular solvent also show a similar gradation. For
example, alcohols being polar are soluble in polar solvent like water. But their solubility in water
decreases with increase in the length of carbon chain (molecular size). This is due increase in non-polar
character or hydrophobic (water repelling) nature. The solubility of alcohols in water decreases in the
order,
CH3OH > C2H5OH > C3H7OH > C4H9OH….so on
✓ But the chemical properties, which are determined solely by the functional group, remain similar in a
homologous series. This is because, all the members of a homologous series possess the same
functional group. Thus, the chemical properties of CH3OH, C2H5OH, C3H7OH and C4H9OH are all very
similar.
NOMENCLATURE OF CARBON COMPOUNDS:
There are two systems of nomenclature.
(i) Trivial or common nomenclature (ii) IUPAC nomenclature.
(i) Trivial or common nomenclature:
▪ These names are conventional or traditional and were assigned based on their source or origin.
For instance, citric acid is named so because it is found in citrus fruits. The acid found in red ant is named
formic acid (Latin word; ant = formica) and acetic acid is derived from vinegar (Latin word; acetum =
vinegar).
(ii) IUPAC nomenclature:
▪ In order to clearly identify, a systematic method of naming has been developed and is known as the
IUPAC (International Union of Pure and Applied Chemistry) system of nomenclature. In this
systematic nomenclature, the names are correlated with the structure such that the reader or listener
can deduce the structure from the name or vice versa.

14 | P a g e
The IUPAC System of Nomenclature:
✓ The IUPAC name of an organic compound consists of three parts, namely,
a) Root word b) Suffix(es) c) Prefix(es)
✓ The complete systematic IUPAC name can be represented as:
Prefix + Root word + suffix
Root word: It indicates the number of carbon atoms in the longest possible continuous carbon chain
known as parent chain chosen by a set of rules.
Suffix: It is used to indicate the functional group in the organic compound and is added immediately
after the root word.
Prefix: The prefix is used to indicate the side chains and low priority functional groups (such as
halogens). The prefix is added immediate before the root word.
✓ Naming a carbon compound can be done by the following method –
(a) First of all, the longest carbon chain in the molecule is identified, referred to as parent carbon
chain. It is named using appropriate root word. For example, a compound having three carbon
atoms would have the name propane.
(b) If the carbon chain is unsaturated, then the final ‘ane’ in the name of the carbon chain is
substituted by ‘ene’ or ‘yne’. For example, a three-carbon chain with a double bond would be called
propene and if it has a triple bond, it would be called propyne.
(c) In case a functional group is present, it is indicated in the name of the compound with either a
prefix or a suffix. The prefix is used to represent the halogens and for other functional groups,
appropriate suffix is used. For example, a compound having two carbon atoms containing chlorine
would have the name chloroethane.
(d) If the name of the functional group is to be given as a suffix, and the suffix of the functional group
begins with a vowel a, e, i, o, u, then the name of the carbon chain is modified by deleting the final
‘e’ and adding the appropriate suffix. For example, a three-carbon chain with a ketone group would
be named in the following manner –
Propane – ‘e’ = propan + ‘one’ = propanone
CLASS OF COMPOUNDS PREFIX/SUFFIX EXAMPLE
ALKANE Suffix – ane
C C C
H
H
H
H
H
H
H
H
Propane
or CH3CH2CH3
ALKENE Suffix – ene
C C C
H
H
H
H
H
H
Propene
or CH3CH=CH2
ALKYNE Suffix – yne
C C C
H
H
H
H
Propyne
or CH3C≡CH
HALOALKANE Preffix – Chloro, Bromo,
etc C C C
H
H
H
H
Cl
H
H
H
Choropropane
or CH3CH2CH2Cl

15 | P a g e
C C C
H
H
H
H
Br
H
H
H
Bromopropane
or CH3CH2CH2Br
ALCOHOL Suffix – ol
C C C
H
H
H
H
O
H
H
H
H
Propanol
or CH3CH2CH2OH
ALDEHYDE Suffix – al
C C C
H
H
H
H
H
O
H
Propanal
or CH3CH2CHO
KETONE Suffix – one
C C C
O
H
H
H
H
H
H
Propanone
or CH3COCH3
CARBOYLIC ACID Suffix – oic acid
C C C
H
H
H
H
O
O
H
H
Propanoic acid
or CH3CH2COOH
(A) Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane (iii) Butanone (iv) Hexanal.
C C O
H
H
H
H
O
C C C
H
H
H
H
H
H
H
C C Br
H
H
H
H
C C C
O
H
H
H
H
H
C
H
H
H
(i) (ii) (iii) (iv)
C C C
H
H
H
C C C
H
H
H
H
H
O
H
H
H
H
Ethanoic acid Bromopentane Butanone Hexanal
(B) Are structural isomers possible for bromopentane?
Yes. Because more than one carbon skeletons are possible. Further, bromine can occupy different
positions in the same carbon skeleton. In total, 2𝑛−2
= 25 −2
= 8 structural isomers.
Note: The formula, 2𝑛−2
is applicable only for haloalkanes. (n = no. of carbon atoms)
(C) How would you name the following compounds?
C
H3 CH2 Br
(i) (ii) (iii)
C C C
H
H
H
C C C
H
H
H
H
H
H
H
Bromoethane
C O
H
H
Methanal
Hexyne
CHEMICAL PROPERTIES OF CARBON COMPOUNDS:
(a) Combustion:
✓ Carbon compounds can be easily oxidised on combustion. Carbon, in all its allotropic forms, burns in
oxygen to give carbon dioxide along with the release of heat and light. Most carbon compounds also
release a large amount of heat and light on burning. These are the oxidation reactions.
C + O2 → CO2 + heat and light
CH4 + 2O2 → CO2 + 2H2O + heat and light
CH3CH2OH + 3O2 → 2CO2 + 3H2O + heat and light
✓ Presence of carbon in a compound can be tested by burning it and passing the liberated gas through
lime water. Carbon compounds produce carbon dioxide on combustion, which turns lime water milky.
✓ Due to the evolution of large amount of heat during combustion, alkanes are used as fuels.

16 | P a g e
✓ Some of the commonly used fuels are a mixture of hydrocarbons and are sources of energy. e.g.,
▪ LPG (Liquified petroleum gas): Butane is the major constituent.
▪ CNG (Compressed natural gas)/LNG (Liquified natural gas): Methane is the major constituent.
▪ Petrol (octane is the major constituent), diesel and kerosene oil.
▪ Coal gas, etc.
✓ Saturated hydrocarbons will generally give a clean blue flame while unsaturated carbon compounds
will give a yellow flame with lots of black smoke. Unsaturated hydrocarbons undergo incomplete
combustion due to the higher percentage of carbon content giving luminous yellow flame with lots of
black smoke. This results in a sooty deposit on the metal plate placed above the yellow flame. A
luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. The
soot formed due to incomplete combustion is carbon, which at higher temperature starts to glow with
yellow light, i.e. it emits yellow radiations.
✓ However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons
giving a sooty flame. The gas/kerosene stove used at home has inlets for air so that a sufficiently
oxygen-rich mixture is burnt to give a clean blue flame. If you observe the bottoms of cooking vessels
getting blackened, it means that the air holes are blocked and fuel is getting wasted due to incomplete
combustion.
✓ Even unsaturated hydrocarbons undergo complete combustion and burn with high temperature blue
flame when burnt in sufficient oxygen. For example, when ethyne/acetylene is burnt in air, it gives a
sooty flame due to incomplete combustion. But when burnt in sufficient oxygen, it burns with a clean
blue flame with a high temperature due to complete combustion. Ethyne/acetylene is used for arc
welding purposes in the form of oxyacetylene flame obtained by mixing acetylene with oxygen gas.
Non-luminous flame Luminous flame
It is a clean blue non-sooty flame It is a yellow sooty flame
Formed due to complete combustion of fuels Formed due to incomplete combustion of fuels
Relatively higher temperature flame. Relatively lower temperature flame.
Saturated hydrocarbons will generally give a
clean blue flame
Unsaturated hydrocarbons will generally give a
yellow flame
✓ Coal or charcoal in an ‘angithi’ sometimes just glows red and gives out heat without a flame. This is
because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited,
the volatile substances present vapourise and burn with a flame in the beginning.
✓ Coal and petroleum have been formed from biomass, i.e. from dead remains of plants and animals
which has been subjected to various biological and geological processes. Hence they are called fossil
fuels. Coal is the remains of trees, ferns, and other plants that lived millions of years ago. These were
crushed into the earth, perhaps by earthquakes or volcanic eruptions. They were pressed down by
layers of earth and rock. They slowly decayed into coal. Oil and gas are the remains of millions of tiny
plants and animals that lived in the sea. When they died, their bodies sank to the sea bed and were
covered by silt. Bacteria attacked the dead remains, turning them into oil and gas under the high
pressures they were being subjected to. Meanwhile, the silt was slowly compressed into rock. The oil
and gas seeped into the porous parts of the rock, and got trapped like water in a sponge.
(b)Oxidation:
✓ Carbon compounds can be easily oxidised on combustion. In addition to this complete oxidation, we
have reactions in which alcohols are converted to carboxylic acids.
Substances capable of adding oxygen to others are known as oxidising agents. Alkaline potassium
permanganate (KMnO4) or acidified potassium dichromate (K2Cr2O7) oxidise alcohols to acids, that is,
add oxygen to the starting material. Hence they are known as oxidising agents.
CH3
-CH2
OH
Alkaline KMnO4
+ Heat
or Acidified KMnO4
+ Heat
CH3
-COOH
Ethanol
(Ethyl alcohol)
Ethanoic acid
(Acetic acid)

17 | P a g e
✓ Alkaline potassium permanganate (KMnO4) is dark purple coloured solution. When a solution of
alkaline potassium permanganate is added drop by drop to warm ethanol, its purple colour disappears.
It is because, it oxidises ethanol to ethanoic acid and itself gets reduced to a colourless compound. But
the colour does not disappear when excess of potassium permanganate is added. This is because, after
the completion of oxidation reaction, the excess KMnO4 remains unreacted.
(c) Addition reaction:
✓ Addition reactions are characteristic reactions of unsaturated hydrocarbons. Saturated hydrocarbons
do not undergo addition reactions.
✓ It involves the addition of simple molecules such as H2, Cl2, H2O etc. to the double bond or triple bond
to give saturated compounds.
✓ Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to
give saturated hydrocarbons. This reaction is called catalytic hydrogenation. Catalysts are substances
that cause a reaction to occur or proceed at a faster rate without the reaction itself being affected.
C C
H
H H
H
H2
Palladium catalyst
C C H
H
H
H
H
H
+
Ethene Ethane
C C
H H 2 H2
Palladium catalyst
C C H
H
H
H
H
H
+
Ethyne
Ethane
This
reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils
generally have long unsaturated carbon chains which on hydrogenation get reduced saturated carbon
chains.
Vegetable oils (l) + H2 (g)
𝑁𝑖𝑐𝑘𝑒𝑙 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡
→ Vegetable ghee (s)
C C
R
R R
R
H2
Nickel catalyst
C C R
R
H
R
R
H
✓ Animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils
containing unsaturated fatty acids are ‘healthy’ and should be chosen for cooking.
✓ Addition of bromine to unsaturated hydrocarbon results in the discharge of reddish orange colour of
bromine to give saturated compound. Since only unsaturated hydrocarbons undergo this reaction, it
can be used as a test for unsaturation.
C C
H
H H
H
Br2
(aq)
C C H
H
Br
H
H
Br
(d)Substitution reaction:
✓ It involves the replacement of one type of atom or group of atoms by another type of atom or group.
✓ Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents. However,
in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can
replace the hydrogen atoms one by one. It is called a substitution reaction because one type of atom or
a group of atoms takes the place of another. A number of products are usually formed with the higher
homologues of alkanes.
CH4 + Cl2
𝑆𝑢𝑛 𝑙𝑖𝑔ℎ𝑡
→ CH3Cl + HCl
Methane Chloromethane
CH3Cl + Cl2
→ CH2Cl2 + HCl
Chloromethane Dichloromethane
CH2Cl2 + Cl2
→ CHCl3 + HCl
Dichloromethane Trichloromethane (Chloroform)

18 | P a g e
CHCl3 + Cl2
→ CCl4 + HCl
Trichloromethane Tetrachloromethane
These reactions involve the successive replacement of hydrogen atoms by chlorine to give CCl4.
SOME IMPORTANT CARBON COMPOUNDS – ETHANOL AND ETHANOIC ACID
ETHANOL (C2H5OH or CH3CH2OH):
C C O
C C
H
H
H
O H
H
H
..
..
H
H
H H
H
H
X
X
X
.
X
.
X . X .
X . X .
. .
. .
.
.
Properties of Ethanol:
✓ Ethanol is a liquid at room temperature. The melting and boiling points of ethanol are 156K and 351K
respectively.
✓ Ethanol is commonly called alcohol and is the active ingredient of all alcoholic drinks. In addition,
because it is a good solvent, it is also used in medicines such as tincture iodine, cough syrups, and many
tonics. Ethanol is also soluble in water in all proportions.
✓ Consumption of small quantities of dilute ethanol causes drunkenness. Even though this practice is
condemned, it is a socially widespread practice. However, intake of even a small quantity of pure
ethanol (called absolute alcohol) can be lethal. Also, long-term consumption of alcohol leads to many
health problems.
✓ When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress
the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering
of the normal inhibitions, and finally stupor. The individual may feel relaxed without realising that his
sense of judgement, sense of timing, and muscular coordination have been seriously impaired.
✓ Unlike ethanol, intake of methanol in very small quantities can cause death. Methanol is oxidised to
methanal in the liver. Methanal reacts rapidly with the components of cells. It coagulates the
protoplasm, in much the same way an egg is coagulated by cooking. Methanol also affects the optic
nerve, causing blindness.
Reactions of Ethanol:
(i) Reaction with sodium:
• Sodium being a highly reactive metal displaces hydrogen from its compounds such as acids, water,
alcohols etc.
• Alcohols react with sodium leading to the evolution of hydrogen gas to give sodium alkoxides. For
example, ethanol reacts with sodium to give sodium ethoxide liberating H2 gas. The liberated H2 gas
can be tested by burning. Hydrogen gas burns with a pop sound.
2 Na + 2 CH3CH2OH 2 CH3CH2O-
Na+
+ H2
(Sodium ethoxide)
(ii) Reaction to give unsaturated hydrocarbon:
• Heating ethanol at 443 K with excess concentrated sulphuric acid results in the dehydration (removal of
water) of ethanol to give ethene. Dehydration of alcohols is an example for elimination reaction.
C C
H OH
H
H H
H
Conc. H2
SO4
443K
C C
H
H H
H
or CH3
CH2
OH
Hot conc. H2
SO4
CH2
=CH2
+ H2
O
+ O
H2
Ethanol Ethene
• The concentrated sulphuric acid can be regarded as a strong dehydrating agent which removes water
from ethanol.

19 | P a g e
Uses of ethanol:
a) Ethanol is an important industrial solvent. To prevent the misuse of ethanol produced for industrial
use, it is made unfit for drinking by adding poisonous substances like methanol to it. Dyes are also
added to colour the alcohol blue so that it can be identified easily. This is called denatured alcohol.
b) Sugarcane plants are one of the most efficient convertors of sunlight into chemical energy. Sugarcane
juice can be used to prepare molasses which is fermented to give alcohol (ethanol). Some countries
now use alcohol as an additive in petrol since it is a cleaner fuel which gives rise to only carbon dioxide
and water on burning in sufficient air (oxygen).
Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their
combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the
environment.
ETHANOIC ACID (CH3COOH):
C C O
C C
H
H
H
O H
O
..
..
H
H
H
H
X
X
X
.
X
.
X .
X .
. .
. .
.
.
..
..
X .
X .
O
..
..
Properties of ethanoic acid:
✓ Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids.
✓ The group of organic compounds called carboxylic acids are characterised by their acidic nature.
However, they are weaker acids than mineral/inorganic acids. Unlike mineral acids like HCl, which are
completely ionised, carboxylic acids are partially ionised in water. Since dilute acetic acid and dilute
hydrochloric acid differ in H+
ion concentration, they give different colour with pH paper/ universal
indicator.
✓ 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles. The
melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates.
This gave rise to its name glacial acetic acid.
Reactions of ethanoic acid:
(a) Reaction with a base: Like mineral acids, ethanoic acid reacts with a base such as sodium hydroxide to
give a salt (sodium ethanoate or commonly called sodium acetate) and water. However, the reaction is
less exothermic compared to that of mineral acids.
NaOH + CH3COOH → CH3COONa + H2O
Note: In case of salts derived from organic acids, anion is generally written first followed by cation.
(b) Reaction with carbonates and hydrogen carbonates:
• Like mineral acids, ethanoic acid reacts with carbonates and hydrogen carbonates to give a salt, carbon
dioxide and water. The salt produced is commonly called sodium acetate.
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
• The reaction takes place with brisk effervescence/fizzing due to the evolution of CO2 gas. The liberated
CO2 gas can be tested by passing through freshly prepared lime-water, which turns milky.
• This reaction can be used to distinguish between an alcohol and a carboxylic acid. Alcohols do not
react with carbonates and hydrogen carbonates.

20 | P a g e
(c) Esterification reaction:
• Esters are derivatives of carboxylic acids, most commonly formed by reaction of a carboxylic acid
and an alcohol in the presence of acid catalyst. The reaction is called esterification. It is a reversible
reaction. For example, ethanoic acid reacts with absolute ethanol in the presence of an acid
catalyst like conc. H2SO4 to give an ester, ethyl ethanoate or ethyl acetate.
CH3
COOH + CH3
CH2
OH CH3
COOCH2
CH3
+ H2
O
Acid
Ethanoic acid
(Acetic acid)
Ethanol
(Ethyl alcohol)
Ethyl ethanoate
(Ethyl acetate)
C
H3 C OH
O
+ H O CH2 CH3
- - - - - - - - - - - -
- - - - - - - - - - - -
-
-
-
-
-
-
-
-
-
-
C
H3 C O
O
CH2 CH3 + O
H2
Acid
or
• The acid catalyst used acts as a dehydrating agent.
• Generally, esters are sweet-smelling substances. These are used in making perfumes and as
flavouring agents.
• Ester on treating with sodium hydroxide, which is an alkali, is converted back to alcohol and
sodium salt of carboxylic acid. This reaction is known as saponification because it is used in the
preparation of soap.
CH3
COOCH2
CH3
+ NaOH CH3
COONa + CH3
CH2
OH
Sodium salt of ethanoic acid
(Sodium ethanoate/Sodium acetate)
Ethyl ethanoate
(Ethyl acetate)
Ethanol
• Soaps are sodium or potassium salts of long chain carboxylic acids/fatty acids. Soaps containing
sodium salts are formed by heating ester of fatty acid (i.e., fat) with aqueous sodium hydroxide
solution.
SOAPS AND DETERGENTS:
✓ Soaps and detergents are used as cleansing agents. These improve cleansing properties of water and
help in removal of fats which bind other materials to the fabric or skin.
✓ Soaps used for cleaning purpose are sodium or potassium salts of long chain fatty acids, e.g. sodium
stearate, (sodium salt of stearic acid) C17H35COO–
Na+
, which is a major component of many bar soaps.
When dissolved in water, it dissociates into C17H35COO–
and Na+
ions
✓ Soaps containing sodium salts are formed by heating ester of fatty acid (i.e., fat) with aqueous sodium
hydroxide solution.
✓ The effect of soap in cleaning can be demonstrated by performing following activity.
▪ About 10 mL of water is taken in each of the two test tubes.
▪ A drop of oil (cooking oil) is added to both the test tubes and labelled as A and B.
▪ To the test tube B, a few drops of soap solution is added.

21 | P a g e
▪ Both the test tubes are shaken vigourously for the same period of time and left undisturbed for
some time.
▪ We observe that the oil layer starts to separate and this happens first in test tube A.
▪ In test tube B, the oil layer takes longer time to separate.
✓ The above observations can be explained as follows:
Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it
interacts with water, while the other end is hydrophobic, that is, it interacts with hydrocarbons. Most
dirt is oily in nature and as we know, oil does not dissolve in water. The polar ionic-end of soap
interacts with water while the non-polar carbon chain interacts with oil. The soap molecules, thus form
structures called micelles (see figure below) where one end of the molecules is towards the oil droplet
while the ionic-end faces outside. This forms an emulsion in water. Thus, it takes longer time for oil to
separate out in test tube B.
Mechanism of the cleaning action of soaps:
✓ Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it
interacts with water, while the other end is hydrophobic, that is, it interacts with hydrocarbons.
✓ When soap is at the surface of water, the hydrophobic ‘tail’ of soap will not be soluble in water and the
soap will align along the surface of water with the ionic end in water and the hydrocarbon ‘tail’
protruding out of water.
(a) Arrangement of stearate ions on the surface. (b) Arrangement of stearate ions inside the bulk (micelle)
✓ Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion out of
the water. Thus, clusters of molecules are formed in which the hydrophobic tails are in the interior of
the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.
Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the
micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of
ion-ion repulsion. Thus, the dirt suspended in the micelles is also easily rinsed away. The soap micelle
thus helps in pulling out the dirt in water and we can wash our clothes clean.
✓ People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes
on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine.

22 | P a g e
This is necessary for pulling out the oil droplet surrounded by stearate ions in water and remove it from
the dirty surface.
Soap solution behaves as a colloid. The soap micelles are large enough to scatter light. Hence a soap
solution appears cloudy. Scattering of light by colloidal particles is called Tyndall effect.
Hard and Soft Water:
• Rain water is almost pure (may contain some dissolved gases from the atmosphere). Being a good
solvent, when it flows on the surface of the earth, it dissolves many salts.
• Presence of calcium and magnesium salts in the form of hydrogen carbonate, chloride and sulphate in
water makes water ‘hard’. Hard water does not give foam/lather with soap. Hard water forms scum/
white curdy precipitate with soap. It is, therefore, unsuitable for laundry. It is harmful for boilers as
well, because of deposition of salts in the form of scale, which reduces the efficiency of the boiler. For
example, soap containing sodium stearate (C17H35COONa) reacts with hard water to precipitate out
Ca/Mg stearate.
2C17H35COONa + CaCl2 → 2NaCl + (C17H35COO)2Ca
Soap Insoluble precipitate
• Water free from soluble salts of calcium and magnesium is called Soft water. It gives foam/lather with
soap easily. It does not form scum/precipitate with soaps.
Hard water Soft water
It contains soluble salts of calcium and
magnesium in the form of hydrogen carbonate,
chloride and sulphate.
It is free from soluble salts of calcium and
magnesium
It does not give foam/lather with soap It gives foam/lather with soap easily
It forms scum/ precipitate with soap It does not form scum/precipitate with soap
• While bathing if foam is formed with difficulty and an insoluble substance (scum) remains after
washing, then it indicates that the water is ‘hard’. The scum is formed because of the reaction of soap
with the calcium and magnesium salts, which cause the hardness of water. Hence we need to use a
larger amount of soap. This problem is overcome by using another class of compounds called
detergents as cleansing agents.
• Detergents are generally sodium salts of sulphonic acids or ammonium salts with chlorides or
bromides ions, etc. Both have long hydrocarbon chain. Hence, the mechanism of micelle formation
here also is same as that of soaps. The charged ends of these compounds do not form insoluble
precipitates with the calcium and magnesium ions in hard water. Thus, detergents remain effective
even in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.
• Detergents give foam with both soft as well as hard water. On the other hand, soaps give foam easily
with soft water but form scum/precipitate with hard water. Thus, we can check if water is hard by using
a soap but not detergent.

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