Carbon and its compounds Notes | EduRev

: Carbon and its compounds Notes | EduRev

 Page 1


1
Carbonand
ItsCompounds
Carbon, a non-metal with atomic number 6 and mass number 12, occurs in
free as well as in combined form. All living creatures are based on it. Its amount in
the earth’s crust and in the atmosphere is quite meagre. In earth’s crust, there is
only 0.02% carbon which is present as minerals and in the atmosphere 0.03%
carbon is present in the form of carbon dioxide. Carbon thus forms a large
number of compounds with itself and with the atoms of other elements; some of
which are studied in this chapter.
Bonding in Carbon Compounds :
The Covalent Bond
Atomic number of carbon is 6, so there are 4 electrons in its outermost shell
and it needs to gain or loss 4 electrons in order to attain a stable configuration,
i.e., noble gas configuration.
The octet can be completed by following two ways
(i) It could lose 4 electrons and form C
4+
cation. But a massive amount of
energy is required to remove 4 electrons leaving behind a carbon cation
with 6 protons in its nucleus holding on to just two electrons.
(ii) It could gain 4 electrons and can formC
4-
anion. But for a nucleus having
6 protons, it would be difficult to hold on to 10 electrons, i.e., 4 extra
electrons.
In order to overcome this problem, carbon shares its valence electrons with its
other atoms or atoms of other elements.
These shared electrons belong to the outer shells of both the atoms and in this
way, both atoms attain the noble gas configuration. This type of bonding is called
covalent bonding. Thus, the bonds which are formed by the sharing of an electron
pair between two same or different atoms are known as covalent bonds.
ll ne
3 Bonding in Carbon
Compounds: The Covalent
Bond
3 Allotropes of Carbon
3 Versatile Nature of
Carbon
3 Organic Compounds
3 Hydrocarbons
3 Functional Groups
3 Nomenclature of Carbon
Compounds
3 Chemical Properties of
Carbon Compounds
3 Fuels and Flames
3 Some Important Carbon
Compounds
3 Soaps and Detergents
Page 2


1
Carbonand
ItsCompounds
Carbon, a non-metal with atomic number 6 and mass number 12, occurs in
free as well as in combined form. All living creatures are based on it. Its amount in
the earth’s crust and in the atmosphere is quite meagre. In earth’s crust, there is
only 0.02% carbon which is present as minerals and in the atmosphere 0.03%
carbon is present in the form of carbon dioxide. Carbon thus forms a large
number of compounds with itself and with the atoms of other elements; some of
which are studied in this chapter.
Bonding in Carbon Compounds :
The Covalent Bond
Atomic number of carbon is 6, so there are 4 electrons in its outermost shell
and it needs to gain or loss 4 electrons in order to attain a stable configuration,
i.e., noble gas configuration.
The octet can be completed by following two ways
(i) It could lose 4 electrons and form C
4+
cation. But a massive amount of
energy is required to remove 4 electrons leaving behind a carbon cation
with 6 protons in its nucleus holding on to just two electrons.
(ii) It could gain 4 electrons and can formC
4-
anion. But for a nucleus having
6 protons, it would be difficult to hold on to 10 electrons, i.e., 4 extra
electrons.
In order to overcome this problem, carbon shares its valence electrons with its
other atoms or atoms of other elements.
These shared electrons belong to the outer shells of both the atoms and in this
way, both atoms attain the noble gas configuration. This type of bonding is called
covalent bonding. Thus, the bonds which are formed by the sharing of an electron
pair between two same or different atoms are known as covalent bonds.
ll ne
3 Bonding in Carbon
Compounds: The Covalent
Bond
3 Allotropes of Carbon
3 Versatile Nature of
Carbon
3 Organic Compounds
3 Hydrocarbons
3 Functional Groups
3 Nomenclature of Carbon
Compounds
3 Chemical Properties of
Carbon Compounds
3 Fuels and Flames
3 Some Important Carbon
Compounds
3 Soaps and Detergents
The number of electrons shared show the covalency of that
atom. Other atoms also exhibit similar type of bonding.
Examples
(i) Formation of Hydrogen Molecule
Atomic number of H = 1
It has 1 electron in its K shell and needs 1 more electron
to fill the K shell completely.
Thus, 2 H atoms share each of their electron to form a
molecule ofH
2
and thus, each H atom attains the nearest
noble gas configuration of helium (having two electrons
in its K shell). Valence electrons are depicted by using
dots or crosses.
The shared pair of electrons constitute a single bond
between the two H-atoms, which is represented by a
single line between the two atoms.
(ii) Formation of Chlorine Molecule
Atomic number of Cl = 17
Electronic configuration = 2 8 7
K L M
, ,
It has 7 electrons in its outermost shell and thus requires
1 more electron to fulfill its outermost shell. This is
achieved by sharing of 1 electron with another Cl atom,
forming a chlorine molecule ( ) Cl
2
.
(iii) Formation of Oxygen Molecule
Atomic number of O = 8
Electronic configuration = 2 6
K L
,
It requires 2 electrons to fulfill its octet and attain noble
gas configuration. This is achieved by sharing of 2
electrons of an another oxygen atom.
Here, a double bond between two oxygen atoms
forming an oxygen molecule represents the sharing of
4 electrons.
(iv) Formation of Nitrogen Molecule
Atomic number of N = 7
Electronic configuration = 2 5
K L
,
It needs 3 more electrons to attain noble gas
configuration. Thus, 2 nitrogen atoms share 3 each of
their electrons, forming a triple bond of nitrogen
molecule.
(v) Formation of Methane
Molecular formula CH
4
In methane molecule formation, one carbon shares 4
electrons with four different hydrogen atoms (one each
of different hydrogen atoms).
It shows carbon is tetravalent because it possesses four
valence electrons and hydrogen ismonovalent because it
has only one valence electron.
® Methane is a carbon compound and also called marsh gas It is
used as a fuel and a major component of CNG (Compressed
Natural Gas) andbiogas.
(vi) Formation of Ammonia and Water Molecule
Ammonia (NH )
3
2 Science Class 10th Term II
ll ne
Oxygenatoms
O
Sharedelectrons
== == O O
Oxygenmolecule
O O O
Covalent bonding in O
2
molecule
Nitrogenatoms
N
Sharedelectrons
== == N N
Nitrogenmolecule
N N N
Covalent bonding in N
2
molecule
H—H H H or
Single bond showingH
2
molecule
Cl Cl
Chlorineatoms
Cl Cl
Sharedelectrons
Cl—Cl
Chlorine
molecule
Covalent bonding in Cl
2
molecule
H
Hydrogenatoms
Sharedelectrons
H H H molecule
2
H
C H
== H—C—H
H
H
H
H
H
Formation of methane (CH
4
) molecule
N H
==N—H
H
H
H
H
Ammonia (NH
3
) molecule
Page 3


1
Carbonand
ItsCompounds
Carbon, a non-metal with atomic number 6 and mass number 12, occurs in
free as well as in combined form. All living creatures are based on it. Its amount in
the earth’s crust and in the atmosphere is quite meagre. In earth’s crust, there is
only 0.02% carbon which is present as minerals and in the atmosphere 0.03%
carbon is present in the form of carbon dioxide. Carbon thus forms a large
number of compounds with itself and with the atoms of other elements; some of
which are studied in this chapter.
Bonding in Carbon Compounds :
The Covalent Bond
Atomic number of carbon is 6, so there are 4 electrons in its outermost shell
and it needs to gain or loss 4 electrons in order to attain a stable configuration,
i.e., noble gas configuration.
The octet can be completed by following two ways
(i) It could lose 4 electrons and form C
4+
cation. But a massive amount of
energy is required to remove 4 electrons leaving behind a carbon cation
with 6 protons in its nucleus holding on to just two electrons.
(ii) It could gain 4 electrons and can formC
4-
anion. But for a nucleus having
6 protons, it would be difficult to hold on to 10 electrons, i.e., 4 extra
electrons.
In order to overcome this problem, carbon shares its valence electrons with its
other atoms or atoms of other elements.
These shared electrons belong to the outer shells of both the atoms and in this
way, both atoms attain the noble gas configuration. This type of bonding is called
covalent bonding. Thus, the bonds which are formed by the sharing of an electron
pair between two same or different atoms are known as covalent bonds.
ll ne
3 Bonding in Carbon
Compounds: The Covalent
Bond
3 Allotropes of Carbon
3 Versatile Nature of
Carbon
3 Organic Compounds
3 Hydrocarbons
3 Functional Groups
3 Nomenclature of Carbon
Compounds
3 Chemical Properties of
Carbon Compounds
3 Fuels and Flames
3 Some Important Carbon
Compounds
3 Soaps and Detergents
The number of electrons shared show the covalency of that
atom. Other atoms also exhibit similar type of bonding.
Examples
(i) Formation of Hydrogen Molecule
Atomic number of H = 1
It has 1 electron in its K shell and needs 1 more electron
to fill the K shell completely.
Thus, 2 H atoms share each of their electron to form a
molecule ofH
2
and thus, each H atom attains the nearest
noble gas configuration of helium (having two electrons
in its K shell). Valence electrons are depicted by using
dots or crosses.
The shared pair of electrons constitute a single bond
between the two H-atoms, which is represented by a
single line between the two atoms.
(ii) Formation of Chlorine Molecule
Atomic number of Cl = 17
Electronic configuration = 2 8 7
K L M
, ,
It has 7 electrons in its outermost shell and thus requires
1 more electron to fulfill its outermost shell. This is
achieved by sharing of 1 electron with another Cl atom,
forming a chlorine molecule ( ) Cl
2
.
(iii) Formation of Oxygen Molecule
Atomic number of O = 8
Electronic configuration = 2 6
K L
,
It requires 2 electrons to fulfill its octet and attain noble
gas configuration. This is achieved by sharing of 2
electrons of an another oxygen atom.
Here, a double bond between two oxygen atoms
forming an oxygen molecule represents the sharing of
4 electrons.
(iv) Formation of Nitrogen Molecule
Atomic number of N = 7
Electronic configuration = 2 5
K L
,
It needs 3 more electrons to attain noble gas
configuration. Thus, 2 nitrogen atoms share 3 each of
their electrons, forming a triple bond of nitrogen
molecule.
(v) Formation of Methane
Molecular formula CH
4
In methane molecule formation, one carbon shares 4
electrons with four different hydrogen atoms (one each
of different hydrogen atoms).
It shows carbon is tetravalent because it possesses four
valence electrons and hydrogen ismonovalent because it
has only one valence electron.
® Methane is a carbon compound and also called marsh gas It is
used as a fuel and a major component of CNG (Compressed
Natural Gas) andbiogas.
(vi) Formation of Ammonia and Water Molecule
Ammonia (NH )
3
2 Science Class 10th Term II
ll ne
Oxygenatoms
O
Sharedelectrons
== == O O
Oxygenmolecule
O O O
Covalent bonding in O
2
molecule
Nitrogenatoms
N
Sharedelectrons
== == N N
Nitrogenmolecule
N N N
Covalent bonding in N
2
molecule
H—H H H or
Single bond showingH
2
molecule
Cl Cl
Chlorineatoms
Cl Cl
Sharedelectrons
Cl—Cl
Chlorine
molecule
Covalent bonding in Cl
2
molecule
H
Hydrogenatoms
Sharedelectrons
H H H molecule
2
H
C H
== H—C—H
H
H
H
H
H
Formation of methane (CH
4
) molecule
N H
==N—H
H
H
H
H
Ammonia (NH
3
) molecule
Water (H O)
2
(vii) Formation of Carbon Dioxide ( ) CO
2
Atomic number of C = 6
Electronic configuration = 2 4
K L
Atomic number of O = 8
Electronic configuration = 2 6
K L
Thus, they complete their octet as
•
•
• •
•
•
×
×
×
×
•
•
• •
•
•
• •
• •
•
•
×
×
×
×
•
•
• •
• •
?? O C O O C O
or O C O == ==
(viii) Formation of Sulphur Molecule (S
8
)
Atomic number of sulphur = 16
Electronic configuration = 2 8 6
K L M
So, the valency of each S atom is 2.
Properties of Covalent Compounds
Covalently bonded molecules are called covalent
compounds.
Their important properties are
? Their constituents are molecules, not ions.
? They have strong bonds within the molecule but
intermolecular forces are weak, which is responsible for
the low melting and boiling points of these compounds
(graphite and diamond are exceptions of this).
? In these compounds, electrons are only shared and no
charged particle is formed, therefore, these compounds
are the bad conductors of electricity due to the absence
of free electrons or ions. However, graphite is an
exception of it, which is a good conductor of electricity.
? These compounds are generally insoluble in water but
some which are capable to form H-bond are soluble in
water.
Allotropes of Carbon
Some chemical elements can exist in two or more
different forms, which differ in arrangement of atoms and in
number of atoms but are chemically same. These are known
as allotropes and this phenomenon is known as allotropism.
For example, Carbon exists in several allotropic forms like
diamond, graphite, buckminster fullerene, coal, charcoal,
etc. The former three are crystalline while others are
amorphous form.
Diamond
General Properties
General properties of diamond are
? It is a colourless transparent substance with
extraordinary brilliance due to its high refractive index.
? It is quite heavy.
? It is extremely hard (hardest natural substance known).
? It does not conduct electricity (because of the absence of
free electrons).
? It has high thermal conductivity and high melting
point.
? It burns on strong heating to form carbon dioxide.
Structure
It is a giant molecule of carbon atoms in which each
carbon atom is linked to four other carbon atoms by strong
covalent bonds forming a rigid three-dimensional network
structure, which is responsible for its hardness. Moreover, a
lot of energy is required to break the network of strong
covalent bonds in the diamond crystal, thus its melting
point is very high.
Carbon and Its Compounds 3
ll ne
S
S
S
S
S
S
S
S
S
S
S
S
S
S S
S
Crownshaped
S molecule
8
O
or
H
H
H
H
== H—O—H
O
Water( ) HO
2
molecule
Diamond structure
Page 4


1
Carbonand
ItsCompounds
Carbon, a non-metal with atomic number 6 and mass number 12, occurs in
free as well as in combined form. All living creatures are based on it. Its amount in
the earth’s crust and in the atmosphere is quite meagre. In earth’s crust, there is
only 0.02% carbon which is present as minerals and in the atmosphere 0.03%
carbon is present in the form of carbon dioxide. Carbon thus forms a large
number of compounds with itself and with the atoms of other elements; some of
which are studied in this chapter.
Bonding in Carbon Compounds :
The Covalent Bond
Atomic number of carbon is 6, so there are 4 electrons in its outermost shell
and it needs to gain or loss 4 electrons in order to attain a stable configuration,
i.e., noble gas configuration.
The octet can be completed by following two ways
(i) It could lose 4 electrons and form C
4+
cation. But a massive amount of
energy is required to remove 4 electrons leaving behind a carbon cation
with 6 protons in its nucleus holding on to just two electrons.
(ii) It could gain 4 electrons and can formC
4-
anion. But for a nucleus having
6 protons, it would be difficult to hold on to 10 electrons, i.e., 4 extra
electrons.
In order to overcome this problem, carbon shares its valence electrons with its
other atoms or atoms of other elements.
These shared electrons belong to the outer shells of both the atoms and in this
way, both atoms attain the noble gas configuration. This type of bonding is called
covalent bonding. Thus, the bonds which are formed by the sharing of an electron
pair between two same or different atoms are known as covalent bonds.
ll ne
3 Bonding in Carbon
Compounds: The Covalent
Bond
3 Allotropes of Carbon
3 Versatile Nature of
Carbon
3 Organic Compounds
3 Hydrocarbons
3 Functional Groups
3 Nomenclature of Carbon
Compounds
3 Chemical Properties of
Carbon Compounds
3 Fuels and Flames
3 Some Important Carbon
Compounds
3 Soaps and Detergents
The number of electrons shared show the covalency of that
atom. Other atoms also exhibit similar type of bonding.
Examples
(i) Formation of Hydrogen Molecule
Atomic number of H = 1
It has 1 electron in its K shell and needs 1 more electron
to fill the K shell completely.
Thus, 2 H atoms share each of their electron to form a
molecule ofH
2
and thus, each H atom attains the nearest
noble gas configuration of helium (having two electrons
in its K shell). Valence electrons are depicted by using
dots or crosses.
The shared pair of electrons constitute a single bond
between the two H-atoms, which is represented by a
single line between the two atoms.
(ii) Formation of Chlorine Molecule
Atomic number of Cl = 17
Electronic configuration = 2 8 7
K L M
, ,
It has 7 electrons in its outermost shell and thus requires
1 more electron to fulfill its outermost shell. This is
achieved by sharing of 1 electron with another Cl atom,
forming a chlorine molecule ( ) Cl
2
.
(iii) Formation of Oxygen Molecule
Atomic number of O = 8
Electronic configuration = 2 6
K L
,
It requires 2 electrons to fulfill its octet and attain noble
gas configuration. This is achieved by sharing of 2
electrons of an another oxygen atom.
Here, a double bond between two oxygen atoms
forming an oxygen molecule represents the sharing of
4 electrons.
(iv) Formation of Nitrogen Molecule
Atomic number of N = 7
Electronic configuration = 2 5
K L
,
It needs 3 more electrons to attain noble gas
configuration. Thus, 2 nitrogen atoms share 3 each of
their electrons, forming a triple bond of nitrogen
molecule.
(v) Formation of Methane
Molecular formula CH
4
In methane molecule formation, one carbon shares 4
electrons with four different hydrogen atoms (one each
of different hydrogen atoms).
It shows carbon is tetravalent because it possesses four
valence electrons and hydrogen ismonovalent because it
has only one valence electron.
® Methane is a carbon compound and also called marsh gas It is
used as a fuel and a major component of CNG (Compressed
Natural Gas) andbiogas.
(vi) Formation of Ammonia and Water Molecule
Ammonia (NH )
3
2 Science Class 10th Term II
ll ne
Oxygenatoms
O
Sharedelectrons
== == O O
Oxygenmolecule
O O O
Covalent bonding in O
2
molecule
Nitrogenatoms
N
Sharedelectrons
== == N N
Nitrogenmolecule
N N N
Covalent bonding in N
2
molecule
H—H H H or
Single bond showingH
2
molecule
Cl Cl
Chlorineatoms
Cl Cl
Sharedelectrons
Cl—Cl
Chlorine
molecule
Covalent bonding in Cl
2
molecule
H
Hydrogenatoms
Sharedelectrons
H H H molecule
2
H
C H
== H—C—H
H
H
H
H
H
Formation of methane (CH
4
) molecule
N H
==N—H
H
H
H
H
Ammonia (NH
3
) molecule
Water (H O)
2
(vii) Formation of Carbon Dioxide ( ) CO
2
Atomic number of C = 6
Electronic configuration = 2 4
K L
Atomic number of O = 8
Electronic configuration = 2 6
K L
Thus, they complete their octet as
•
•
• •
•
•
×
×
×
×
•
•
• •
•
•
• •
• •
•
•
×
×
×
×
•
•
• •
• •
?? O C O O C O
or O C O == ==
(viii) Formation of Sulphur Molecule (S
8
)
Atomic number of sulphur = 16
Electronic configuration = 2 8 6
K L M
So, the valency of each S atom is 2.
Properties of Covalent Compounds
Covalently bonded molecules are called covalent
compounds.
Their important properties are
? Their constituents are molecules, not ions.
? They have strong bonds within the molecule but
intermolecular forces are weak, which is responsible for
the low melting and boiling points of these compounds
(graphite and diamond are exceptions of this).
? In these compounds, electrons are only shared and no
charged particle is formed, therefore, these compounds
are the bad conductors of electricity due to the absence
of free electrons or ions. However, graphite is an
exception of it, which is a good conductor of electricity.
? These compounds are generally insoluble in water but
some which are capable to form H-bond are soluble in
water.
Allotropes of Carbon
Some chemical elements can exist in two or more
different forms, which differ in arrangement of atoms and in
number of atoms but are chemically same. These are known
as allotropes and this phenomenon is known as allotropism.
For example, Carbon exists in several allotropic forms like
diamond, graphite, buckminster fullerene, coal, charcoal,
etc. The former three are crystalline while others are
amorphous form.
Diamond
General Properties
General properties of diamond are
? It is a colourless transparent substance with
extraordinary brilliance due to its high refractive index.
? It is quite heavy.
? It is extremely hard (hardest natural substance known).
? It does not conduct electricity (because of the absence of
free electrons).
? It has high thermal conductivity and high melting
point.
? It burns on strong heating to form carbon dioxide.
Structure
It is a giant molecule of carbon atoms in which each
carbon atom is linked to four other carbon atoms by strong
covalent bonds forming a rigid three-dimensional network
structure, which is responsible for its hardness. Moreover, a
lot of energy is required to break the network of strong
covalent bonds in the diamond crystal, thus its melting
point is very high.
Carbon and Its Compounds 3
ll ne
S
S
S
S
S
S
S
S
S
S
S
S
S
S S
S
Crownshaped
S molecule
8
O
or
H
H
H
H
== H—O—H
O
Water( ) HO
2
molecule
Diamond structure
Uses
Uses of diamond are
? Due to its hardness it is used in knives for cutting marble,
granite and glass.
? It is used for the purpose of ornaments studded as precious
stones.
? It is used as an abrasive and for polishing hard surface.
? Dies made from diamond are used for drawing wires from
the metals.
® Diamond can be prepared artificially by subjecting pure carbon to
very highpressureand temperature. Thesesyntheticdiamonds are
small butareotherwiseindistinguishablefromnatural diamonds.
Graphite
General Properties
General properties of graphite are
? It is a greyish black opaque substance.
? It is lighter than diamond, feels soft and slippery to touch.
? It is a good conductor of electricity (due to the presence of
free electrons) but bad conductor of heat.
? It burns on strong heating to form carbon dioxide.
Structure
A graphite crystal consists of layers of carbon atoms or
sheets of carbon atoms. Each carbon atom in a graphite layer is
joined to three other carbon atoms by strong covalent bonds to
form flat hexagonal rings. However, the fourth electron of each
carbon atom is free which makes it good conductor of
electricity. The various layers of carbon atoms in graphite are
held together by weak van der Waals’ forces so these can slide
over one another.
Uses
Uses of graphite are
? It is used as a powdered lubricant for the parts of
machinery.
? It is used for making electrodes of cells.
? It is used for making lead for pencils as it can mark paper
black. It is therefore called black lead or plumbago.
? It can withstand high temperature so used for making
crucibles to melt substances with high melting points and
tiles on the nose cone of space shuttle.
Fullerenes
These are recently prepared allotropic forms of carbon
and were prepared first time by HW Kroto, Smalley and
RobertCurt by the action of laser beam on the vapours of
graphite. Most commonly known fullerene contains 60 C
atoms(C )
60
with smaller proportion ofC
70
and traces of
compounds containing even upto 370 carbon atoms.
C
60
fullerene was named buckminsterfullerene after
the American architect Buckminster Fuller because its
structure resembled with the framework of domeshaped
halls designed by Fuller for the large international
exhibitions.
Properties
Properties of fullerenes are
? These are dark solids at room temperature.
? These are neither too hard nor too soft.
? These are the purest allotrophic forms of carbon
because of the absence of free valencies or surface
bonds.
? On burning, these produce only carbon dioxide gas.
Other properties of fullerene are still being
investigated.
Structure
C
60
is a football shaped spherical molecule in
which 60 C atoms are arranged in interlocking hexagonal
and pentagonal rings of carbon atoms. OneC
60
molecule
contains 20 hexagons and 12 pentagons of carbon atoms.
Uses
Uses of fullerene are
? In pure form, these behave as insulators. However,
these can be converted into semiconductors under
suitable conditions.
? C O
60
, a molecule formed when C
60
traps O atoms, is
used in cancer as well as AIDS therapy.
? In small amounts, these are used to catalyse the
photochemical refining in industry.
4 Science Class 10th Term II
ll ne
Graphite Structure
Buckminster fullerene (C
60
) Structure
Page 5


1
Carbonand
ItsCompounds
Carbon, a non-metal with atomic number 6 and mass number 12, occurs in
free as well as in combined form. All living creatures are based on it. Its amount in
the earth’s crust and in the atmosphere is quite meagre. In earth’s crust, there is
only 0.02% carbon which is present as minerals and in the atmosphere 0.03%
carbon is present in the form of carbon dioxide. Carbon thus forms a large
number of compounds with itself and with the atoms of other elements; some of
which are studied in this chapter.
Bonding in Carbon Compounds :
The Covalent Bond
Atomic number of carbon is 6, so there are 4 electrons in its outermost shell
and it needs to gain or loss 4 electrons in order to attain a stable configuration,
i.e., noble gas configuration.
The octet can be completed by following two ways
(i) It could lose 4 electrons and form C
4+
cation. But a massive amount of
energy is required to remove 4 electrons leaving behind a carbon cation
with 6 protons in its nucleus holding on to just two electrons.
(ii) It could gain 4 electrons and can formC
4-
anion. But for a nucleus having
6 protons, it would be difficult to hold on to 10 electrons, i.e., 4 extra
electrons.
In order to overcome this problem, carbon shares its valence electrons with its
other atoms or atoms of other elements.
These shared electrons belong to the outer shells of both the atoms and in this
way, both atoms attain the noble gas configuration. This type of bonding is called
covalent bonding. Thus, the bonds which are formed by the sharing of an electron
pair between two same or different atoms are known as covalent bonds.
ll ne
3 Bonding in Carbon
Compounds: The Covalent
Bond
3 Allotropes of Carbon
3 Versatile Nature of
Carbon
3 Organic Compounds
3 Hydrocarbons
3 Functional Groups
3 Nomenclature of Carbon
Compounds
3 Chemical Properties of
Carbon Compounds
3 Fuels and Flames
3 Some Important Carbon
Compounds
3 Soaps and Detergents
The number of electrons shared show the covalency of that
atom. Other atoms also exhibit similar type of bonding.
Examples
(i) Formation of Hydrogen Molecule
Atomic number of H = 1
It has 1 electron in its K shell and needs 1 more electron
to fill the K shell completely.
Thus, 2 H atoms share each of their electron to form a
molecule ofH
2
and thus, each H atom attains the nearest
noble gas configuration of helium (having two electrons
in its K shell). Valence electrons are depicted by using
dots or crosses.
The shared pair of electrons constitute a single bond
between the two H-atoms, which is represented by a
single line between the two atoms.
(ii) Formation of Chlorine Molecule
Atomic number of Cl = 17
Electronic configuration = 2 8 7
K L M
, ,
It has 7 electrons in its outermost shell and thus requires
1 more electron to fulfill its outermost shell. This is
achieved by sharing of 1 electron with another Cl atom,
forming a chlorine molecule ( ) Cl
2
.
(iii) Formation of Oxygen Molecule
Atomic number of O = 8
Electronic configuration = 2 6
K L
,
It requires 2 electrons to fulfill its octet and attain noble
gas configuration. This is achieved by sharing of 2
electrons of an another oxygen atom.
Here, a double bond between two oxygen atoms
forming an oxygen molecule represents the sharing of
4 electrons.
(iv) Formation of Nitrogen Molecule
Atomic number of N = 7
Electronic configuration = 2 5
K L
,
It needs 3 more electrons to attain noble gas
configuration. Thus, 2 nitrogen atoms share 3 each of
their electrons, forming a triple bond of nitrogen
molecule.
(v) Formation of Methane
Molecular formula CH
4
In methane molecule formation, one carbon shares 4
electrons with four different hydrogen atoms (one each
of different hydrogen atoms).
It shows carbon is tetravalent because it possesses four
valence electrons and hydrogen ismonovalent because it
has only one valence electron.
® Methane is a carbon compound and also called marsh gas It is
used as a fuel and a major component of CNG (Compressed
Natural Gas) andbiogas.
(vi) Formation of Ammonia and Water Molecule
Ammonia (NH )
3
2 Science Class 10th Term II
ll ne
Oxygenatoms
O
Sharedelectrons
== == O O
Oxygenmolecule
O O O
Covalent bonding in O
2
molecule
Nitrogenatoms
N
Sharedelectrons
== == N N
Nitrogenmolecule
N N N
Covalent bonding in N
2
molecule
H—H H H or
Single bond showingH
2
molecule
Cl Cl
Chlorineatoms
Cl Cl
Sharedelectrons
Cl—Cl
Chlorine
molecule
Covalent bonding in Cl
2
molecule
H
Hydrogenatoms
Sharedelectrons
H H H molecule
2
H
C H
== H—C—H
H
H
H
H
H
Formation of methane (CH
4
) molecule
N H
==N—H
H
H
H
H
Ammonia (NH
3
) molecule
Water (H O)
2
(vii) Formation of Carbon Dioxide ( ) CO
2
Atomic number of C = 6
Electronic configuration = 2 4
K L
Atomic number of O = 8
Electronic configuration = 2 6
K L
Thus, they complete their octet as
•
•
• •
•
•
×
×
×
×
•
•
• •
•
•
• •
• •
•
•
×
×
×
×
•
•
• •
• •
?? O C O O C O
or O C O == ==
(viii) Formation of Sulphur Molecule (S
8
)
Atomic number of sulphur = 16
Electronic configuration = 2 8 6
K L M
So, the valency of each S atom is 2.
Properties of Covalent Compounds
Covalently bonded molecules are called covalent
compounds.
Their important properties are
? Their constituents are molecules, not ions.
? They have strong bonds within the molecule but
intermolecular forces are weak, which is responsible for
the low melting and boiling points of these compounds
(graphite and diamond are exceptions of this).
? In these compounds, electrons are only shared and no
charged particle is formed, therefore, these compounds
are the bad conductors of electricity due to the absence
of free electrons or ions. However, graphite is an
exception of it, which is a good conductor of electricity.
? These compounds are generally insoluble in water but
some which are capable to form H-bond are soluble in
water.
Allotropes of Carbon
Some chemical elements can exist in two or more
different forms, which differ in arrangement of atoms and in
number of atoms but are chemically same. These are known
as allotropes and this phenomenon is known as allotropism.
For example, Carbon exists in several allotropic forms like
diamond, graphite, buckminster fullerene, coal, charcoal,
etc. The former three are crystalline while others are
amorphous form.
Diamond
General Properties
General properties of diamond are
? It is a colourless transparent substance with
extraordinary brilliance due to its high refractive index.
? It is quite heavy.
? It is extremely hard (hardest natural substance known).
? It does not conduct electricity (because of the absence of
free electrons).
? It has high thermal conductivity and high melting
point.
? It burns on strong heating to form carbon dioxide.
Structure
It is a giant molecule of carbon atoms in which each
carbon atom is linked to four other carbon atoms by strong
covalent bonds forming a rigid three-dimensional network
structure, which is responsible for its hardness. Moreover, a
lot of energy is required to break the network of strong
covalent bonds in the diamond crystal, thus its melting
point is very high.
Carbon and Its Compounds 3
ll ne
S
S
S
S
S
S
S
S
S
S
S
S
S
S S
S
Crownshaped
S molecule
8
O
or
H
H
H
H
== H—O—H
O
Water( ) HO
2
molecule
Diamond structure
Uses
Uses of diamond are
? Due to its hardness it is used in knives for cutting marble,
granite and glass.
? It is used for the purpose of ornaments studded as precious
stones.
? It is used as an abrasive and for polishing hard surface.
? Dies made from diamond are used for drawing wires from
the metals.
® Diamond can be prepared artificially by subjecting pure carbon to
very highpressureand temperature. Thesesyntheticdiamonds are
small butareotherwiseindistinguishablefromnatural diamonds.
Graphite
General Properties
General properties of graphite are
? It is a greyish black opaque substance.
? It is lighter than diamond, feels soft and slippery to touch.
? It is a good conductor of electricity (due to the presence of
free electrons) but bad conductor of heat.
? It burns on strong heating to form carbon dioxide.
Structure
A graphite crystal consists of layers of carbon atoms or
sheets of carbon atoms. Each carbon atom in a graphite layer is
joined to three other carbon atoms by strong covalent bonds to
form flat hexagonal rings. However, the fourth electron of each
carbon atom is free which makes it good conductor of
electricity. The various layers of carbon atoms in graphite are
held together by weak van der Waals’ forces so these can slide
over one another.
Uses
Uses of graphite are
? It is used as a powdered lubricant for the parts of
machinery.
? It is used for making electrodes of cells.
? It is used for making lead for pencils as it can mark paper
black. It is therefore called black lead or plumbago.
? It can withstand high temperature so used for making
crucibles to melt substances with high melting points and
tiles on the nose cone of space shuttle.
Fullerenes
These are recently prepared allotropic forms of carbon
and were prepared first time by HW Kroto, Smalley and
RobertCurt by the action of laser beam on the vapours of
graphite. Most commonly known fullerene contains 60 C
atoms(C )
60
with smaller proportion ofC
70
and traces of
compounds containing even upto 370 carbon atoms.
C
60
fullerene was named buckminsterfullerene after
the American architect Buckminster Fuller because its
structure resembled with the framework of domeshaped
halls designed by Fuller for the large international
exhibitions.
Properties
Properties of fullerenes are
? These are dark solids at room temperature.
? These are neither too hard nor too soft.
? These are the purest allotrophic forms of carbon
because of the absence of free valencies or surface
bonds.
? On burning, these produce only carbon dioxide gas.
Other properties of fullerene are still being
investigated.
Structure
C
60
is a football shaped spherical molecule in
which 60 C atoms are arranged in interlocking hexagonal
and pentagonal rings of carbon atoms. OneC
60
molecule
contains 20 hexagons and 12 pentagons of carbon atoms.
Uses
Uses of fullerene are
? In pure form, these behave as insulators. However,
these can be converted into semiconductors under
suitable conditions.
? C O
60
, a molecule formed when C
60
traps O atoms, is
used in cancer as well as AIDS therapy.
? In small amounts, these are used to catalyse the
photochemical refining in industry.
4 Science Class 10th Term II
ll ne
Graphite Structure
Buckminster fullerene (C
60
) Structure
Versatile Nature of Carbon
The estimate number of carbon compounds known
today is about three million. But now the question is, which
property or properties of carbon is/are responsible for the
formation of such a large number of carbon compounds.
Two characteristic properties of carbon are responsible
for this.
These properties are
(i) Catenation (ii) Tetravalency
(i)Catenation
Carbon atoms have a unique ability to form bonds
(single, double as well as triple) with other carbon atoms to
form large molecules. These can arrange themselves in
straight chain, in branched chains or in the form of rings.
This property of self linking of carbons atom through
covalent bonds to form straight chains or cyclic rings of
carbon atoms is called catenation.
Carbon exhibits the property of catenation to maximum
extent due to large C-C bond energy and hence, forms large
number of compounds.
(ii)Tetravalency
Due to the valency of four, carbon is capable of bonding
or pairing with four other carbon atoms or with the atoms of
some other monovalent elements. It also forms compounds
with oxygen, nitrogen, sulphur, hydrogen and many other
elements. This gives rise to compounds with specific
properties which depend on the element other than carbon
present in the molecule.
Bonds which carbon forms with other elements are very
strong thus, making these compounds very stable. The main
reason for such strong bond formation is the small size of
carbon. As a result, the shared pair of electrons are tightly
held by the nucleus.
® The strength of bond decreases with increase in the size of
atoms.
Organic Compounds
The compounds of carbon except its oxides, carbonates
and hydrogen carbonate salts, are known as organic
compounds. These compounds were initially extracted from
natural substances and was believed that some vital force was
necessary for the synthesis of these compounds (vital force
theory).
In 1828, synthesis of urea, by German chemistFriedrich
Wohler accidently when he was trying to prepare
ammonium cyanate by heating ammonium sulphate and
potassium cyanate, gave death below to this theory.
(NH ) SO 2KCNO
4 2 4
Ammonium sulphate
Potassium cyanate
+ ??
?
2NH CNO K SO
4 2 4
Ammonium
cyanate
Potassium
sulphate
+
NH CNO NH CONH
4 2
Ammonium
cyanate
(Rearrangement)
??????
?
2
Urea
Synthesis of acetic acid from its elements by Kolbe in
1845 also disproved the vital force theory.
Carbon and Its Compounds 5
ll ne
1. What is the covalency of nitrogen atom in nitrogen
gas?
2. Name the two properties of carbon which makes it
different from other elements.
3. Why are covalent compounds bad conductor of
electricity?
4. Graphite is a covalent molecule but a good
conductor of electricity. Explain why?
5. Why are fullerene so called?
Check oint1
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