Carbon and its Compounds Notes CBSE

Class 10 Science Chapter 4

Bonding in Carbon: The Covalent bond, Electron dot structure, Physical properties of
organic compounds, Allotropes of Carbon.

Covalent Bond: The atomic number of carbon is 6. Its electronic configuration is 2, 4. It

requires, 4 electrons to achieve the inert gas electronic configuration. But carbon cannot
form an ionic bond

It could gain four electrons forming C cation. But it would be difficult for the nucleus with
4-

six protons to hold on to ten electrons.

It could lose four electrons forming C cations. But it requires a large amount of energy
4+

to remove four electrons.

Thus, carbon overcomes this problem by sharing of its valence electrons with other
carbon atoms or with atoms of other elements.

The bond formed by mutual sharing of electron pairs between two atoms in a molecule
is known as Covalent Bond.

Types of Covalent Bond:

 Single Covalent Bond: When a single pair of electrons are shared between two
atoms in a molecule. For example; F , Cl , H etc.
2 2 2

 Double Covalent Bond: When two pairs of electrons are shared between two
atoms in a molecule. For example; O , CO etc.
2 2

 Triple Covalent Bond: When three pairs of electrons are shared between two
atoms in a molecule. For example; N etc.
2

Electron Dot Structure: The electron dot structures provides a picture of bonding in
molecules in terms of the shared pairs of electrons and octet rule.

Formation of Hydrogen Molecule

Atomic number of Hydrogen = 1
Number of valence electrons = 1
Formation of CH Molecule
4

Atomic number of Carbon = 6 [2, 4]

Number of valence electrons = 4
Atomic number of Hydrogen = 1
Number of valence electrons = 1

Formation of CO Molecule
2

Atomic number of Carbon = 6 [2, 4]

Number of valence electrons = 4
Atomic number of Oxygen = 8 [2, 6]
Number of valence electrons = 6

Formation of H S Molecule
2

Atomic number of Sulphur = 16 [2, 8, 6]

Number of valence electrons = 6

Physical Properties of Organic Compounds

Most of the organic compounds have low boiling and melting point, due to the weak
force of attraction (i.e., the inter-molecular force of attraction) between these molecules.
Most carbon compounds are poor conductors of electricity, due to the absence of free
electrons and free ions.

Compounds M.P. (K) B.P. (K)

Acetic acid (CH COOH)

3 290 391

Chloroform (CHCl ) 3 209 334

Ethanol (CH CH OH)

3 2 156 351

Methane (CH ) 4 90 111

Allotropes of Carbon

Allotropy: The phenomenon in which the element exists in two or more different
physical states with similar chemical properties are called Allotropy.

Carbon has Three Main Allotropes

 Diamond: In this, carbon, an atom is bonded to four other atoms of carbon

forming three-dimensional structures. It is the hardest substance and an insulator.
It is used for drilling rocks and cutting. It is also used for making jewellery.
 Graphite: In this, each carbon atom is bonded to three other carbon atoms. It is a
good conductor of electricity and used as a lubricant.
 Buckminster Fullerene: It is an allotrope of the carbon-containing cluster of 60
carbon atoms joined together to form spherical molecules. It is dark solid at room
temperature.

Versatile nature of Carbon, Hydrocarbons, Isomerism, Homologous series, Functional

groups, Nomenclature of functional groups.
Versatile Nature of Carbon: The existence of such a large number of organic
compounds is due to the following nature of carbon,

 Catenation
 Tetravalent nature.

(i) Catenation: The self linking property of an element mainly carbon atom through
covalent bonds to form long straight, branched and rings of different sizes are called
Catenation.
This property is due to

 The small size of the carbon atom.

 The great strength of the carbon-carbon bond.

Carbon can also form stable multiple bonds (double or triple) with itself and with the
atoms of other elements.
Straight Chain

Branched Chain

Rings
(ii) Tetravalent Nature: Carbon has valency of four. It is capable of bonding with four
other atoms of carbon or some other heteroatoms with single covalent bond as well as
double or triple bond.

Hydrocarbons: Compounds of carbon and hydrogen are known as hydrocarbons.

For example; Methane (CH ), Ethane (C H ), Ethene (C H ), Ethyne (C H ) etc.
4 2 6 2 4 2 2

Saturated Hydrocarbon (Alkanes): General formula is C H . n 2n+2

n = number of carbon atoms.

In this, the carbon atoms are connected by only a single bond.
For example; Methane (CH ), Ethane (C H ) etc.
4 2 6
Unsaturated Hydrocarbons
Alkenes: General formula is C H , where n = number of carbon atoms.
n 2n

In this, the two carbon atoms are connected by double bond.

Alkynes: General formula is C H , where n = number of carbon atoms. In this, the two
n 2n-2

carbon atoms are connected by triple bond.

Electron Dot Structure of Hydrocarbons

Isomerism: Compounds having the same molecular formula but different structural
formula and properties are known as Isomers and this phenomenon is known as
Isomerism.
Structural Isomerism: Compounds having the same molecular formula but different
structures are called Structural isomers. Example: Isomers of butane (C H )
4 10

Homologous Series: Series of organic compounds having the same functional group
and chemical properties and successive members differ by a CH unit or 14 mass units
2

are known as Homologous series.

Homologous series of Alkanes, Alkenes and Alkynes

Characteristic of Homologous Series

 The successive members in homologous series differ by CH unit or 14 mass unit.

2

 Members of given homologous series have the same functional group.

 All the members of homologous series shows similar chemical properties.
 Functional Group: An atom or group of atoms present in a molecule which largely
determines its chemical properties are called Functional Group.

Nomenclature of Organic Compounds: It is difficult to remember millions of

compounds by their individual common name. Thus, to systematize the nomenclature of
organic compounds IUPAC (International Union of Pure and Applied Chemistry) has
given certain rule which is as follows:
1. Identify the Number of Carbon Atoms in the Compound

Word Root (-)

S. No Number of Carbon Atoms Single bond
(Suffix)

1. One carbon atoms (1-C) Meth + ane

2. Two carbon atoms (2-C) Eth + ane

3. Three carbon atoms (3-C) Prop + ane

4. Four carbon atoms (4-C) But + ane

5. Five carbon atoms (5-C) Pent + ane

6. Six carbon atoms (6-C) Hex + ane

2. Identify the functional group

S. No. Functional Group Prefix Suffix

1. Double bond (=) — ene

2. Triple bond (≡) — yne

3. Chlorine (—Cl) Chloro —

4. Bromine (—Br) Bromo —

5. Alcohol (-OH) — ol

6. Aldehyde (-CHO) — al
 7. Ketone (-CO-) — one

8. Carboxylic acid (-COOH) — oic acid

3. Name the Compounds By Following Order

Prefix + Word Root + Suffix
Chemical Properties of Carbon Compounds: The important chemical properties are
as follows:
1. Combustion: The complete combustion of carbon compounds in the air gives carbon
dioxide water, heat and light.
CH CH OH(l) + O (g) → CO (g) + H O(l) + Heat and light
3 2 2 2 2

Carbon burns in air or oxygen to give carbon dioxide and heat and light.
C(s) + O (g) → CO (g) + Heat and light
2 2

Saturated hydrocarbons burn with a blue flame in the presence of a sufficient supply of
air or oxygen.
CH (g) + 2O (g) → CO (g) + 2H O(l) + Heat and light
4 2 2 2

In presence of limited supply of air, saturated hydrocarbon forms a sooty flame.

Unsaturated hydrocarbons burn with a yellow smoky flame.

The gas and kerosene stove used at home has inlet for air so that, burnt to given clean
blue flame.
Due to presence of small amount of nitrogen and sulphur, coal and petroleum produces
carbon dioxide with oxides of nitrogen and sulphur which are major pollutant.

2. Oxidation: Oxidation of ethanol in presence of oxidizing agents gives ethanoic acid.

Oxidizing Agent: Some substances are capable of adding oxygen to others, are known
as Oxidising Agent.
Example: Alkaline KMnO (or KMnO —KOH)
4 4

Acidified K Cr O (or K Cr O —H SO )
2 2 7 2 2 7 2 4

KMnO – Potassium permanganate

4

K Cr O – Potassium dichromate
2 2 7

3. Addition Reaction: Addition of dihydrogen with unsaturated hydrocarbon in the

presence of catalysts such as nickel or platinum or palladium are known as
Hydrogenation (addition) reaction.

Catalyst: Substances that cause a reaction to occur or proceeds to different rate

without consuming in it are called a catalyst. For example; Ni, Pt, Pd, etc.

Process of converting vegetable oil into solid fat (vegetable ghee) is called
Hydrogenation of Oil.
Vegetable oil + H Undefined control sequence \xrightarrow Vegetable ghee
2

Vegetable fats are saturated fats which are harmful for health.

Vegetable oil containing unsaturated fatty acids are good for health.

4. Substitution Reaction: Replacement of one or more hydrogen atom of an organic

molecule by another atom or group of the atom is known as Substitution Reaction.