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INDIAN CENTRAL SCHOOL, KUWAIT

CLASS: X SUBJECT: CHEMISTRY

Slot-7 CHAPTER-4 CARBON AND ITS COMPOUNDS

The symbol of carbon is C and atomic number is 6. Electronic configuration is 2,4. Carbon has 4

valence electrons and needs to gain or lose 4 electrons to attain stable noble- gas configuration.

Q. State the reason why carbon can neither form C4+

cations nor C4-

anions, but form covalent

bonds.

Ans: a) When carbon loses 4 electrons, it becomes C4+

cation.

C → C4+

+ 4 electrons.

(2, 4) (2)

But large amount of energy is needed to remove 4 electrons leaving a C4+

ion

with 6 protons in its nucleus holding on to just 2 electrons.

b) Carbon gains 4 electrons to become C4-

anion.

C + 4 electrons → C4-

(2,4) (2,8).

This is not possible because 6 protons cannot hold 10 electrons. Therefore in order to overcome

this, carbon can share 4 valence electrons with other carbon atoms or atoms of other elements to

form covalent bonds.

Formation of covalent bond: A covalent bond is formed by the mutual sharing of electrons

between atoms to acquire stable electronic configuration.

Types of covalent bonds:

a) Single covalent bond: A covalent bond which is formed by the sharing of single pair of

electrons between two atoms. It is represented by putting a short line(-) between two atoms.

Examples:

i) Hydrogen molecule : Hydrogen atom has one electron in its valence shell. It share its one

electron with other hydrogen atom to form a single covalent bond to form hydrogen molecule.

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ii) Chlorine molecule: In the formation of chlorine molecule, each Cl atom share a pair of

electrons to form a single covalent bond.

b) Double covalent bond: A bond which is formed by the sharing of two pairs of electrons

between two atoms called double covalent bond. It is represented by putting two short lines =

between the atoms.

Examples: i) Oxygen molecule: Oxygen atom has 6 valence electrons in the valence shell. It

shares its 2 electrons with other oxygen atom to form a double covalent bond.

ii) Carbon dioxide molecule: In the formation of Carbon dioxide, each oxygen atom share 2 pairs

of electrons with carbon atom forms double covalent bonds.

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c) Triple covalent bond: A bond which is formed by the sharing of 3 pairs of electrons between

the atoms. It is represented by putting 3 short lines between the two atoms.

Example:

Formation of Nitrogen molecule ( N2) : Nitrogen atom has 5 valence electrons in its valence

shell. It shares its 3 electrons with other nitrogen atom to form a triple covalent bond.

Formation of water molecule: In water molecule, the oxygen atom has 6 valence electrons in its

valence shell. It shares its two electrons with two hydrogen atoms to form two O – H bonds.

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Formation of Ammonia molecule (NH3): Nitrogen atom has 5 valence electrons in its valence

shell. It shares its 3 electrons with 3 hydrogen atoms to form three N – H bonds.

Formation of methane molecule (CH4) : Carbon atom has 4 valence electrons in its valence

shell. It shares its 4 electrons with 4 hydrogen atoms to form four C – H single covalent bonds

OR

Characteristics of covalent compounds

1. State of existence: Covalent compounds are formed by the mutual sharing of electrons. There

is no transfer of electrons from one atom to another. Hence there is no ion formation. The

compounds exist as molecules and not as ions. Since there is no inter ionic force of attraction,

covalent compounds exists in solid, liquid and gaseous state.

2. M.P and B.P : They have low M.P and B.P due to weak intermolecular force of attraction

between the molecules. Less amount of energy is required to overcome these force of attraction

between the molecules.

3. Electrical conductivity : They are poor conductors of electricity because they do not contain

free electrons or ions.

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4. Solubility: They are insoluble in water but soluble in non-polar solvents like ether, CCl4…..

Q: What are the differences between ionic compounds and co-valent compounds?

Questions (Reader pg 61)

1. What would be the electron dot structure of carbon dioxide which has the formula CO2.

2. What would be the electron dot structure of a molecule of sulphur which is made up of 8

atoms of sulphur

3. Why do covalent compounds have low M.P and B.P? (Refer the notes)

4. Why do covalent compounds are poor conductors of electricity? (Refer the notes)

5. Write the differences between diamond and graphite.

Ans: Graphite i) Each carbon atom is joined to 3 other carbon atoms.

ii) The carbon atoms form flat hexagonal layers.

iii) Graphite is soft and slippery.

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iv) It conduct electricity.

Diamond: i) Each carbon atom is joined to 4 other carbon atoms.

ii) The carbon atoms together form a three dimensional structure.

iii) It is a hardest substance.

iv) It does not conduct electricity.( every carbon atom forms a covalent bond, which means that

there are no free electrons)

Versatile nature of Carbon:

The Versatile nature of Carbon is due to the following two important properties.

1. Catenation: The ability of carbon to combine with another carbon atom to form long chains,

branched chains or even closed rings is known as catenation.

-C-C-C-C- C-C-C- Long straight chain

-C-C-C-C-C –C- - Branched chain

C

Closed ring

The catenation property is because of strong covalent bond between carbon atoms. This strong

covalent bond between carbon atoms is due to its small size which enables the nucleus to hold on

to the shared pair of electrons strongly.

2. Tetravalency: The valency of carbon is 4. Hence it can form 4 covalent bonds with other

carbon atoms or with other atoms like oxygen, hydrogen, nitrogen etc.

HYDROCARBONS:

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The compounds made of only Carbon and Hydrogen elements are known as hydrocarbons.

Depending on the nature of bond between the carbon atoms, they are of two types. (i) Saturated

hydrocarbons and (ii) Unsaturated hydrocarbons.

1. Saturated hydrocarbons: Compounds of carbon having only single bonds between the

carbon atoms are called saturated hydrocarbons.

Eg: Alkanes

They all have single covalent bond between the atoms and their name ends with -ane

Eg: Ethane C2H6.

Three valencies of each carbon atom is unsatisfied. So each carbon is bonded to three H- atoms

giving the structure.

0r CH3-CH3

Electron dot structure of ethane:

2. Unsaturated hydrocarbons: Compounds of carbon having double bond or triple bond

between the carbon atoms are called unsaturated hydrocarbons

Example-Alkenes and Alkynes are unsaturated hydrocarbons

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Eg: i) Ethene: C2H4

Each carbon atom gets 2 Hydrogen atoms to give the structure

OR CH2=CH2

Electron dot structure of ethene:

ii) Ethyne C2H2

H C C H

Electron dot structure of ethyne:

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Unsaturated hydrocarbons are more reactive than saturated carbon compounds because of the

presence of double or triple bonds.

Cyclic Hydrocarbons:

These are some compounds have carbon atoms arranged in the form of closed rings. They are

known as cyclic hydrocarbons. These cyclic hydrocarbons may be saturated or unsaturated.

1. Saturated cyclic hydrocarbons: Here carbon atoms are joined by C-C single bond. Saturated

cyclic hydrocarbons are also called cyclo alkanes.

Eg: Cyclo hexane - C6H12

Structural formula

Electron dot structure of C6H12

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2. Unsaturated cyclic hydrocarbons: Unsaturated cyclic hydrocarbons contains at least one C-C

double bond.

Eg: Benzene - C6H6

Electron dot structure of Benzene( C6H6 )

The Unsaturated cyclic hydrocarbons like benzene are called also aromatic compounds.

Alkanes:

Saturated hydrocarbons are called alkanes. General formula of alkane is CnH2n+2 , where n is the

no.of carbon atoms in one molecule.

First member n = 1 , formula is CnH2n+2

C1 H4 = CH4

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Structure of methane

Second member n = 2 , formula is CnH2n+2 = C2H6

Structure of ethane

Alkenes:

Unsaturated hydrocarbons containing one or more double bonds between the carbon atoms are

known as alkenes. General formula is CnH2n

First member n = 2 , formula is CnH2n

= C2H4 –Ethene.

The simplest alkene is ethane. Its common name is ethylene.

Alkynes:

Unsaturated hydrocarbons containing one or more triple bonds between the carbon atoms are

known as alkenes. General formula is CnH2n-2

First member n = 2 , formula is CnH2n -2 = C2H2 – Ethyne.

The simplest alkyne is ethyne. Its common name is acetylene.

Formula and structure of saturated compounds of Carbon and Hydrogen:( copy from

reader pg.64 table 4.2)

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Structural isomers:

Compounds with identical molecular formula but different structures are called Structural

isomers.

Q: Write the structural formula of isomers of butane (C4H10)

Ans: 1. Normal butane

2. iso butane

Q: Write the structural formula of all the isomers of pentane (C5H12)

Ans: nor- pentane, iso-pentane and neo-pentane

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Q. What are isomers? Isomers of first three members of alkane series are not possible. Give

reason to justify this statement?

Ans: Isomers are compounds which have same molecular formula and different structural

formula.

In the first three members of alkane, branching is not possible. Therefore isomers are not

possible.

Characteristics of isomers:

i) They differ in structural formula.

ii) They differ in their M.P and B.P.

iii) They differ in solubility in same solvent.

Functional groups: The atoms like oxygen, nitrogen, sulphur, halogens etc. which will

replace one or more hydrogen atoms of hydrocarbon is known as heteroatom.

The heteroatom or a group of atoms which give a specific property to a carbon

compound irrespective of the length and the nature of carbon chain is known as functional

groups.

(Copy functional group table. 4.3 page-66)

Homologous series: A group of organic compounds which have the same functional group

in which successive members differ by a–CH2 group is known as homologous series.

eg: i) CH4 and C2H6 ii) C2H4 and C3H6.

i) Alkane series (CnH2n+2) ii) Alkene series(CnH2n) iii) Alkyne series(CnH2n-2)

Methane (CH4) Ethene (C2H4) Ethyne (C2H2)

Ethane (C2H6) Propene(C3H6) Propyne (C3H4)

Propane (C3H8) Butene (C4H8) Butyne (C4H6)

Butane (C4H10) Pentene (C5H10) Pentyne (C5H8)

iv) Alcohol homologous series(CnH2n+1OH)

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Methanol (CH3OH)

Ethanol (C2H5OH)

Propanol (C3H7OH)

Butanol (C4H9OH)

Characteristics of homologous series:

i) All the members of homologous series will have same functional group and can be

represented by same general formula.

ii) The successive members in a homologous series are differing by a–CH2 group.

iii) The compounds in a homologous series will have the same chemical properties but

different physical properties.

iv)All the members of a homologous series are prepared by the same methods.

Activity 4.2 (Reader pg 67 copy question from reader)

1.

Molecular formula Molecular mass Difference in mole

cular mass

Difference in

molecular formula

CH3OH 32u

C2H5OH 46u 14u -CH2

C2H5OH 46u

C3H7OH 60u 14u -CH2

C3H7OH,

C4H9OH

60u

74u

14u -CH2

2. Yes, all these have –OH functional group.

3. CH3OH C2H5OH ˂ C3H7 OH ˂ C4H9OH

4. i) If the functional group is a halogen like –Cl, the series become:

CH3Cl

C2H5Cl

C3H7Cl

C4H9Cl

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Aldehyde series:

H-CHO

CH3-CHO

C2H5-CHO

C3H7-CHO

C4H9-CHO

Ketone series:

CH3-CO-CH3

CH3-CH2-CO-CH3

Carboxylic acid:

H-COOH

CH3-COOH

CH3-CH2-COOH

CH3-CH2- CH2-COOH

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