INDIAN CENTRAL SCHOOL, KUWAIT CLASS: X SUBJECT: …
Transcript of INDIAN CENTRAL SCHOOL, KUWAIT CLASS: X SUBJECT: …
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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
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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