Carbon and its Compounds Notes – Class 10 Science

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Carbon and its Compounds

 

Carbon:

Introduction
Atomic Number: 6
Electronic Configuration: 2,4
Valence electrons: 4
Property: Non-Metal
Abundance: Carbon is the 4th most abundant substance in universe and 15th most abundant substance in the earth’s crust.
Compounds having carbon atoms among the components are known as carbon compounds. Previously, carbon compounds could only be obtained from a living source; hence they are also known as organic compounds.

Bonding In Carbon:

Covalent Bond

Bond formed by sharing of electrons is called covalent bond. Two of more atoms share electrons to make their configuration stable. In this type of bond, all the atoms have similar rights over shared electrons. Compounds which are formed because of covalent bond are called COVALNET COMPOUNDS.
Covalent bonds are of three types: Single, double and triple covalent bond.

 

Single Covalent Bond:  Single covalent bond is formed because of sharing of two electrons, one from each of the two atoms.

Formation of hydrogen molecule (H2)
Atomic Number of H = 1
Electronic configuration of H = 1
Valence electron of H = 1

Hydrogen forms a duet, to obtain stable configuration. This configuration is similar to helium (a noble gas).
Since, hydrogen has one electron in its valence shell, so it requires one more electron to form a duet. So, in the formation of hydrogen molecule; one electron from each of the hydrogen atoms is shared.

Formation of hydrogen chloride (HCl):

Valence electron of hydrogen = 1
Atomic number of chlorine = 17
Electronic configuration of chlorine: 2, 8, 7
Electrons in outermost orbit = 7
Valence electron = 7

Formation of chlorine molecule (Cl2):
Valence electron of chlorine = 7

Formation of water (H2O)
Valence electron of hydrogen = 1
Atomic number of oxygen = 8
Electronic configuration of oxygen = 2, 6
Valence electron = 6

Oxygen in water molecule completes stable configuration by the sharing one electron from each of the two hydrogen atoms.

Formation of Methane (CH4)
Valence electron of carbon = 4
Valence electron of hydrogen = 1

Formation of Ethane (C2H6):

Double covalent bond:
Double bond is formed by sharing of four electrons, two from each of the two atoms.

Formation of oxygen molecule (O2):
Valence electron of oxygen = 2

In the formation of oxygen molecule, two electrons are shared by each of the two oxygen atoms to complete their stable configuration.
In oxygen, the total number of shared electrons is four, two from each of the oxygen atoms. So a double covalent bond is formed.

Formation of Ethylene (C2H4):
Valence electron of carbon = 4
Valence electron of hydrogen = 1

Triple Covalent Bond: Triple covalent bond is formed because of the sharing of six electrons, three from each of the two atoms.

Formation of Nitrogen (N2):
Atomic number of nitrogen = 7
Electronic configuration of nitrogen = 2, 5
Valence electron = 5

In the formation of nitrogen, three electrons are shared by each of the nitrogen atoms. Thus one triple bond is formed because of the sharing of total six electrons.

Properties of Covalent Bond:

  • Intermolecular force is smaller.
  • Covalent bonds are weaker than ionic bond. As a result, covalent compounds have low melting and boiling points.
  • Covalent compounds are poor conductor of electricity as no charged particles are formed in covalent bond.
  • Since, carbon compounds are formed by the formation of covalent bond, so carbon compounds generally have low melting and boiling points and are poor conductor of electricity.

Organic Compounds

Initially, compounds of carbon could only be obtained from living sources and there was no way of synthesizing them. Hence, carbon compounds are also known as organic compounds. Carbon forms a large number of compounds. So far, formulae of about 3 million carbon compounds are known.

Cause of formation of such a large number of compounds by carbon:

  1. Carbon can form bonds with other carbon atoms. This property of carbon is known as CATENATION. Because of catenation, carbon can form a long chain; while making bond with other carbon atoms. Carbon can make single, double and triple bonds by catenation.
  2. Carbon can form bonds with other carbon atoms. This property of carbon is known as CATENATION. Because of catenation, carbon can form a long chain; while making bond with other carbon atoms. Carbon can make single, double and triple bonds by catenation.
  3. Carbon can form branched chain; along with straight chain; while combining with carbon atoms, i.e. because of the property of catenation.
  4. Example:

Carbon can also form bonds with other types of monovalent atoms; apart from carbon. Carbon can make long chain combining with other atoms also. For example; carbon can form bonds with oxygen, hydrogen, nitrogen, etc.
Carbon-carbon bonds are very stable, which makes the compounds of carbon stable.

 

Hydrocarbon:

(Hydrogen + Carbon = Hydrocarbon) Compounds formed because of the combination of hydrogen and carbon are known as hydrocarbons. There are two types of hydrocarbon, viz. saturated hydrocarbon and unsaturated hydrocarbon.

Saturated hydrocarbons: Hydrocarbons having single bonds are known as SATURATED HYDROCARBONS. Saturated hydrocarbons are known as ALKANE. These are also known as paraffin. Example: Methane, Ethane, Propane, etc.

Unsaturated hydrocarbon: Unsaturated hydrocarbons are of two types – Hydrocarbon with double bond and hydrocarbon with triple bond.
Hydrocarbon with double bond: Hydrocarbons having at least one double bond are known as ALKENE. Example: Ethylene, Propylene, Butylene, etc.
Hydrocarbon with triple bond: Hydrocarbons having at least one triple bond are known as ALKYNE. Example: Ethyne, Propyne, Butyne, etc.

 

Alkane

ALKANE: Hydrocarbons having only single bonds are known as alkane. These are saturated hydrocarbons. Alkane are also known as paraffin. The general formula of alkane is CnH2n+2

If C = 1, then; CnH2n+2 = C1H2×1+2 = CH4

Name of this compound is methane. It can be shown by following structural formula:

If C = 2, then; CnH2n+2 = C2H2×2+2 = C2H6

Name of this compound is ethane. It can be shown by following structural formula:

Structural formula of ethane can also be written as CH3CH3 or CH3 − CH3
If C = 3, then; CnH2n+2 = C3H2×3+2 = C3H8
Name of this compound is propane. It can be shown by following structural formula:

Structural formula of propane can also be written as CH3CH2CH3 or CH3 − CH2 − CH3

If C = 4, then; CnH2n+2 = C4H2×4+2 = C4H10

Name of this compound is butane. It can be shown by following structural formula:

Structural formula of propane can also be written as CH3CH2CH2CH3 or CH3 − CH2 − CH2 − CH3

If C = 5, then; CnH2n+2 = C5H2×5+2 = C5H12

Name of this compound is pentane. It can be shown by following structural formula:

Saturated Hydrocarbons (Alkane)
NameNo. of carbon atomsFormula
Methane1CH4
Ethane2C2H6
Propane3C3H8
Butane4C4H10
Pentane5C5H12
Hexane6C6H14
Heptane7C7H16
Octane8C8H18
Nonane9C9H20
Decane10C10H22

 

Unsaturated Hydrocarbons

Alkene: Hydrocarbons having at least one double bond between two carbon atoms are known as ALKENE. General formula of alkene is CnH2n; where n is number of carbon atoms.

If C = 1 then CnH2n = C1H2×1 = CH2

Name of this compound: Since, hydrocarbon having one carbon atom is known as Methane. Thus, Methane – ane + ene = Methene. But, alkene does not exist with one carbon atom, thus, methene does not exist.

If C = 2 then CnH2n = C2H2×2 = C2H4

Name of this compound is: ethane − ane + ene = ethene. This molecule can be shown by following structural formula.

If C = 3 then CnH2n = C3H2×3 = C3H6

Name of this compound is: butane − ane + ene = butene. This molecule can be shown by following structural formula.

Other alkenes are formed in similar way.

 

 

Alkyne

Hydrocarbons having at least one triple bond between two carbon atoms are known as alkyne. (Alkane – ane + yne = Alkyne). Similarly;

Ethane – ane + yne = Ethyne
Propane – ane + yne = Propyne
Butane – ane + yne = Butyne
Pentane – ane + yne = Pentyne

General formula of alkyne is CnH2n − 2. As in case of alkene, minimum two carbon atoms are required to form alkyne.

If C = 2, then; CnH2n − 2 = C2H2×2 − 2 = C2H2

The name of this compound is ethyne. This can be shown by following structural formula.

 

If C = 3, then; CnH2n − 2 = C3H2×3 − 2 = C3H4

The name of this compound is propyne. This can be shown by following structural formula.

If C = 4, then; CnH2n − 2 = C4H2×4 − 2 = C4H6

The name of this compound is butyne. This can be shown by following structural formula.

Other alkynes are formed in similar way.

 

Cyclic Hydrocarbon:

Carbon can form cyclic structure combining with carbon atoms. Such hydrocarbons are known as cyclic hydrocarbon. Structural formulae of some of the cyclic hydrocarbons are as follows:

Hydrocarbons: Nomenclature

Functional Group: Single atom or group of atoms, that have similar chemical properties are called functional group. For example: Halogen group, Carboxyl group, Aldehyde group, etc.

Alkyl group: −R is known as alkyl group.

Examples: −CH3 (Methyl) −C2H5 (Ethyl), −C3H7 (Propyl)

Halogen group: Halogen group is also known as halo group. −Cl (Chloro),−Br(Bromo),−I(Iodo) are halogen or halo group.

Alcohol: −OH is known as alcohol group.
Aldehyde: −CHO is known as aldehyde group. Its structural formula is as follows:

Ketone Group: −CO− is known as ketone group. This is also known as carbonic group. Its structural formula is as follows:

Carboxylic Acid Group: − COOH is known as carboxylic acid group; or simply as acid group. Its structural formula is as follows:

Nomenclature of Carbon Compounds:

International Union of Pure and Applied Chemistry (IUPAC) decided some rules to name the carbon compounds. This was done to maintain the uniformity throughout the world. Names which are given on this basis are popularly known as IUPAC name. The rules for nomenclature are as follows:

Identify the number of carbon atoms in carbon compound. Name the carbon compounds according to the number of carbon atoms.

Example: Saturated hydrocarbon having one carbon atom is named as Methane. Saturated hydrocarbon having two carbon atoms is named as Ethane.

Unsaturated hydrocarbon with double bond having two carbon atoms is named as Ethene.
Unsaturated hydrocarbon with triple bond between carbon atoms is named as Ethyne.

Functional groupPrefixSuffix
AlkylAlkyln/a
HalogenChloro− for chlorine,
Bromo− for bromine
Iodo− for iodine
n/a
Alcoholn/aol
Aldehyden/aal
Ketonen/aone
Carboxylic acidn/aoic acid
Double bondn/aene
Triple bondn/ayne

 

Nomenclature of Alkane:

Example: In this structure, there are four carbon atoms but no functional group is attached. Hence, its name is butane

Common name: Iso-butane.

IUPAC Name:

Number of carbon atoms in the longest chain = 3.
A methyl group is present at carbon number 2.
So, IUPAC Name is 2-methyl propane.

Example: Since there are five carbon atoms, hence its IUPAC name is pentane. Its common name is n-pentane.

Homologous Series:

Series of compounds with same general formula and functional group is known as homologous series. Compounds belonging to the same homologous series show similar properties. Compounds of homologous series differ by CH2 from their consecutive members. Each subsequent compound in a homologous series differs by 14 au. Example: Alkanes; such as, Methane, Ethane, Propane, Butane, etc. belong to same homologous series.

Properties of Compounds of Same Homologous Series

  1. Compounds of same homologous series have same general formula.
  2. Compounds of same homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, homologous series differ from their consecutive members by one carbon atom and two hydrogen atoms, i.e. by CH2
  3. Compounds of same homologous series have same chemical properties.
  4. Compounds of same homologous series differ by physical properties with increase or decrease in molecular mass.

 

 

Chemical Properties of Carbon Compounds

Combustion Reaction: Carbon and carbon compounds gives carbon dioxide, vapor, heat and light on burning in air. Following are some of the examples of combustion reaction of organic compounds:

C + O2  CO2 + Heat + Light

CH4 + 2O2  CO2 + 2H2O + Heat + Light

CH3C2OH + O2  CO2 + H2O + Heat + Light

Oxidation:

In combustion reaction, carbon compounds are oxidized in the presence of oxygen. The following example is different because alkaline KMnO4 is the oxidizing agent in this reaction.

CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) CH3COOH

Substitution Reaction:

Replacement of a functional group or any atom by another atom or functional group is known as substitution reaction. Substitution reactions are single displacement reactions.
When methane reacts with chlorine gas in the presence of sunlight, it gives chloromethane and hydrogen chloride.

CH4 + Cl2 + Sunlight CH3Cl + HCl

Some Important Organic Compounds

Ethanol (C2H5OH)

  • Ethanol is commonly known as alcohol and spirit.
  • General name of ethanol is ethyl alcohol.
  • Ethanol is the main constituent of all alcoholic drinks
  • Ethanol is soluble in water
  • Ethanol is a very good solvent
  • Ethanol is used in manufacturing of medicines, such as tincture iodine, cough syrup, etc.
  • Taking even small quantity of pure ethanol may prove lethal
  • Taking dilute ethyl alcohol can cause drunkenness

Reaction of ethanol with sodium metal:

When ethanol reacts with sodium, it gives sodium ethoxide and hydrogen gas.

2CH3CH2OH + 2Na 2CH3CH2ONa + H2

Oxidation of ethanol: Ethanol gives ethanoic acid on oxidation.

CH3CH2OH + (Alkaline KMnO4/Acidified K2Cr2O7) CH3COOH

Dehydration of ethanol: Ethanol gives ethene and water when it is heated with concentrated sulphuric acid.

CH3CH2OH + Conc. H2SO4  CH2=CH2 + H2O

Ethanoic Acid (CH3COOH)

Structural formula of ethanoic acid is as follows:

  • General name of ethanoic acid is acetic acid.
  • Melting point of ethanoic acid is 290K.
  • Ethanoic acid freezes in winter and hence it is also known as glacial acetic acid.
  • Ethanoic acid is a colorless liquid.
  • 5% to 8% solution of acetic acid in water is known as vinegar.
  • Vinegar is used as preservative in pickles.
  • Carboxylic acids are weak acid compared to mineral acids.

Reaction of ethanoic acid with base: Ethanoic acid gives sodium acetate when it reacts with sodium hydroxide.

CH3COOH + NaOH CH3COONa + H2O

Esterificaiton of ethanoic acid: Ethanoic acid gives ethyl acetate when it reacts with ethanol in presence of conc. sulphuric acid. This reaction is called esterification reaction.

CH3COOH + C2H5OH CH3COOC2H5 + H2O

Saponification: Ester of higher fatty acids gives sodium salt of higher fatty acid; when heated with glycerol and sodium hydroxide. Sodium salts of higher fatty acid are known as soaps. This reaction is called saponification (soap making).

Reaction of ethanoic acid with sodium carbonate and sodium bicarbonate:

Ethanoic acid gives sodium acetate, water and carbon dioxide when reacts with sodium carbonate or sodium bicarbonate (sodium hydrogen carbonate).

2CH3COOH + Na2CO3  2CH3COONa + CO2 + H2O

CH3COOH + NaHCO3  CH3COONa + CO2 + H2O

Soaps and Detergents:

Soap: Ester of higher fatty acids is called soap. It is manufactured by the reaction of easter of higher fatty acid with sodium hydroxide. The sodium salt so formed has cleansing property.

Detergent: Soap cannot form lather in hard water. To overcome this problem, detergents were introduced. Detergent is also known as soapless soap. Detergent is sodium salt of benzene sulphonic acid or sodium salt of long chain alkyl hydrogen sulphate.

Cleansing action of soap:

Soap molecule has two ends. One end is hydrophilic and another end is hydrophobic. In other words, one end is lipophobic (hydrophilic) and another end is lipophilic (hydrophobic). When soap is dissolved in water and clothes are put in the soapy solution, soap molecules converge in a typical fashion to make a structure; called micelle. The hydrophobic ends of different molecules surround a particle of grease and make the micelle; which is a spherical structure. In this, the hydrophilic end is outside the sphere and hydrophobic end is towards the centre of the sphere. That is how, soap molecules wash away dirt and grease by making micelles around them.

Soap and Hard Water: Hard water often contains salts of calcium and magnesium. Soap molecules react with the salts of calcium and magnesium and form a precipitate. This precipitate begins floating as an off-white layer over water. This layer is called scum. Soaps lose their cleansing property in hard water because of formation of scum. Detergents are used; instead of soaps; in hard water to overcome the problem. Detergents are usually ammonium or sulphonate salts of carboxylic acids. The charged ends of these compounds do not form precipitate with calcium or magnesium salts in hard water. Hence, detergents retain their cleansing property in hard water.

 

 


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