Carbon and Its Compounds Class 10 Science Notes – Complete Chapter

Carbon is a non-metallic element with atomic number 6. Its electronic configuration is 2, 4.

Carbon is found in a wide variety of compounds, both in living organisms and non-living materials.

Organic Chemistry: The branch of chemistry that deals with the study of carbon compounds, particularly hydrocarbons and their derivatives, is called organic chemistry.

Hydrocarbons: Compounds made up of carbon and hydrogen only are called hydrocarbons.

Examples:

• Methane – CH₄
• Ethane – C₂H₆
• Ethene – C₂H₄
• Ethyne – C₂H₂

The atomic number of carbon is 6, and its electronic configuration is 2, 4. Therefore, it has four electrons in its outermost shell.

To achieve a stable electronic configuration, carbon requires four more electrons.

However, carbon cannot easily gain or lose four electrons because:

• Gaining four electrons would produce a negatively charged ion with considerable electron-electron repulsion.
• Losing four electrons would require a very large amount of energy.

Therefore, carbon completes its outermost shell by sharing electrons with other atoms.

A chemical bond formed by the mutual sharing of electron pairs between two atoms is called a covalent bond.

Carbon forms covalent bonds with hydrogen, oxygen, nitrogen, sulphur, chlorine and other elements.

1. Single Covalent Bond

2. Double Covalent Bond

When two atoms share two pairs of electrons, a double covalent bond is formed.

Example: O=O and C₂H₄.

3. Triple Covalent Bond

When two atoms share three pairs of electrons, a triple covalent bond is formed.

Example: N≡N and C₂H₂.

Important: Carbon has a valency of four. Hence, it is called tetravalent.

Carbon can form:

1. Straight-chain compounds.
2. Branched-chain compounds.
3. Closed-chain or ring compounds.

The valency of carbon is four. Therefore, one carbon atom can form four covalent bonds with other carbon atoms or atoms of other elements.

Carbon forms compounds with hydrogen, oxygen, nitrogen, sulphur, chlorine and many other elements.

Remember: Catenation and tetravalency are the two major reasons behind the large number of carbon compounds.

Hydrocarbons are compounds containing only carbon and hydrogen.

They are classified into two main types:

• Saturated hydrocarbons
• Unsaturated hydrocarbons

Hydrocarbons in which carbon atoms are connected by only single covalent bonds are called saturated hydrocarbons.

They are known as alkanes.

General formula:

CₙH₂ₙ₊₂

Examples:

Hydrocarbons containing at least one carbon-carbon double bond or triple bond are called unsaturated hydrocarbons.

They are of two types.

1. Alkenes

Hydrocarbons containing at least one carbon-carbon double bond are called alkenes.

General formula: CₙH₂ₙ

Example:

• Ethene – C₂H₄
• Propene – C₃H₆

2. Alkynes

Hydrocarbons containing at least one carbon-carbon triple bond are called alkynes.

General formula: CₙH₂ₙ₋₂

Example:

• Ethyne – C₂H₂
• Propyne – C₃H₄

Hydrocarbons in which carbon atoms are arranged in the form of a ring are called cyclic hydrocarbons.

Examples:

• Cyclohexane – C₆H₁₂ (saturated cyclic hydrocarbon).
• Benzene – C₆H₆ (unsaturated cyclic hydrocarbon).

A functional group is an atom or group of atoms present in an organic compound that determines its characteristic chemical properties.

Organic compounds can be formed by replacing one or more hydrogen atoms of a hydrocarbon with other atoms or groups of atoms.

Nomenclature is the systematic process of naming chemical compounds.

The International Union of Pure and Applied Chemistry (IUPAC) provides a uniform system for naming organic compounds.

The process of burning a carbon compound in air or oxygen to produce carbon dioxide, water, heat and light is called combustion (in complete combustion).

Combustion reactions are exothermic reactions because they release heat.

Example – Combustion of methane:

CH₄ + 2O₂ → CO₂ + 2H₂O + Heat + Light

Combustion of ethane:

2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O + Heat + Light

Important points:

• Saturated hydrocarbons generally burn with a clean blue flame when sufficient oxygen is available.
• Unsaturated hydrocarbons generally burn with a yellow, sooty flame in air.
• Incomplete combustion can produce carbon monoxide and soot.

The addition of oxygen or removal of hydrogen from a substance is called oxidation.

Alcohols can be oxidised to carboxylic acids.

For example, ethanol is oxidised to ethanoic acid using alkaline potassium permanganate (KMnO₄) or acidified potassium dichromate (K₂Cr₂O₇).

CH₃CH₂OH + 2[O] → CH₃COOH + H₂O

Oxidising agents:

• Alkaline KMnO₄
• Acidified K₂Cr₂O₇

The reaction in which atoms are added to an unsaturated compound is called an addition reaction.

Hydrogenation is the addition of hydrogen to an unsaturated hydrocarbon in the presence of a catalyst such as nickel, palladium or platinum.

Example:

CH₂=CH₂ + H₂ → CH₃–CH₃

(Catalyst: Nickel; heat)

The reaction in which one or more hydrogen atoms of a hydrocarbon are replaced by atoms of other elements is called a substitution reaction.

Substitution reactions are characteristic of saturated hydrocarbons.

Example:

CH₄ + Cl₂ → CH₃Cl + HCl

Condition: Sunlight.

In this reaction, one hydrogen atom of methane is replaced by a chlorine atom.

Physical Properties:

• It is a colourless liquid.
• It is soluble in water.
• It is neutral to litmus.
• It is inflammable.

1. Reaction with Sodium

Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas.

2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

2. Dehydration of Ethanol

When ethanol is heated with excess concentrated sulphuric acid at 170°C, it loses water and forms ethene.

C₂H₅OH → CH₂=CH₂ + H₂O

Condition: Concentrated H₂SO₄, 170°C.

Ethanoic acid is commonly known as acetic acid.

A 5–8% solution of ethanoic acid in water is called vinegar.

Pure ethanoic acid freezes at approximately 16.6°C. It is therefore also known as glacial acetic acid.

Physical Properties:

• It is a colourless liquid.
• It has a pungent smell.
• It is soluble in water.
• It turns blue litmus red.

1. Esterification Reaction

When ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid, an ester is formed.

CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O

The ester formed is ethyl ethanoate. Esters generally have a pleasant, fruity smell and are used in perfumes and flavouring agents.

2. Reaction with a Base

Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.

CH₃COOH + NaOH → CH₃COONa + H₂O

3. Reaction with Sodium Carbonate

Ethanoic acid reacts with sodium carbonate to produce sodium ethanoate, water and carbon dioxide.

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

4. Reaction with Sodium Hydrogen Carbonate

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

Soaps are sodium or potassium salts of long-chain carboxylic acids.

A soap molecule has two distinct parts:

1. Hydrophobic end: The long hydrocarbon chain that is insoluble in water but soluble in oil and grease.
2. Hydrophilic end: The ionic carboxylate end that is attracted to water.

Soap removes dirt and grease through the formation of structures called micelles.

The cleansing process takes place as follows:

1. The hydrophobic end of the soap molecule attaches itself to oily dirt.
2. The hydrophilic end remains attracted towards water.
3. Many soap molecules surround the dirt particle.
4. A spherical structure called a micelle is formed.
5. The dirt gets suspended in water and can be washed away.

Micelle: A spherical aggregate of soap molecules formed in water, with the hydrocarbon ends directed towards the oily dirt and the ionic ends towards water.

Why are detergents preferred in hard water?

Hard water contains calcium and magnesium ions. These ions react with soap to form insoluble substances called scum. This reduces the cleansing efficiency of soap.

Detergents generally do not form such insoluble precipitates and therefore work effectively in hard water.

1. Covalent Bond: A chemical bond formed by the mutual sharing of electron pairs between atoms.

2. Catenation: The property of carbon atoms to form bonds with one another, producing long chains, branched chains and rings.

3. Tetravalency: The property of carbon by which it forms four covalent bonds.

4. Hydrocarbons: Compounds containing only carbon and hydrogen.

5. Saturated Hydrocarbons: Hydrocarbons containing only single bonds between carbon atoms.

6. Unsaturated Hydrocarbons: Hydrocarbons containing one or more double or triple bonds between carbon atoms.

7. Functional Group: An atom or group of atoms that determines the characteristic chemical properties of an organic compound.

8. Homologous Series: A family of organic compounds having the same functional group and similar chemical properties, with successive members differing by –CH₂–.

9. Oxidation: A chemical process involving the addition of oxygen or removal of hydrogen.

10. Hydrogenation: The addition of hydrogen to an unsaturated compound in the presence of a catalyst.

11. Esterification: The reaction between an alcohol and a carboxylic acid to form an ester and water.

12. Saponification: The alkaline hydrolysis of an ester to form an alcohol and the salt of a carboxylic acid.

13. Micelle: A spherical aggregate of soap molecules formed in water.

Q1. Why does carbon form covalent bonds?

Carbon has four valence electrons. It cannot easily gain or lose four electrons, so it shares electrons with other atoms to achieve a stable electronic configuration.

Q2. What are the two important properties responsible for the versatility of carbon?

Catenation and tetravalency.

Q3. Why is diamond hard but graphite soft?

In diamond, each carbon atom is bonded to four other carbon atoms in a rigid three-dimensional structure. In graphite, carbon atoms form layers that can slide over one another.

Q4. Why does graphite conduct electricity but diamond does not?

Graphite contains free electrons that can move and conduct electricity. Diamond does not have free electrons.

Q5. What is the difference between alkanes and alkenes?

Alkanes contain only single carbon-carbon bonds, whereas alkenes contain at least one carbon-carbon double bond.

Q6. What happens when ethanol reacts with sodium?

Ethanol reacts with sodium to produce sodium ethoxide and hydrogen gas.

Q7. What is vinegar?

Vinegar is a dilute aqueous solution of ethanoic acid, generally containing about 5–8% ethanoic acid.

Q8. Why are soaps ineffective in hard water?

Soaps react with calcium and magnesium ions in hard water to form insoluble scum, reducing their cleansing efficiency.

Q9. What is the function of concentrated sulphuric acid in the dehydration of ethanol?

It acts as a dehydrating agent and removes water from ethanol to form ethene.

Q10. What is the importance of hydrogenation?

Hydrogenation is used in industries to convert unsaturated vegetable oils into more saturated fats, such as vanaspati ghee.

1. The valency of carbon is:

(a) 1
(b) 2
(c) 3
(d) 4

2. Which of the following is an allotrope of carbon?

(a) Sulphur
(b) Graphite
(c) Oxygen
(d) Nitrogen

3. The general formula of alkanes is:

(a) CₙH₂ₙ
(b) CₙH₂ₙ₊₂
(c) CₙH₂ₙ₋₂
(d) CₙHₙ

4. Which functional group is present in alcohols?

(a) –COOH
(b) –CHO
(c) –OH
(d) –CO–

5. The molecular formula of buckminsterfullerene is:

(a) C₆₀
(b) C₆H₆
(c) C₂H₆
(d) C₆H₁₂

6. Which gas is released when ethanoic acid reacts with sodium hydrogen carbonate?

(a) Hydrogen
(b) Oxygen
(c) Carbon dioxide
(d) Nitrogen

7. Which of the following is used as an oxidising agent?

(a) NaCl
(b) KMnO₄
(c) NaOH
(d) HCl

8. The process of converting vegetable oil into vanaspati ghee is called:

(a) Oxidation
(b) Substitution
(c) Hydrogenation
(d) Esterification