NCERT Class 10 Science Chapter 4 Notes Carbon and its Compounds- Download PDF Notes

NCERT Notes for Class 10 Chapter 4: Download PDF

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NCERT Notes for Class 10 Chapter 4

These notes give you a basic idea of the key features of carbon and its compounds. Some of the main topics covered in Science Class 10 Chapter 4 notes PDF are: definitions, bonding in carbon—the covalent bond, versatile nature of carbon, saturated and unsaturated carbon compounds, homologous series, the nomenclature of carbon compounds, chemical properties of carbon compounds, some important carbon compounds—ethanol and ethanoic acid, soaps, and detergents. Students must go through each topic in the carbon and its compounds, which are given below.

Bonding in Carbon: The Covalent Bond

• We know that an ionic bond is formed when an atom loses an electron and another atom gains an electron.
• In the case of carbon, which has 4 electrons in its outermost shell, it is not feasible to lose all of the 4 electrons due to high energy requirements or even gain 4 electrons due to repulsion between the electrons.
• Therefore, carbon forms bonds by sharing its 4 electrons with another carbon atom, hence completing its octet. This type of bond is called a covalent bond.
• This type of bond is also formed between other compounds, such as in H₂, O₂, N₂, etc.

Allotropes of Carbon

Diamond: In a diamond, every carbon atom is bonded to another four carbon atoms, giving rise to a rigid three-dimensional structure.

Graphite: In graphite, every carbon atom is bonded to three other carbon atoms in the same plane, giving rise to a hexagonal array.

C-60 Buckminsterfullerene: In C-60 Buckminsterfullerene, carbon atoms are arranged in the shape of a football.

Versatility Nature of Carbon

1. Carbon has the property of catenation, that is, it has the ability to bond with carbon atoms, giving rise to a large molecule.

Carbon can bond with a single bond, a double bond, or a triple bond.

2. Carbon forms strong bonds with elements, and because of its small size, the nucleus is able to hold upon the shared pair of electrons. Carbon forms bond with many elements, such as oxygen, hydrogen, nitrogen, sulphur, chlorine, etc, thus forming compounds with specific properties.

Saturated and Unsaturated Carbon Compounds

Saturated Carbon Compounds

Carbon compounds which involve single bonds are called saturated carbon compounds.

Unsaturated Carbon Compounds

Carbon compounds which involve double or triple bonds are called unsaturated carbon compounds.

Naming of Saturated Carbon Compounds based on the number of Carbon atoms

The functional group in Carbon Compounds

Chains, Branches and Rings

Carbon Chains: Carbon atoms can form long chains by bonding with other carbon atoms. These can be straight or branched chains.

Example: Straight chain: Butane (C₄H₁₀) → CH₃–CH₂–CH₂–CH₃

Branched Chains: Chains where one or more carbon atoms branch off from the main chain.

Example: Isobutane → CH₃–CH(CH₃)–CH₃

Ring Compounds (Cyclic Compounds): Carbon atoms can also form closed rings. These can be saturated (single bonds) or unsaturated (double or triple bonds).

Example: Cyclohexane (C₆H₁₂), Benzene (C₆H₆)

Homologous Series

A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.

Examples:

Alkanes: CH₄, C₂H₆, C₃H₈, ......

Alcohols: CH₃OH, C₂H₅OH, C₃H₇OH...

Nomenclature of Carbon Compounds

1. Find the number of carbon atoms in the compound, and based on the number of carbon atoms, name the compound as given above. For example, a compound with 4 carbon atoms would have the name butane.

2. If a functional group is present, the name of the compound is given based on the functional group with either a prefix or a suffix.

3. If the name of the functional group is to be given as a suffix, and if the suffix of the functional group starts with a vowel a, e, i, o, u, then the name of the carbon chain is modified by replacing the final ‘e’ with the appropriate suffix. For example, a 4-carbon chain with a ketone group would be named Butane – ‘e’ = Butan + ‘one’ = Butanone.

Chemical Properties of Carbon Compounds

Combustion

Carbon reacts with oxygen, giving out carbon dioxide, heat and light.

$\begin{aligned} & \mathrm{C}+\mathrm{O}_2 \rightarrow \mathrm{CO}_ 2+\text { heat and light } \\ & \mathrm{CH}_4+\mathrm{O}_2 \rightarrow \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}+\text { heat and light } \\ & \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH}+\mathrm{O}_2 \rightarrow \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O}+\text { heat and light }\end{aligned}$

Why do substances burn with a flame?

Substances burn with a flame because a flame is produced when gaseous substances burn and glow. For instance, on ignition of wood or charcoal, the volatile substances present in them vapourise and burn with a flame. Each element produces its own characteristic colour.

Formation of coal and petroleum

Coal has been formed from remains of trees and plants which have been subjected to various biological and geological processes for millions of years ago, wherein they were crushed and buried down the earth layer by layer by earthquake or volcanoes.

Petroleum has been formed from remains of plants and animals in the sea which have been attacked by bacteria under high pressures and converted into oil and gas, which are trapped between the rocks.

Oxidation

When oxygen is added to the compound, the reaction is called oxidation reaction. It is done in the presence of an oxidising agent.

$\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH} \xrightarrow[\text { OrAcidified }_2 \mathrm{Cr}_2 \mathrm{O}_7]{\text { AlkalinKMn }_4+\mathrm{Heat}} \mathrm{CH}_3 \mathrm{COOH}$

Addition Reaction

When hydrogen is added to an unsaturated compound in the presence of a catalyst such as palladium or nickel, giving rise to saturated hydrocarbons, the reaction is called an addition reaction.

Substitution Reaction

When an atom or group of atoms are replaced by another atom, the reaction is called substitution reaction.

Some Important Carbon Compounds - Ethanol And Ethanoic Acid

Ethanol

Ethanol is commonly called alcohol, it is a good solvent which is soluble in water also and is used as medicine to treat cough.

Reactions of Ethanol:

(Reaction with sodium)

$2Na + 2CH_{3}CH_{2}OH\rightarrow 2CH_{3}CH_{2}O-Na^{+} +H_{2}$

(Reaction to give unsaturated hydrocarbon)

$\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH} \xrightarrow[Heat]{Conc.\mathrm{H}_2\mathrm{SO}_4} \mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}_2 \mathrm{O}$

Denatured Alcohol: To prevent the misuse or wrong use of ethanol produced for industrial use, it is made unfit for use that is for drinking by adding poisonous substances like methanol to it and also dyes to give it a fake colour. This alcohol is called denatured alcohol.

Ethanoic Acid

Ethanoic Acid is colloquially called acetic acid, its 5-8% solution is called vinegar and is used widely for cooking purposes. Pure ethanoic acid is called glacial acetic acid.

Reactions of ethanoic acid:

(Esterification reaction)

$\mathrm{CH}_3 \mathrm{COOH}+\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH} \rightarrow \mathrm{CH}_3 \mathrm{COOCH}_2 \mathrm{CH}_3+\mathrm{H}_2 \mathrm{O}$

(Reaction with a base)

$\mathrm{NaOH}+\mathrm{CH}_3 \mathrm{COOH} \rightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}$

(Reaction with carbonates and hydrogen carbonates)

$\begin{aligned} & 2 \mathrm{CH}_3 \mathrm{COOH}+\mathrm{Na}_2 \mathrm{CO}_3 \rightarrow 2 \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2 \\ & \mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaHCO}_3 \rightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\end{aligned}$

Soaps and Detergents

Soaps are the long-chain carboxylic acids of sodium or potassium. The ionic-end of soap called head interacts with water and the carbon chain called tail interacts with oil.

In hard water, soaps form scum with water. Hence, detergents are used to overcome this problem, as detergents are sodium salts of sulfonic acids or ammonium salts with chlorides or bromide ions. Their charged ends do not form scum and thus are used for cleansing purposes.

Carbon and Its Compounds: Previous Years' Questions and Answers

Some important previous years' questions are given below:

Question 1. $CH_{3}-CH_2-OH\xrightarrow[Heat]{Alkaline KMnO_{4}}CH_{3}-COOH$

In the above given reaction alkaline $KMnO_4$ acts as
(a) reducing agent
(b) oxidizing agent
(c) catalyst
(d) dehydrating agent

Answer:

Here, ethanol is converted to ethanoic acid.
$KMnO_4$ acts as an oxidising agent as it removes hydrogen from $CH_3CH_2OH$ and adds one oxygen to it.

Hence, the correct answer is option (b).

Question 2. Chlorine reacts with saturated hydrocarbons at room temperature in the
(a) absence of sunlight
(b) presence of sunlight
(c) presence of water
(d) presence of hydrochloric acid

Answer:
Chlorine reacts with saturated hydrocarbon at room temperature in the presence of sunlight,
$CH_{4}+Cl_{2}\overset{sunlight}{\rightarrow}CH_{3}Cl+HCl$
$CH_3Cl+Cl_{2}\overset{sunlight}{\rightarrow}CH_{2}Cl_{2}+HCl$
$CH_2Cl_{2}+Cl_{2}\overset{sunlight}{\rightarrow}CHCl_{3}+HCl$
$CHCl_{3}+Cl_{2}\overset{sunlight}{\rightarrow}CCl_{4}+HCl$
Hence, the correct answer is option (b).

Question 3. Which member of the homologous series of alkynes corresponds to C₃H₄?
a) C₆H₆ 

b) C₂H_₄ 

c) C₂H₆ 

d) C₃H₄

Answer:

The general formula of alkynes is C_nH_2n-2.

When n = 3, it gives C₃H₄.

Hence, the correct answer is option (d).

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