CLASS 10 SCIENCE NOTES Chapter 4: Carbon and Its Compounds

Carbon is a versatile non-metal (atomic number 6; symbol C). It is present in the earth’s crust (0.02% as minerals) and the atmosphere (0.03% as carbon dioxide).

Importance of Carbon All living things (plants, animals, human bodies) are carbon based. Carbon compounds are mostly found in food, clothing, medications, and books.

Properties of Carbon:

Carbon is special. Carbon does not want to lose 4 electrons , or gain 4 electrons easily . Carbon shares electrons.

Tetravalency:

Carbon has 4 valence electrons. To achieve noble gas configuration, it forms 4 bonds with other atoms.

Catenation: The wonderful capacity of carbon atoms to join with other carbon atoms to form long chains, branches and rings.

Covalent Bonding: The type of chemical bond formed by the mutual sharing of electron pairs between atoms.

NCERT Complete Notes

1. Bonding in Carbon

Electronic Configuration of Carbon: Carbon has an atomic number of six. Its electronic configuration is K=2, L=4. It needs 4 more electrons to complete its octet.

Why carbon forms covalent bonds:

It cannot gain four electrons to form the C anion because a nucleus with six protons would struggle to hold ten electrons.
It cannot lose four electrons to form a C cation because doing so would require a massive amount of energy and result in a highly unstable nucleus.
Carbon overcomes this by sharing valence electrons.

Formation of Molecules (Covalent Bonds):

Hydrogen Molecule (H₂):
Hydrogen has one electron. Two hydrogen atoms share one electron each to form a single covalent bond (H-H).
Oxygen Molecule (O₂):
Oxygen contains 6 valence electrons. A double bond (O=O) is formed when two O atoms share two electron pairs.
Nitrogen Molecule (N₂):
There are five valence electrons in nitrogen. A triple bond (N≡N) is formed when two N atoms share three pairs of electrons.
Methane (CH₄): Four single bonds are formed when one carbon atom shares its four valence electrons with four hydrogen atoms.

[Add Image Here: Neat labeled diagrams for H2, O₂, N₂, and CH₄ electron dot structures]

2. Versatile Nature of Carbon

Tetravalency

Definition:

Tetra stands for four, and valency is the ability to combine. Tetravalency (carbon) The property of having a valency of four.

Explanation:

Carbon can make four bonds with other atoms or atoms of some other mono-valent element like hydrogen, chlorine, etc.

Examples: Methane (CH₄), Carbon tetrachloride (CCl₄)

Catenation

Definition:

The ability of a carbon atom to form covalent bonds with other carbon atoms to create long straight chains, branched chains, or closed rings.

Explanation: The carbon-carbon bond is very strong and stable, so there can be infinite carbon compounds.

Importance:

That is why organic chemistry is so big. It produces millions of different carbon compounds .

3. Hydrocarbons

Molecules with only carbon and hydrogen are known as hydrocarbons.

Saturated Hydrocarbons (Alkanes)

Definition: Hydrocarbons in which all the carbon atoms are joined by single covalent bonds only.
Examples: Methane (CH₄) and Ethane (C₂H₆).
General Formula: CnH₂n+₂

Unsaturated Hydrocarbons

Alkenes: Alkenes are hydrocarbons that have two carbon-to-carbon bonds. General formula: CnH₂n. For example, consider ethane (C₂H₄).
Alkynes: Hydrocarbons that have one or more carbon-carbon triple bonds. General formula: CnH₂n-₂. Example: ethyne (C₂H₂).

Comparison Table

Saturated Hydrocarbons	Unsaturated Hydrocarbons
Contain only single bonds between carbon atoms.	Contain double or triple bonds between carbon atoms.
Generally less reactive.	Highly reactive.
Burn with a clean blue flame.	Burn with a yellow, sooty flame.
Example: Alkanes	Example: Alkenes and Alkynes

4. Functional Groups

Atoms or groups of atoms which replace hydrogen in a hydrocarbon chain and which determine the chemical properties of the compound.

Functional Group	Formula/Structure	Suffix/Prefix	Example
Alcohol	-OH	-ol	Ethanol (CH₃CH₂OH)
Aldehyde	-CHO	-al	Ethanal (CH₃CHO)
Ketone	>C=O (Middle of chain)	-one	Propanone (CH₃COCH₃)
Carboxylic Acid	-COOH	-oic acid	Ethanoic acid (CH₃COOH)
Halo Group	-Cl, -Br, -I	Chloro-, Bromo-	Chloromethane (CH₃Cl)

5. Nomenclature of Carbon Compounds (IUPAC Naming)

Naming Rules:

Count the number of carbon atoms, and that gives you the root name (1=Meth, 2=Eth, 3=Prop, 4=But, 5=Pent).
Determine whether the bonds (-ane, -ene, -yne) are single, double, or triple.
After determining the functional group, add the proper prefix or suffix.

Examples:

Methane: 1 Carbon, single bonds = CH₄
Ethane: 2 Carbons, single bonds = C₂H₆
Propane: 3 Carbons, single bonds = C₃H₈
Butane: 4 Carbons, single bonds = C₄H₁₀
Pentane: 5 Carbons, single bonds = C₅H₁₂

6. Chemical Properties of Carbon Compounds Combustion

Definition: Burning of carbon compounds in the presence of oxygen to give CO₂, water, heat, and light.

Equation: [CH₄ + 2O₂ = CO₂ + 2H₂O + Heat + Light]

Oxidation

Definition: Addition of oxygen to a compound. Alcohols can be converted to carboxylic acids using oxidising agents like alkaline KMnO₄..

Equation: CH₃CH₂OH + [O] (Alkaline KMnO₄ + Heat) → CH₃COOH + H₂O

Addition Reaction

Definition: Unsaturated hydrocarbons add hydrogen in the presence of catalysts (like palladium or nickel) to give saturated hydrocarbons. This is used in the hydrogenation of vegetable oils.

Equation: C₂H₄ + H₂ (Ni catalyst) → C₂H₆

Substitution Reaction

Definition: A reaction in which an atom or group of atoms replaces another. In sunlight, halogens replace saturated hydrocarbons.

Equation: [CH₄ + Cl₂ (Sunlight) → CH₃Cl + HCl]

7. Ethanol (Ethyl Alcohol)

Structure: CH₃-CH₂-OH
Properties: Liquid at room temperature, soluble in water in all proportions, good solvent.
Uses: Used in medicines (tincture iodine, cough syrups), alcoholic beverages, antifreeze in automobiles.
Important Reactions: Reaction with Sodium: 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa (Sodium ethoxide) + H₂ Dehydration: CH₃CH₂OH (Hot conc. H₂SO₄) → CH₂=CH₂ + H₂O

8. Ethanoic Acid (Acetic Acid)

Structure: CH₃-COOH
Properties: colourless liquid, sour taste. Pure ethanoic acid freezes in winter, hence called glacial acetic acid.
Vinegar: A 5-8% solution of ethanoic acid in water is called vinegar, used as a preservative in pickles.
Reactions: Esterification: CH₃COOH + CH₃CH₂OH (Acid catalyst) → CH₃COOCH₂CH₃ (Ester) + H₂OReaction with base: CH₃COOH + NaOH → CH₃COONa + H₂O

9. Soaps and Detergents

Soap Molecule Structure: A soap molecule has two parts: a hydrophilic (water-loving) ionic head (COO⁻Na⁺) and a hydrophobic (water-hating) long hydrocarbon tail.

Micelle Formation & Cleansing Action: Dirt is mostly oily. The hydrophobic tail attaches to the oil/dirt, while the hydrophilic head points outwards towards water. This forms a spherical structure called a micelle. When agitated, the dirt gets pulled into the water, cleaning the fabric.

Hard Water & Detergents: Hard water contains Calcium and magnesium salts. Soaps react with these to form an insoluble substance called ‘scum’, making them ineffective. Detergents are sodium salts of sulphonic acids; they do not form scum in hard water and clean effectively.

[Add Image Here: Neat labeled diagram of Soap Micelle Formation showing Hydrophilic head and Hydrophobic tail]

NCERT Back Exercise & CBSE Important Questions

Q1 Why does carbon form covalent compounds? (1 Mark):

Answer: Carbon has 4 valence electrons. It cannot easily lose or gain 4 electrons due to energy constraints. Hence, it shares electrons to achieve a stable noble gas configuration, forming covalent bonds.

Q2: What do structural isomers mean? Provide an illustration. (2 Points):

Answer; Structural isomers are compounds with the same molecular formula but different structural configurations. Example: Butane (C₄H₁₀) has two isomers: n-butane (straight chain) and isobutane (branched chain).

Q3: Differentiate between soap and detergent. Why is detergent better for hard water? (2 Marks):

Answer:
1. Soap is the sodium/potassium salt of long-chain carboxylic acid, whereas detergent is the sodium salt of long-chain sulphonic acid.
2. While some detergents are not biodegradable, soap is.
3. Soaps will produce scum in hard water, whereas detergents will not. Detergents work better with hard water because their calcium and magnesium salts dissolve in water, preventing scum formation.

Q4 : Write notes on esterification and saponification with chemical equations.(5 Marks)

Ans:
Esterification: The reaction between an alcohol and a carboxylic acid in the presence of a concentrated acid catalyst to produce a sweet-smelling substance called an ester.
Eq.: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O
Saponification: The alkaline hydrolysis of esters to produce soap and alcohol.
Eq: CH₃COOC₂H₅ + NaOH → CH₃COONa (Soap) + C₂H₅OH

Assertion and Reason:

Assertion (A): One saturated hydrocarbon is methane.
Reason (R): Single covalent bonds with hydrogen satisfy all four of carbon’s valencies in methane.
Answer: A and R are both true and R is the correct explanation of A.

Case-Based/Competency Question:

Case: A compound X is a major constituent of wine and beer. Upon heating with alkaline KMnO₄, it transforms into compound Y. Compound Y turns blue litmus red.
Q. Write the reaction and identify X and Y.
Answer: X is ethanol (C2H50H) which is used in alcoholic drinks. Y is ethanoic acid (CH3COOH) which is an acid.
Reaction: C_2H_5OH + [O] -> CH_3COOH + H_2O

Quick Revision Notes (One-Page Sheet)

Carbon allotropes: diamond (hardest, insulator) graphite (soft, good conductor) fullerene (C-60, buckyball form)
Catenation: self-connection of carbon atoms.
Homologous Series: a group of compounds that share the same functional group but differ in mass by 14 u or a -CH2 unit.
Important Formulae:
Alkane (CnH₂n+2).
Alkenes (CnH₂n)
Alkyne (CnH₂n-₂)
Ethanol (C₂H₅OH).
Ethanoic acid (CH₃COOH).
Hydrogenation is the conversion of unsaturated vegetable oils to saturated fats using a nickel catalyst.
Scum: An insoluble precipitate formed when soap reacts with calcium and magnesium ions in hard water.

Most Important Diagrams (To Practice)

Make sure you draw and label these for your board exams:

Methane Structure: Tetrahedron geometry or dot structure.
Ethane Structure: Showing C-C single bonds and C-H bonds.
Ethene Structure: Showing the C=C double bond.
Ethyne Structure: Showing C≡C triple bond.
Covalent Bond Formation: Circles showing electron sharing in O₂ and N₂.
Soap Micelle Structure: Radial arrangement of hydrophobic tails inward.
Functional Groups Chart: Neat table showing structural formulas.

[Webmaster: Insert all above-drawn diagrams here in high-resolution JPG/PNG format]

Exam Tips & Frequently Asked CBSE Topics

Don’t miss these topics, as these are seen almost every year in CBSE Class 10 Science Exams:

Tetravalency & Catenation: Learn why carbon has millions of compounds.
Covalent Bonding: Practise drawing electron dot structures (very high chance for 2 mark questions).
Functional Groups: Identify functional groups from given chemical structures.
Ethanol vs Ethanoic Acid: Memorize physical and chemical difference tables.
Soap and Detergent: Cleansing action of soap and the hard water disadvantage.
Chemical Reactions: Specifically Oxidation, Addition, and Substitution.

Chapter Summary for Last-Minute Revision

1. With valency 4 and atomic number 6, carbon is a non-metal.
2. In order to achieve the noble gas configuration, carbon shares electrons to form covalent bonds.
3. Carbon’s special capacity to form lengthy chains is known as catenation.
4. Carbon can form bonds with four other atoms due to tetravalency.
5. Hydrocarbons consist solely of carbon and hydrogen.
6. Single bonds are present in saturated hydrocarbons, or alkanes.
7. Double (Alkenes) or triple (Alkynes) bonds are found in unsaturated hydrocarbons.
8. A homologous series differs by -CH2 between adjacent members while sharing the same functional group.
9. The chemical characteristics of organic compounds (alcohol, aldehyde, ketone, and carboxylic acid) are determined by their functional groups.
10. Carbon dioxide, water, heat, and light are produced when carbon compounds burn.
11. Carboxylic acids are created when alcohols oxidise.
12. Addition reactions (hydrogenation) occur in unsaturated compounds.
13. Saturated compounds react with halogens through substitution.
14. Ethanol is an effective solvent and the active component of alcoholic beverages.
15. When ethanol and ethanoic acid react, esterification results.
16. The head and tail of soap molecules are hydrophilic and hydrophobic, respectively.
17. When soap traps dirt or oil in the middle of its structure, micelles are created.
18. Soap turns into insoluble scum when exposed to hard water.
19. Detergents function well in hard water and do not produce scum.
20. Keep in mind the Topper Rule: You will receive a perfect score if you fully comprehend the material and practise drawing electron dot structures.

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