Class 10 Science Chapter 4 Carbon and Its Compounds Notes
🔹 1. Bonding in Carbon
Why Carbon Forms Covalent Bonds?
Atomic number of carbon = 6
Electronic configuration = 2, 4
Carbon needs 4 electrons to complete octet
Cannot:
Gain 4 electrons → C⁴⁻ unstable
Lose 4 electrons → C⁴⁺ requires high energy
Hence, carbon shares electrons → forms covalent bonds
Covalent Bond
A covalent bond is formed by mutual sharing of electron pairs between two atoms so that each attains a stable noble gas configuration.
Types of Covalent Bonds
Single bond (—): 1 pair shared (H₂, Cl₂)
Double bond (=): 2 pairs shared (O₂, CO₂)
Triple bond (≡): 3 pairs shared (N₂)
🔹 2. Electron Dot Structure
Electron dot structure shows:
Valence electrons
Shared electron pairs
Octet rule
Examples:
H₂
CH₄
CO₂
H₂S
🔹 3. Physical Properties of Organic Compounds
Low melting and boiling points
Weak intermolecular forces
Poor conductors of electricity
Mostly covalent in nature
🔹 4. Allotropes of Carbon
Allotropy
The existence of an element in different physical forms but with same chemical properties.
Main Allotropes of Carbon
(i) Diamond
Each carbon bonded to 4 carbons
Hardest substance
Electrical insulator
Used in cutting, drilling, jewellery
(ii) Graphite
Each carbon bonded to 3 carbons
Good conductor of electricity
Used as lubricant, pencil lead
(iii) Fullerene (C₆₀)
Spherical structure (football-like)
Dark solid
🔹 5. Versatile Nature of Carbon
Carbon forms a large number of compounds due to:
(i) Catenation
Self-linking of carbon atoms to form:
Straight chains
Branched chains
Ring structures
(ii) Tetravalency
Carbon has valency 4, so forms four covalent bonds.
🔹 6. Hydrocarbons
Compounds containing only carbon and hydrogen.
Types of Hydrocarbons
(a) Saturated Hydrocarbons (Alkanes)
General formula: CnH₂n+2
Single bonds only
Example: CH₄, C₂H₆
(b) Unsaturated Hydrocarbons
Alkenes: CnH₂n (double bond)
Alkynes: CnH₂n−2 (triple bond)
🔹 7. Isomerism
Compounds having:
Same molecular formula
Different structural formula
Different properties
Example: Butane (C₄H₁₀)
🔹 8. Homologous Series
A series of organic compounds:
Same functional group
Similar chemical properties
Successive members differ by –CH₂ (14 u)
Characteristics
Same general formula
Gradual change in physical properties
🔹 9. Functional Group
An atom or group of atoms that:
Determines chemical properties of a compound
Examples:
–OH → Alcohol
–COOH → Carboxylic acid
–CHO → Aldehyde
🔹 10. Nomenclature of Organic Compounds (IUPAC)
Steps:
Identify longest carbon chain
Identify functional group
Use:
Word Roots
| No. of C | Root |
|---|---|
| 1 | Meth |
| 2 | Eth |
| 3 | Prop |
| 4 | But |
| 5 | Pent |
🔹 11. Chemical Properties of Carbon Compounds
(i) Combustion
Saturated → clean blue flame
Unsaturated → sooty flame
(ii) Oxidation
Alcohol → Acid
Using oxidising agents:
KMnO₄
K₂Cr₂O₇
(iii) Addition Reaction
Hydrogenation of unsaturated compounds:
Uses Ni / Pt / Pd catalyst
Vegetable oil → vegetable ghee
(iv) Substitution Reaction
Replacement of H atom by another atom/group.
🔹 12. Ethanol (C₂H₅OH)
Physical Properties
Colourless liquid
Soluble in water
Neutral to litmus
Chemical Properties
Burns with blue flame
Reacts with Na → H₂ gas
Dehydration → Ethene
🔹 13. Ethanoic Acid (CH₃COOH)
Common name: Acetic acid
5–8% solution → Vinegar
Turns blue litmus red
Reactions
Esterification
With bases → salt + water
With carbonates → CO₂
🔹 14. Soaps and Detergents
Soap
Sodium / potassium salts of fatty acids
Biodegradable
Ineffective in hard water
Detergent
Sulphonate salts
Effective in hard water
Non-biodegradable
Cleansing Action
Soap/detergent forms micelles
Hydrophobic tail + hydrophilic head
Dirt removed with water
Scum
Formed when soap reacts with Ca²⁺ / Mg²⁺ in hard water
Reduces cleansing power
✨ Quick Revision Points
Carbon forms covalent bonds
Allotropes: diamond, graphite, fullerene
Hydrocarbons → alkanes, alkenes, alkynes
Functional group decides properties
Soaps fail in hard water, detergents work
✍️ Top 10 Short Question–Answers
Q1. Why does carbon form covalent bonds?
Ans: Carbon cannot gain or lose four electrons easily, so it shares electrons to complete its octet.
Q2. What is a covalent bond?
Ans: A covalent bond is formed by mutual sharing of electron pairs between two atoms.
Q3. Name the types of covalent bonds.
Ans: Single bond, double bond and triple bond.
Q4. What is electron dot structure?
Ans: It shows valence electrons and shared electron pairs in a molecule.
Q5. What is allotropy?
Ans: The existence of an element in different physical forms with same chemical properties.
Q6. Name two allotropes of carbon.
Ans: Diamond and graphite.
Q7. What is catenation?
Ans: The self-linking property of carbon atoms to form chains and rings.
Q8. What are hydrocarbons?
Ans: Compounds containing only carbon and hydrogen.
Q9. What is a functional group?
Ans: An atom or group of atoms that determines chemical properties of a compound.
Q10. Why soaps do not work well in hard water?
Ans: Because they form scum with Ca²⁺ and Mg²⁺ ions.
📝 Long Answer Questions
Q1. Explain the versatile nature of carbon.
Ans:
Carbon forms a large number of compounds due to the following reasons:
Catenation:
Carbon atoms link with each other to form long straight, branched or ring chains.Tetravalency:
Carbon has valency four, so it forms four covalent bonds with other atoms.
Because of these properties, carbon forms millions of organic compounds.
Q2. Describe the allotropes of carbon.
Ans:
The different allotropes of carbon are:
Diamond:
Each carbon bonded to four carbon atoms
Hardest natural substance
Electrical insulator
Graphite:
Each carbon bonded to three carbon atoms
Good conductor of electricity
Used in pencils and as lubricant
Fullerene (C₆₀):
Spherical, football-like structure
Dark coloured solid
Q3. Differentiate between soaps and detergents.
Ans:
| Soap | Detergent |
|---|---|
| Made from fatty acids | Made from sulphonate salts |
| Biodegradable | Non-biodegradable |
| Ineffective in hard water | Effective in hard water |
| Forms scum | Does not form scum |
📝 PYQs (Previous Years’ Questions)
🔹 1 Mark PYQs
Why does carbon form covalent bonds?
What is a covalent bond?
Name the hardest allotrope of carbon.
Which allotrope of carbon conducts electricity?
What is a homologous series?
What is a functional group?
Write the general formula of alkanes.
Name the functional group present in ethanoic acid.
🔹 2 Marks PYQs
What is catenation? Why is carbon good at catenation?
Define saturated and unsaturated hydrocarbons.
What is allotropy? Name any two allotropes of carbon.
Write two physical properties of organic compounds.
Why detergents are better than soaps in hard water?
What is isomerism?
Write two uses of ethanol.
🔹 3 Marks PYQs
Explain the versatile nature of carbon.
Write differences between diamond and graphite.
Explain homologous series with its characteristics.
Write chemical properties of ethanol.
Explain the cleansing action of soap.
What happens when ethanoic acid reacts with:
(a) sodium hydroxide
(b) sodium carbonate
🔹 5 Marks PYQs (Long Answer Type)
Explain the properties of covalent compounds.
Describe the different allotropes of carbon.
Explain the formation of covalent bonds with electron dot structure.
Differentiate between soaps and detergents.
Explain the chemical properties of carbon compounds.
Describe esterification reaction with an example.
⭐ Very Important Repeated PYQs
✔ Why soaps do not work in hard water?
✔ Why carbon cannot form C⁴⁺ or C⁴⁻ ions?
✔ Why diamond is hard but graphite is soft?
✔ Why organic compounds are poor conductors of electricity?
✔ Identify the type of reaction:
Vegetable oil → vegetable ghee
❓ FAQs (Concept Clarity – 5)
Q1. Why organic compounds have low melting and boiling points?
Ans: Due to weak intermolecular forces between molecules.
Q2. Why diamond does not conduct electricity?
Ans: Because it has no free electrons.
Q3. Why unsaturated hydrocarbons burn with sooty flame?
Ans: Due to incomplete combustion.
Q4. Why detergents are preferred over soaps?
Ans: Because detergents work well even in hard water.
Q5. What causes scum formation?
Ans: Reaction of soap with calcium and magnesium ions of hard water.
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