Class 10th Science Chapter 4 – Carbon and Its Compounds | Saturated and Unsaturated Carbon Compounds

Class 10 Science – Chapter 4

Carbon and Its Compounds | कार्बन एवं उसके यौगिक

Saturated and Unsaturated Carbon Compounds | संतृप्त एवं असंतृप्त कार्बन यौगिक

CBSE + Foundation + Competitive Level

Saturated & Unsaturated Carbon Compounds

1. Basic Concept | मूल अवधारणा

English:
Carbon compounds are broadly classified as saturated and unsaturated depending on the type of carbon-carbon bonds present in them.

हिन्दी:
कार्बन यौगिकों को उनमें उपस्थित कार्बन-कार्बन बंध के प्रकार के आधार पर मुख्यतः संतृप्त और असंतृप्त यौगिकों में बाँटा जाता है।

Key Idea:
Only single C–C bonds → Saturated
At least one C=C or C≡C bond → Unsaturated

2. Saturated Carbon Compounds | संतृप्त कार्बन यौगिक

Definition:
Carbon compounds in which carbon atoms are connected only by single covalent bonds are called saturated carbon compounds.

परिभाषा:
वे कार्बन यौगिक जिनमें कार्बन परमाणुओं के बीच केवल एकल सहसंयोजक बंध (C–C) होते हैं, संतृप्त कार्बन यौगिक कहलाते हैं।

The simplest saturated hydrocarbons are called alkanes.

Methane: CH₄

Ethane: CH₃–CH₃

Propane: CH₃–CH₂–CH₃

Butane: CH₃–CH₂–CH₂–CH₃

3. General Formula of Alkanes | एल्केन का सामान्य सूत्र

CₙH₂ₙ₊₂

For open-chain saturated hydrocarbons:
General formula = CₙH₂ₙ₊₂

Examples:

Alkane	Formula	n
Methane	CH₄	1
Ethane	C₂H₆	2
Propane	C₃H₈	3
Butane	C₄H₁₀	4
Pentane	C₅H₁₂	5

4. Unsaturated Carbon Compounds | असंतृप्त कार्बन यौगिक

English:
Carbon compounds containing at least one double bond (C=C) or triple bond (C≡C) between carbon atoms are called unsaturated carbon compounds.

हिन्दी:
वे कार्बन यौगिक जिनमें कार्बन परमाणुओं के बीच कम-से-कम एक द्विबंध (C=C) या त्रिबंध (C≡C) उपस्थित हो, असंतृप्त कार्बन यौगिक कहलाते हैं।

Ethene: CH₂=CH₂

Propene: CH₃–CH=CH₂

Ethyne: HC≡CH

Propyne: CH₃–C≡CH

5. Alkenes | एल्कीन

Alkenes are unsaturated hydrocarbons containing at least one C=C double bond.

General formula for open-chain alkenes with one double bond:

CₙH₂ₙ

Ethene → C₂H₄ → CH₂=CH₂

Propene → C₃H₆ → CH₃–CH=CH₂

Butene → C₄H₈

6. Alkynes | एल्काइन

Alkynes are unsaturated hydrocarbons containing at least one C≡C triple bond.

General formula for open-chain alkynes with one triple bond:

CₙH₂ₙ₋₂

Ethyne → C₂H₂ → HC≡CH

Propyne → C₃H₄ → CH₃–C≡CH

Butyne → C₄H₆

7. Difference Between Saturated and Unsaturated Compounds

Property | गुण	Saturated | संतृप्त	Unsaturated | असंतृप्त
C–C bond	Only single bonds	At least one double or triple bond
Examples	Ethane, Propane	Ethene, Ethyne
Hydrocarbon family	Alkanes	Alkenes and Alkynes
General formula	CₙH₂ₙ₊₂	Alkenes: CₙH₂ₙ Alkynes: CₙH₂ₙ₋₂
Reactivity	Generally less reactive	Generally more reactive
Addition reaction	Generally do not undergo typical addition reactions	Readily undergo addition reactions

8. Why Are Unsaturated Compounds More Reactive?

Unsaturated compounds contain π (pi) bonds in addition to σ (sigma) bonds. The π bond is generally more reactive and can break during addition reactions, allowing new atoms or groups to attach to the carbon atoms.

हिन्दी:
असंतृप्त यौगिकों में σ बंध के साथ π बंध भी उपस्थित होता है। π बंध अधिक अभिक्रियाशील होता है और योगात्मक अभिक्रियाओं में टूटकर नए परमाणुओं या समूहों को जुड़ने का अवसर देता है।

9. Addition Reaction | योगात्मक अभिक्रिया

An addition reaction occurs when atoms or groups are added to an unsaturated compound across a double or triple bond.

CH₂=CH₂ + H₂ → CH₃–CH₃
Ethene + Hydrogen → Ethane

This reaction converts an unsaturated compound into a saturated compound.
यह अभिक्रिया असंतृप्त यौगिक को संतृप्त यौगिक में परिवर्तित करती है।

10. Hydrogenation | हाइड्रोजनीकरण

Hydrogenation is the addition of hydrogen to an unsaturated compound in the presence of a catalyst such as Ni, Pt or Pd.

Example:

CH₂=CH₂ + H₂
    Ni
↓
CH₃–CH₃

Hydrogenation is important in the conversion of vegetable oils into partially or fully hydrogenated fats.

11. Test for Unsaturation | असंतृप्तता की जाँच

Unsaturated compounds can be detected using bromine water. An unsaturated compound generally decolourises bromine water because bromine undergoes an addition reaction with the C=C or C≡C bond.

हिन्दी:
असंतृप्त यौगिक ब्रोमीन जल का रंग सामान्यतः हटा देते हैं क्योंकि ब्रोमीन C=C या C≡C बंध पर योग अभिक्रिया करता है।

Bromine water: Orange/Brown
↓
Unsaturated compound
↓
Decolourisation

12. Saturated vs Unsaturated – Bromine Water Test

Compound	Bond	Bromine Water
Ethane	C–C single	Generally no rapid decolourisation
Ethene	C=C double	Decolourises bromine water
Ethyne	C≡C triple	Can react with bromine and decolourise it

13. Complete Structural Comparison

Ethane – Saturated
CH₃–CH₃

Ethene – Unsaturated
CH₂=CH₂

Ethyne – Unsaturated
HC≡CH

Important:

• Ethane has only single C–C bond → saturated.
• Ethene has one C=C bond → unsaturated.
• Ethyne has one C≡C bond → unsaturated.

14. Homologous Series Connection | समजातीय श्रेणी

Saturated and unsaturated hydrocarbons form homologous series. Members of a homologous series:

• Have the same functional group or type of bonding pattern.
• Have similar chemical properties.
• Differ successively by a –CH₂– unit.
• Show a gradual change in physical properties.

CH₄ → C₂H₆ → C₃H₈ → C₄H₁₀
Difference between successive members = CH₂

15. Degree of Unsaturation – Foundation/Competitive

For an open-chain hydrocarbon:

• One C=C bond reduces hydrogen count by 2 compared with the corresponding alkane.
• One C≡C bond reduces hydrogen count by 4 compared with the corresponding alkane.

Example:

Ethane = C₂H₆
Ethene = C₂H₄
Ethyne = C₂H₂

Memory Trick:
Alkane → single bond → maximum H
Alkene → double bond → H₂ less
Alkyne → triple bond → H₄ less than corresponding alkane

16. 30 MCQs | बहुविकल्पीय प्रश्न

1. A saturated hydrocarbon contains:

A. Only single C–C bonds

B. Only double bonds

C. Only triple bonds

D. Ionic bonds

Answer: A

2. Which is a saturated hydrocarbon?

A. Ethene

B. Ethyne

C. Ethane

D. Propene

Answer: C

3. Which is an unsaturated hydrocarbon?

A. Methane

B. Ethane

C. Propane

D. Ethene

Answer: D

4. General formula of alkanes is:

A. CₙH₂ₙ

B. CₙH₂ₙ₊₂

C. CₙH₂ₙ₋₂

D. CₙHₙ

Answer: B

5. General formula of open-chain alkenes with one double bond is:

A. CₙH₂ₙ

B. CₙH₂ₙ₊₂

C. CₙH₂ₙ₋₂

D. CₙHₙ₊₂

Answer: A

6. General formula of open-chain alkynes with one triple bond is:

A. CₙH₂ₙ₊₂

B. CₙH₂ₙ

C. CₙH₂ₙ₋₂

D. CₙH₂ₙ₊₄

Answer: C

7. Ethene contains:

A. C–C

B. C=C

C. C≡C

D. C–O–C

Answer: B

8. Ethyne contains:

A. C–C

B. C=C

C. C≡C

D. C–H only

Answer: C

9. Which compound is an alkane?

A. C₂H₄

B. C₂H₂

C. C₃H₆

D. C₃H₈

Answer: D

10. Which compound is an alkene?

A. C₃H₈

B. C₃H₆

C. C₄H₁₀

D. CH₄

Answer: B

11. Which compound is an alkyne?

A. C₂H₂

B. C₂H₄

C. C₂H₆

D. CH₄

Answer: A

12. Unsaturated compounds generally contain:

A. Only σ bonds

B. π bond(s)

C. Ionic bonds only

D. Metallic bonds

Answer: B

13. Which compound can decolourise bromine water?

A. Ethane

B. Methane

C. Ethene

D. Propane

Answer: C

14. Addition of hydrogen to ethene gives:

A. Methane

B. Ethane

C. Ethyne

D. Propane

Answer: B

15. Hydrogenation generally requires:

A. NaCl

B. Ni/Pt/Pd catalyst

C. HCl only

D. Water only

Answer: B

16. Which has maximum hydrogen among the following?

A. C₂H₂

B. C₂H₄

C. C₂H₆

D. C₂H₅OH

Answer: C

17. Which is the saturated compound?

A. CH₂=CH₂

B. HC≡CH

C. CH₃–CH₃

D. CH₃–CH=CH₂

Answer: C

18. The suffix used for alkenes is:

A. -ane

B. -ene

C. -yne

D. -ol

Answer: B

19. The suffix used for alkynes is:

A. -yne

B. -ane

C. -ene

D. -ol

Answer: A

20. The suffix used for alkanes is:

A. -ene

B. -yne

C. -ane

D. -one

Answer: C

21. Which compound has a triple bond?

A. Ethane

B. Ethene

C. Ethyne

D. Methane

Answer: C

22. Which bond is present in ethene?

A. One C=C and C–H bonds

B. Only C–C single bonds

C. C≡C only

D. Ionic bond

Answer: A

23. Which is generally more reactive?

A. Saturated hydrocarbon

B. Unsaturated hydrocarbon

C. Noble gas

D. Alkali metal only

Answer: B

24. Which reaction converts an unsaturated compound into a saturated compound?

A. Addition of hydrogen

B. Neutralisation

C. Precipitation

D. Sublimation

Answer: A

25. C₄H₁₀ belongs to:

A. Alkane

B. Alkene

C. Alkyne

D. Alcohol

Answer: A

26. C₄H₈, for an open-chain hydrocarbon with one double bond, represents:

A. Alkane

B. Alkene

C. Alkyne

D. Methane

Answer: B

27. C₄H₆, for an open-chain hydrocarbon with one triple bond, represents:

A. Alkane

B. Alkene

C. Alkyne

D. Alcohol

Answer: C

28. A C=C bond contains:

A. One σ bond only

B. One σ and one π bond

C. Two π bonds only

D. Ionic bonds

Answer: B

29. A C≡C bond contains:

A. One σ and two π bonds

B. Three σ bonds

C. Two σ bonds only

D. One π bond only

Answer: A

30. Which statement is correct?

A. All hydrocarbons are saturated.

B. Alkanes contain C=C bonds.

C. Alkenes contain at least one C=C bond.

D. Alkynes contain only single bonds.

Answer: C

17. 30 Subjective Questions with Answers
वर्णनात्मक प्रश्न एवं उत्तर

1 Mark
Q1. What is a saturated carbon compound?

A carbon compound containing only single bonds between carbon atoms is called a saturated carbon compound.

1 Mark
Q2. What is an unsaturated carbon compound?

A carbon compound containing at least one C=C or C≡C bond is called an unsaturated carbon compound.

1 Mark
Q3. Give one example of a saturated hydrocarbon.

Ethane (C₂H₆).

1 Mark
Q4. Give one example of an unsaturated hydrocarbon.

Ethene (C₂H₄).

2 Marks
Q5. Differentiate between saturated and unsaturated compounds.

Saturated compounds contain only C–C single bonds, whereas unsaturated compounds contain at least one C=C or C≡C bond.

2 Marks
Q6. Write the general formula of alkanes and alkenes.

Alkanes: CₙH₂ₙ₊₂
Alkenes: CₙH₂ₙ

2 Marks
Q7. What are alkenes? Give one example.

Alkenes are unsaturated hydrocarbons containing at least one C=C bond. Example: Ethene (C₂H₄).

2 Marks
Q8. What are alkynes? Give one example.

Alkynes are unsaturated hydrocarbons containing at least one C≡C bond. Example: Ethyne (C₂H₂).

3 Marks
Q9. Explain saturated hydrocarbons with examples.

Saturated hydrocarbons contain only single covalent bonds between carbon atoms. They belong to the alkane family. Their general formula for open-chain compounds is CₙH₂ₙ₊₂. Examples are methane, ethane and propane.

3 Marks
Q10. Explain unsaturated hydrocarbons with examples.

Unsaturated hydrocarbons contain one or more C=C or C≡C bonds. Alkenes contain C=C bonds and alkynes contain C≡C bonds. Examples include ethene and ethyne.

3 Marks
Q11. Why are unsaturated hydrocarbons generally more reactive?

They contain π bonds, which are more reactive than σ bonds and can participate in addition reactions. Therefore unsaturated hydrocarbons generally undergo reactions more readily than alkanes.

3 Marks
Q12. Write the structures of ethane, ethene and ethyne.

Ethane: CH₃–CH₃

Ethene: CH₂=CH₂

Ethyne: HC≡CH

4 Marks
Q13. Explain the difference between alkanes, alkenes and alkynes.

Family	Bond	General Formula	Example
Alkanes	Single	CₙH₂ₙ₊₂	Ethane
Alkenes	Double	CₙH₂ₙ	Ethene
Alkynes	Triple	CₙH₂ₙ₋₂	Ethyne

4 Marks
Q14. Explain the addition reaction with an example.

In an addition reaction, atoms or groups are added across a double or triple bond.

CH₂=CH₂ + H₂ → CH₃–CH₃

Ethene reacts with hydrogen to form ethane in the presence of a suitable catalyst.

4 Marks
Q15. What is hydrogenation? Give its chemical equation.

Hydrogenation is the addition of hydrogen to an unsaturated compound in the presence of a catalyst such as Ni, Pt or Pd.

CH₂=CH₂ + H₂ → CH₃–CH₃
Catalyst: Ni

4 Marks
Q16. How can you distinguish between saturated and unsaturated compounds?

The bromine-water test can be used. An unsaturated compound generally decolourises bromine water due to an addition reaction, whereas a saturated hydrocarbon does not rapidly decolourise bromine water under ordinary test conditions.

4 Marks
Q17. Explain the role of π bonds in unsaturated compounds.

A double bond consists of one σ and one π bond, while a triple bond consists of one σ and two π bonds. The π bond is more exposed and reactive, so it participates readily in addition reactions. This contributes to the higher reactivity of unsaturated compounds.

5 Marks
Q18. Compare saturated and unsaturated hydrocarbons in detail.

Saturated	Unsaturated
Only single C–C bonds	At least one C=C or C≡C bond
Alkanes	Alkenes and alkynes
Generally less reactive	Generally more reactive
Do not usually undergo typical addition reactions	Readily undergo addition reactions
Example: Ethane	Examples: Ethene, Ethyne

5 Marks
Q19. Explain the general formulae of alkanes, alkenes and alkynes.

For open-chain hydrocarbons with the indicated single multiple bond:

Alkanes: CₙH₂ₙ₊₂
Only single bonds.

Alkenes: CₙH₂ₙ
One C=C double bond.

Alkynes: CₙH₂ₙ₋₂
One C≡C triple bond.

5 Marks
Q20. Explain why ethene is unsaturated while ethane is saturated.

Ethane has the structure CH₃–CH₃ and contains only a single C–C bond. Therefore it is saturated. Ethene has the structure CH₂=CH₂ and contains a C=C double bond. Therefore it is unsaturated.

5 Marks
Q21. Explain bromine-water test for unsaturation.

Bromine water has an orange/brown colour. An unsaturated compound reacts with bromine through an addition reaction across its multiple bond. As bromine is consumed, its colour disappears. Thus decolourisation of bromine water is used as a test for unsaturation.

5 Marks
Q22. Explain hydrogenation of vegetable oils.

Many vegetable oils contain unsaturated carbon-carbon bonds. Hydrogen can be added across these double bonds in the presence of a catalyst such as nickel. This increases saturation and can convert liquid oils into more solid or semi-solid fats. Industrial hydrogenation must be controlled carefully because partial hydrogenation can produce trans fats.

6 Marks
Q23. Explain saturated and unsaturated hydrocarbons with examples and formulae.

Saturated hydrocarbons:
They contain only single C–C bonds and are called alkanes. Their general formula is CₙH₂ₙ₊₂. Examples are methane, ethane and propane.

Unsaturated hydrocarbons:
They contain at least one double or triple bond. Alkenes contain C=C bonds and have the formula CₙH₂ₙ for open-chain compounds with one double bond. Alkynes contain C≡C bonds and have the formula CₙH₂ₙ₋₂ for open-chain compounds with one triple bond.

6 Marks
Q24. Describe the chemical behaviour of saturated and unsaturated hydrocarbons.

Saturated hydrocarbons generally contain strong C–C single bonds and are comparatively less reactive. They commonly undergo substitution reactions. Unsaturated hydrocarbons contain C=C or C≡C bonds and are generally more reactive. They readily undergo addition reactions. For example, ethene adds hydrogen in the presence of nickel to form ethane.

6 Marks
Q25. Explain addition and substitution reactions with suitable examples.

Addition reaction:
It occurs mainly in unsaturated compounds when atoms or groups add across a multiple bond.

CH₂=CH₂ + H₂ → CH₃–CH₃

Substitution reaction:
In saturated hydrocarbons, one atom or group can be replaced by another atom or group. Example:
CH₄ + Cl₂ → CH₃Cl + HCl
The reaction occurs in the presence of sunlight.

6 Marks
Q26. Explain the structures and bonding in ethane, ethene and ethyne.

Ethane: CH₃–CH₃
Contains a C–C single bond.

Ethene: CH₂=CH₂
Contains one C=C double bond consisting of one σ and one π bond.

Ethyne: HC≡CH
Contains one C≡C triple bond consisting of one σ and two π bonds.

6 Marks
Q27. Why does the hydrogen content decrease from alkane to alkene and alkyne?

An alkane contains only single bonds and therefore has the maximum possible number of hydrogen atoms for an open-chain hydrocarbon. When a C=C double bond is formed, two fewer hydrogen atoms are present compared with the corresponding alkane. When a C≡C triple bond is formed, four fewer hydrogen atoms are present compared with the corresponding alkane.

For two carbon atoms:
C₂H₆ → C₂H₄ → C₂H₂
Ethane → Ethene → Ethyne

6 Marks
Q28. A hydrocarbon has molecular formula C₄H₈. Can it be an alkane? Explain.

For an open-chain alkane, the general formula is CₙH₂ₙ₊₂. For n = 4:
C₄H₁₀
Therefore C₄H₈ does not fit the alkane formula. If it is an open-chain hydrocarbon with one double bond, it fits the alkene formula CₙH₂ₙ and can represent an alkene such as butene.

6 Marks
Q29. A hydrocarbon decolourises bromine water. What can you infer about its structure?

The decolourisation suggests that the hydrocarbon is unsaturated and contains a reactive multiple bond, generally C=C or C≡C, under the test conditions. Bromine adds across the multiple bond, consuming bromine and causing the colour to disappear.

6 Marks
Q30. Give a complete comparison of alkanes, alkenes and alkynes.

Feature	Alkanes	Alkenes	Alkynes
Nature	Saturated	Unsaturated	Unsaturated
Characteristic bond	C–C	C=C	C≡C
General formula	CₙH₂ₙ₊₂	CₙH₂ₙ	CₙH₂ₙ₋₂
Example	Ethane	Ethene	Ethyne
Typical reaction	Substitution	Addition	Addition
Reactivity	Generally lower	Generally higher	Generally higher

18. Quick Revision | त्वरित पुनरावृत्ति

• Saturated: Only C–C single bonds.
  संतृप्त: केवल एकल C–C बंध।
• Unsaturated: At least one C=C or C≡C bond.
  असंतृप्त: कम-से-कम एक द्विबंध या त्रिबंध।
• Alkanes: CₙH₂ₙ₊₂
• Alkenes: CₙH₂ₙ
• Alkynes: CₙH₂ₙ₋₂
• Ethane: CH₃–CH₃
• Ethene: CH₂=CH₂
• Ethyne: HC≡CH
• Double bond: 1 σ + 1 π
• Triple bond: 1 σ + 2 π
• Unsaturation test: Bromine water decolourisation.
• Hydrogenation: Addition of H₂ to unsaturated compounds.

19. CBSE Exam Tips | परीक्षा उपयोगी बिंदु

Remember:

1. Never call a compound saturated merely because it contains hydrogen.
2. Check the C–C bonds.
3. Only single C–C bonds → saturated.
4. C=C or C≡C → unsaturated.
5. Alkanes → CₙH₂ₙ₊₂.
6. Alkenes → CₙH₂ₙ for open-chain compounds with one double bond.
7. Alkynes → CₙH₂ₙ₋₂ for open-chain compounds with one triple bond.
8. Unsaturated compounds generally undergo addition reactions.
9. Alkanes commonly undergo substitution reactions.

One-Line Memory Trick:
SINGLE = SATURATED | DOUBLE/TRIPLE = UNSATURATED
एकल = संतृप्त | द्वि/त्रि = असंतृप्त

Class 10th Science Chapter 4 – Carbon and Its Compounds | Properties of Covalent Compounds

Carbon and Its Compounds

Properties of Covalent Compounds | कार्बन एवं उसके यौगिक

CBSE + Foundation + Competitive Level

Properties of Covalent Compounds | सहसंयोजक यौगिकों के गुण

1. Introduction | परिचय

English:
Covalent compounds are compounds formed by the sharing of electrons between atoms. Carbon forms a large number of covalent compounds because it has tetravalency and a strong tendency to form bonds with carbon and other elements.

हिन्दी:
सहसंयोजक यौगिक वे यौगिक हैं जिनमें परमाणु इलेक्ट्रॉनों की साझेदारी करके बंध बनाते हैं। कार्बन अपनी चतुसंयोजकता तथा कार्बन और अन्य तत्वों के साथ मजबूत बंध बनाने की क्षमता के कारण बड़ी संख्या में सहसंयोजक यौगिक बनाता है।

2. Main Properties of Covalent Compounds | सहसंयोजक यौगिकों के प्रमुख गुण

Covalent compounds generally show the following properties:

मुख्य गुण:

• Generally have low melting and boiling points.
• Usually exist as gases, liquids or soft solids.
• Generally do not conduct electricity.
• Usually have weak intermolecular forces.
• Many are insoluble in water but soluble in organic solvents.
• They are generally molecular in nature.
• They may have characteristic odours.

3. Low Melting and Boiling Points | निम्न गलनांक एवं क्वथनांक

English:
Most covalent compounds have low melting and boiling points because the forces of attraction between their molecules are generally weak. For example, methane (CH₄), carbon dioxide (CO₂) and ammonia (NH₃) are molecular covalent substances.

हिन्दी:
अधिकांश सहसंयोजक यौगिकों के गलनांक और क्वथनांक कम होते हैं क्योंकि उनके अणुओं के बीच आकर्षण बल सामान्यतः कमजोर होते हैं।

Important: Covalent bonds inside a molecule are strong, but the forces between separate molecules are often weak. Therefore, many molecular covalent substances have low melting and boiling points.
महत्वपूर्ण: अणु के अंदर सहसंयोजक बंध मजबूत होते हैं, लेकिन अलग-अलग अणुओं के बीच बल अक्सर कमजोर होते हैं।

4. Important Exceptions | महत्वपूर्ण अपवाद

Not every covalent substance has a low melting point. Diamond and silicon dioxide (SiO₂) have very high melting points because they form giant covalent/network structures.

हीरा और सिलिकॉन डाइऑक्साइड (SiO₂) जैसे पदार्थों में विशाल सहसंयोजक संरचना होती है, इसलिए इनके गलनांक बहुत अधिक होते हैं।

5. Physical State | भौतिक अवस्था

Substance | पदार्थ	State | अवस्था	Example | उदाहरण
Gas | गैस	Many covalent compounds are gases.	CH₄, CO₂, NH₃
Liquid | द्रव	Some covalent compounds are liquids.	Ethanol, benzene
Solid | ठोस	Some are solids.	Sugar, iodine, naphthalene
Network solid | जालक ठोस	Very hard and high melting.	Diamond, SiO₂

6. Electrical Conductivity | विद्युत चालकता

English:
Covalent compounds generally do not conduct electricity because they do not contain free ions or freely moving charged particles.

हिन्दी:
सहसंयोजक यौगिक सामान्यतः विद्युत का चालन नहीं करते क्योंकि इनमें स्वतंत्र आयन या स्वतंत्र रूप से गतिशील आवेशित कण नहीं होते।

Covalent compound → No free ions → Generally poor conductor

Exception: Graphite conducts electricity because it contains delocalised electrons.
अपवाद: ग्रेफाइट विद्युत का चालन करता है क्योंकि इसमें विस्थानीकृत (delocalised) इलेक्ट्रॉन होते हैं।

7. Solubility | विलेयता

Covalent compounds are generally insoluble or only slightly soluble in water. Many covalent compounds are soluble in organic solvents such as benzene, ether and carbon tetrachloride.

हिन्दी:
सहसंयोजक यौगिक सामान्यतः जल में अघुलनशील या बहुत कम घुलनशील होते हैं। कई सहसंयोजक यौगिक कार्बनिक विलायकों में घुलनशील होते हैं।

General rule: "Like dissolves like" — समान प्रकृति वाले पदार्थ एक-दूसरे में अधिक घुलते हैं।

8. Intermolecular Forces | अंतराअणुक बल

Molecular covalent compounds are held together in the solid or liquid state by intermolecular forces. These forces are generally weaker than ionic or network covalent bonds.

हिन्दी:
अणुक सहसंयोजक यौगिकों के अणुओं के बीच अंतराअणुक बल कार्य करते हैं। ये बल सामान्यतः आयनिक बंध या विशाल सहसंयोजक जालक के बंधों की तुलना में कमजोर होते हैं।

9. Hardness | कठोरता

Most molecular covalent compounds are soft because their molecules are held together by weak intermolecular forces. However, giant covalent structures such as diamond are extremely hard.

Example: Diamond is one of the hardest naturally occurring substances.

10. Covalent Compounds vs Ionic Compounds
सहसंयोजक एवं आयनिक यौगिकों में अंतर

Property | गुण	Covalent | सहसंयोजक	Ionic | आयनिक
Formation	Sharing of electrons	Transfer of electrons
Particles	Usually molecules	Ions
Melting point	Generally low	Generally high
Boiling point	Generally low	Generally high
Electrical conduction	Generally poor	Conduct when molten or dissolved in water
Solubility	Often soluble in organic solvents	Often soluble in water
Physical nature	Many gases/liquids/soft solids	Generally hard crystalline solids

11. Why Do Covalent Compounds Generally Not Conduct Electricity?
सहसंयोजक यौगिक सामान्यतः विद्युत का चालन क्यों नहीं करते?

English:

• Electric current requires moving charged particles.
• Covalent compounds generally consist of neutral molecules.
• They do not normally produce free ions.
• Therefore, they generally do not conduct electricity.

हिन्दी:

• विद्युत धारा के लिए गतिशील आवेशित कण आवश्यक होते हैं।
• सहसंयोजक यौगिक सामान्यतः उदासीन अणुओं से बने होते हैं।
• इनमें स्वतंत्र आयन सामान्यतः नहीं होते।
• इसलिए ये सामान्यतः विद्युत का चालन नहीं करते।

12. Diamond and Graphite | हीरा एवं ग्रेफाइट

Property	Diamond	Graphite
Structure	Each carbon bonded strongly in 3D network.	Carbon atoms arranged in layers.
Hardness	Extremely hard	Soft
Electrical conductivity	Does not conduct electricity	Conducts electricity
Reason	No freely moving electrons	Delocalised electrons are present

13. Giant Covalent Structures | विशाल सहसंयोजक संरचनाएँ

A giant covalent structure contains a very large number of atoms connected by strong covalent bonds. Examples:

• Diamond
• Graphite
• Silicon dioxide (SiO₂)

These substances generally have:

• Very high melting points
• High hardness in many cases
• Strong covalent bonds throughout the structure

14. 30 MCQs | बहुविकल्पीय प्रश्न

1. Covalent compounds are formed by:
सहसंयोजक यौगिक बनते हैं:

A. Transfer of electrons

B. Sharing of electrons

C. Loss of protons

D. Gain of neutrons

Answer: B — Electrons are shared between atoms.

2. Covalent compounds generally have:
सहसंयोजक यौगिकों का सामान्यतः होता है:

A. Low melting point

B. Very high melting point

C. No melting point

D. Infinite melting point

Answer: A

3. Most covalent compounds are poor conductors because they lack:

A. Atoms

B. Molecules

C. Free charged particles

D. Covalent bonds

Answer: C

4. Which allotrope of carbon conducts electricity?

A. Diamond

B. Graphite

C. Fullerene only

D. Coal

Answer: B

5. Diamond has a high melting point mainly because:

A. It contains ions

B. It has weak forces

C. It contains a giant covalent network

D. It contains water

Answer: C

6. Which is generally a covalent compound?

A. NaCl

B. MgO

C. CH₄

D. KBr

Answer: C

7. Covalent compounds generally consist of:

A. Neutral molecules

B. Only positive ions

C. Only negative ions

D. Free protons

Answer: A

8. Which substance is extremely hard?

A. Graphite

B. Diamond

C. Wax

D. Methane

Answer: B

9. Which compound is a gas at room temperature?

A. Methane

B. Sodium chloride

C. Calcium carbonate

D. Copper

Answer: A

10. Which statement is correct?

A. All covalent compounds are gases.

B. All covalent compounds conduct electricity.

C. Molecular covalent compounds often have low boiling points.

D. All covalent compounds are ionic.

Answer: C

11. Which has delocalised electrons?

A. Diamond

B. Graphite

C. Methane

D. Ethane

Answer: B

12. Silicon dioxide is an example of:

A. Ionic liquid

B. Giant covalent structure

C. Metallic compound

D. Simple ion

Answer: B

13. Which force is generally weak between molecular covalent molecules?

A. Intermolecular force

B. Nuclear force

C. Strong covalent bond

D. Proton force

Answer: A

14. Covalent compounds are often soluble in:

A. Organic solvents

B. Molten metals

C. Iron

D. Copper

Answer: A

15. Which is NOT generally a property of molecular covalent compounds?

A. Low boiling point

B. Poor electrical conductivity

C. Presence of free ions

D. Weak intermolecular forces

Answer: C

16. Graphite conducts electricity due to:

A. Free protons

B. Delocalised electrons

C. Sodium ions

D. Water molecules

Answer: B

17. Diamond is:

A. Soft and a good conductor

B. Hard and generally an electrical insulator

C. Ionic

D. Metallic

Answer: B

18. Which property is due mainly to weak intermolecular forces?

A. Low boiling point

B. High nuclear charge

C. Atomic number

D. Proton number

Answer: A

19. Which contains a giant covalent structure?

A. CH₄

B. CO₂

C. Diamond

D. H₂

Answer: C

20. Ionic compounds conduct electricity in molten state because:

A. Molecules disappear

B. Ions become free to move

C. Covalent bonds form

D. Atoms become neutral

Answer: B

21. A molecular covalent substance usually has:

A. Weak intermolecular forces

B. Only ionic bonds

C. Free electrons everywhere

D. Metallic bonding

Answer: A

22. Which is a network covalent solid?

A. Diamond

B. Methane

C. Ethane

D. Ammonia

Answer: A

23. Covalent compounds generally do not have:

A. Molecules

B. Shared electrons

C. Free ions

D. Covalent bonds

Answer: C

24. Which statement about diamond is correct?

A. It has weak intermolecular forces only.

B. It has a strong three-dimensional covalent network.

C. It is a metal.

D. It contains Na⁺ ions.

Answer: B

25. Which one generally has a higher melting point?

A. Molecular covalent compound

B. Giant covalent solid

C. Methane

D. Ethane

Answer: B

26. Which is an example of a molecular covalent compound?

A. CH₄

B. NaCl

C. MgCl₂

D. CaO

Answer: A

27. Most covalent compounds are poor conductors because:

A. They contain no atoms.

B. Their electrons are not available as free charge carriers.

C. They contain only metals.

D. They contain protons only.

Answer: B

28. Which substance is soft because of its layered structure?

A. Diamond

B. Graphite

C. SiO₂

D. Silicon carbide

Answer: B

29. Low boiling points of many covalent compounds are associated with:

A. Strong ionic lattice

B. Weak intermolecular forces

C. Free ions

D. Metallic bonds

Answer: B

30. Which pair contains covalent substances?

A. CH₄ and CO₂

B. NaCl and KCl

C. MgO and CaO

D. NaOH and KOH

Answer: A

15. 30 Subjective Questions with Answers
वर्णनात्मक प्रश्न एवं उत्तर

1 Mark
Q1. What is a covalent compound?
सहसंयोजक यौगिक क्या है?

A compound formed by sharing of electrons between atoms is called a covalent compound.
इलेक्ट्रॉनों की साझेदारी से बनने वाले यौगिक को सहसंयोजक यौगिक कहते हैं।

1 Mark
Q2. Why do covalent compounds generally have low melting points?

Because the intermolecular forces between their molecules are generally weak.
क्योंकि इनके अणुओं के बीच अंतराअणुक बल सामान्यतः कमजोर होते हैं।

1 Mark
Q3. Name one covalent compound that conducts electricity.

Graphite is a covalent form of carbon that conducts electricity.

1 Mark
Q4. Give one example of a giant covalent substance.

Diamond or silicon dioxide (SiO₂).

2 Marks
Q5. Why are covalent compounds generally poor conductors of electricity?

They generally do not contain free ions or freely moving charged particles.
इनमें सामान्यतः स्वतंत्र आयन या स्वतंत्र रूप से गतिशील आवेशित कण नहीं होते।

2 Marks
Q6. State two properties of covalent compounds.

1. Generally low melting and boiling points.
2. Generally poor electrical conductivity.

2 Marks
Q7. Why are many covalent compounds soluble in organic solvents?

Many covalent compounds and organic solvents have similar molecular/non-polar characteristics, so they dissolve more readily in each other.

2 Marks
Q8. Why does diamond have a high melting point?

Diamond has a giant three-dimensional network of strong covalent bonds. A large amount of energy is required to break these bonds.

3 Marks
Q9. Explain three properties of molecular covalent compounds.

1. Low melting and boiling points.
2. Poor electrical conductivity.
3. Many are soluble in organic solvents and have limited solubility in water.

3 Marks
Q10. Differentiate between molecular covalent and giant covalent substances.

Molecular covalent: Consist of separate molecules; generally low melting points; weak intermolecular forces.

Giant covalent: Atoms are connected throughout a large network; generally very high melting points; strong covalent bonds throughout.

3 Marks
Q11. Explain why graphite conducts electricity but diamond does not.

In graphite, some electrons are delocalised and can move through the layers, allowing electrical conduction. In diamond, all valence electrons are involved in strong covalent bonds, so there are no freely moving electrons.

3 Marks
Q12. Write three differences between covalent and ionic compounds.

• Covalent compounds involve electron sharing; ionic compounds involve electron transfer.
• Covalent compounds generally have lower melting points; ionic compounds generally have higher melting points.
• Covalent compounds generally do not conduct electricity; ionic compounds conduct when molten or dissolved.

4 Marks
Q13. Explain the electrical conductivity of covalent compounds.

Covalent compounds generally consist of neutral molecules. Their electrons are involved in covalent bonds and they generally do not produce free ions. Since electrical conduction requires mobile charged particles, most covalent compounds are poor conductors. Graphite is an exception because it contains delocalised electrons.

4 Marks
Q14. Explain the melting and boiling points of covalent compounds.

Most molecular covalent compounds have weak intermolecular forces. Therefore, only a small amount of energy is needed to separate their molecules, resulting in low melting and boiling points. Giant covalent substances such as diamond are exceptions because strong covalent bonds extend throughout their structures.

4 Marks
Q15. Explain the solubility behaviour of covalent compounds.

Most covalent compounds are generally insoluble or slightly soluble in water. Many are soluble in organic solvents because substances with similar molecular characteristics tend to dissolve in each other. The exact solubility depends on polarity and intermolecular interactions.

4 Marks
Q16. Compare diamond and graphite.

Diamond	Graphite
Three-dimensional covalent network	Layered structure
Very hard	Soft
Does not conduct electricity	Conducts electricity
All valence electrons participate in bonding	Delocalised electrons are present

4 Marks
Q17. Why are giant covalent substances generally hard and have high melting points?

They contain a huge network of atoms joined by strong covalent bonds. Breaking or disrupting this network requires a very large amount of energy. Hence they are generally hard and have high melting points.

5 Marks
Q18. Describe the important physical properties of covalent compounds.

Important properties include:

1. Generally low melting and boiling points for molecular substances.
2. Usually poor electrical conductivity.
3. Many are gases, liquids or soft solids.
4. Many are soluble in organic solvents.
5. Giant covalent substances are exceptions and may be extremely hard with high melting points.

5 Marks
Q19. Explain why molecular covalent compounds have low melting points while diamond has a high melting point.

Molecular covalent compounds consist of separate molecules held together by relatively weak intermolecular forces. Therefore, little energy is required to separate molecules. Diamond, however, has a giant three-dimensional network in which carbon atoms are connected by strong covalent bonds. Breaking this network requires enormous energy, giving diamond a very high melting point.

5 Marks
Q20. Explain the electrical behaviour of diamond and graphite.

Diamond does not conduct electricity because each carbon atom forms four covalent bonds and there are no freely moving electrons. Graphite conducts electricity because each carbon atom forms three bonds and one electron remains available for delocalisation. These delocalised electrons can move through the layers and carry electric charge.

5 Marks
Q21. Explain five general properties of covalent compounds.

1. Generally low melting points.
2. Generally low boiling points.
3. Poor electrical conductivity.
4. Often soluble in organic solvents.
5. Usually exist as gases, liquids or soft solids when molecular.

6 Marks
Q22. Discuss the properties of covalent compounds in detail.

Covalent compounds are formed by sharing electrons. Their major properties are:

• Most molecular covalent compounds have low melting and boiling points.
• They generally do not conduct electricity.
• They usually do not contain free ions.
• Many have limited solubility in water.
• Many dissolve in organic solvents.
• Giant covalent substances such as diamond and SiO₂ have high melting points because of strong covalent networks.

6 Marks
Q23. Compare covalent compounds with ionic compounds on the basis of six properties.

Property	Covalent	Ionic
Bond formation	Sharing of electrons	Transfer of electrons
Particles	Molecules	Ions
Melting point	Generally low	Generally high
Boiling point	Generally low	Generally high
Electrical conduction	Generally poor	Molten/aqueous state conducts
Physical state	Gas/liquid/soft solid often	Generally crystalline solid

6 Marks
Q24. Explain the structure-property relationship in diamond and graphite.

Diamond has a three-dimensional network in which each carbon atom is strongly bonded to four other carbon atoms. This makes diamond extremely hard and gives it a high melting point. It does not conduct electricity because there are no free electrons. Graphite has carbon atoms arranged in layers. Each carbon atom is bonded to three neighbouring carbon atoms, leaving one electron delocalised. The layers can slide over one another, making graphite soft, and the delocalised electrons allow it to conduct electricity.

6 Marks
Q25. Explain why most covalent compounds are poor conductors but graphite is a good conductor.

Most covalent compounds contain neutral molecules and their electrons are strongly associated with individual covalent bonds. There are no freely moving ions or charge carriers. Hence they generally do not conduct electricity. Graphite has a special layered structure. Each carbon atom forms three covalent bonds, while one electron per carbon atom becomes delocalised. These electrons can move through the structure and carry electric charge. Therefore graphite conducts electricity.

6 Marks
Q26. Discuss molecular covalent compounds and giant covalent compounds with examples.

Molecular covalent compounds: They consist of separate molecules. The molecules are held together by relatively weak intermolecular forces. They generally have low melting and boiling points. Examples include methane, carbon dioxide and ammonia.

Giant covalent compounds: They contain a continuous network of atoms joined by strong covalent bonds. They generally have high melting points. Examples include diamond and silicon dioxide.

6 Marks
Q27. Why are covalent compounds generally insoluble in water?

Many covalent compounds are non-polar or have weak interactions with water. Water is a polar solvent and therefore tends to dissolve polar or ionic substances more effectively. Many non-polar covalent substances do not interact strongly enough with water molecules to dissolve. However, polar covalent substances can be soluble in water, so this is a general trend rather than an absolute rule.

6 Marks
Q28. Explain the importance of intermolecular forces in covalent compounds.

Intermolecular forces act between separate molecules. In many molecular covalent compounds these forces are weaker than the covalent bonds within the molecules. Their strength affects physical properties such as melting point, boiling point, viscosity and physical state. Weak intermolecular forces often lead to low melting and boiling points.

6 Marks
Q29. A substance has a very high melting point and is extremely hard. It does not conduct electricity. Is it likely to be a molecular covalent compound? Explain.

No. These properties suggest a giant covalent structure such as diamond rather than a simple molecular covalent substance. Molecular covalent compounds generally have low melting points and are soft or volatile. Diamond has a strong three-dimensional covalent network, giving it high hardness and high melting point, while the absence of free electrons makes it a poor electrical conductor.

6 Marks
Q30. Give a comprehensive account of the properties of covalent compounds with suitable examples.

Covalent compounds are formed through sharing of electrons. Molecular covalent compounds generally have low melting and boiling points due to weak intermolecular forces. They are usually poor electrical conductors because they lack free ions or freely moving charge carriers. Many are insoluble or slightly soluble in water but dissolve in organic solvents. They can occur as gases, liquids or soft solids. However, giant covalent substances such as diamond and silicon dioxide are exceptions. They contain strong covalent bonds throughout a large network, so they have high melting points. Graphite is another special case because it contains delocalised electrons and therefore conducts electricity.

16. Quick Revision | त्वरित पुनरावृत्ति

Remember these key points:

• Covalent bond: Sharing of electrons.
• Molecular covalent compounds: Usually low melting and boiling points.
• Electrical conductivity: Generally poor.
• Reason: Absence of free ions/mobile charge carriers.
• Solubility: Many are soluble in organic solvents.
• Diamond: Giant covalent structure, very hard, high melting point.
• Graphite: Layered structure, soft and electrically conducting.
• SiO₂: Giant covalent structure.
• Important exception: Not every covalent substance has low melting point.

17. Foundation + Competitive Key Concept

Concept: The statement "covalent compounds have low melting points" should not be treated as an absolute rule.

Correct scientific understanding:

• Simple molecular covalent substances → generally low melting/boiling points.
• Giant covalent substances → generally very high melting points.
• Graphite → covalent network with electrical conductivity due to delocalised electrons.
• Diamond → giant covalent network and electrical insulator.

CBSE Exam Tip: Always write "generally" when describing the properties of covalent compounds because diamond, graphite and SiO₂ show important exceptions.

Class 10th Science Chapter 4 – Carbon and Its Compounds | Covalent Bonding and Electron-Dot Structures

🧪 Carbon and Its Compounds

Covalent Bonding and Electron-Dot Structures

Class 10 Science | CBSE + Foundation + Competitive Level

🔗 Covalent Bonding & Electron-Dot Structures

1. What is a Covalent Bond? | सहसंयोजक बंध क्या है?

English:
A covalent bond is a chemical bond formed by the sharing of one or more pairs of electrons between atoms. Covalent bonds are generally formed between non-metal atoms.

हिन्दी:
दो परमाणुओं के बीच एक या अधिक इलेक्ट्रॉन युग्मों की साझेदारी से बनने वाले रासायनिक बंध को सहसंयोजक बंध (Covalent Bond) कहते हैं। यह बंध सामान्यतः अधातु परमाणुओं के बीच बनता है।

2. Why Does Carbon Form Covalent Bonds?

Carbon has atomic number 6 and electronic configuration:

2, 4

Carbon has four electrons in its outermost shell. It would require a large amount of energy to remove all four valence electrons. Similarly, gaining four electrons would also be difficult and would result in an unstable highly charged ion. Therefore, carbon achieves stability mainly by sharing electrons. Hence, carbon forms covalent bonds.

हिन्दी:
कार्बन के बाह्यतम कोश में चार इलेक्ट्रॉन होते हैं। चार इलेक्ट्रॉनों को खोना या चार इलेक्ट्रॉनों को ग्रहण करना ऊर्जात्मक रूप से अनुकूल नहीं है। इसलिए कार्बन अन्य परमाणुओं के साथ इलेक्ट्रॉनों की साझेदारी करके अपना अष्टक पूरा करता है और सहसंयोजक बंध बनाता है।

3. Types of Covalent Bonds | सहसंयोजक बंध के प्रकार

Type	Shared Electron Pairs	Example
Single Covalent Bond	1 pair	H₂, CH₄, C₂H₆
Double Covalent Bond	2 pairs	O₂, C₂H₄
Triple Covalent Bond	3 pairs	N₂, C₂H₂

हिन्दी:

• एक इलेक्ट्रॉन युग्म की साझेदारी → एकल बंध
• दो इलेक्ट्रॉन युग्मों की साझेदारी → द्विबंध
• तीन इलेक्ट्रॉन युग्मों की साझेदारी → त्रिबंध

4. Electron-Dot Structure | इलेक्ट्रॉन-बिंदु संरचना

An electron-dot structure represents the valence electrons of atoms using dots. Shared electrons are shown between the atoms. The electron-dot structure helps us understand how atoms achieve stable electronic configurations.

हिन्दी:
परमाणु के संयोजकता इलेक्ट्रॉनों को बिंदुओं द्वारा दर्शाने वाली संरचना को इलेक्ट्रॉन-बिंदु संरचना कहते हैं। इससे यह समझने में सहायता मिलती है कि परमाणु इलेक्ट्रॉनों की साझेदारी करके स्थिर इलेक्ट्रॉनिक विन्यास कैसे प्राप्त करते हैं।

5. Electron-Dot Structure of Hydrogen (H₂)

Each hydrogen atom has one electron. Two hydrogen atoms share one pair of electrons.

H : H

This represents one shared electron pair. Therefore:

H—H

is a single covalent bond.
हिन्दी:
प्रत्येक हाइड्रोजन परमाणु में एक इलेक्ट्रॉन होता है। दो हाइड्रोजन परमाणु एक इलेक्ट्रॉन युग्म की साझेदारी करते हैं।

6. Electron-Dot Structure of Chlorine (Cl₂)

Each chlorine atom has seven valence electrons. Each chlorine atom needs one more electron to complete its octet. Therefore, two chlorine atoms share one pair of electrons.

Cl : Cl

Thus:

Cl—Cl

is formed.

7. Electron-Dot Structure of Oxygen (O₂)

Oxygen has six valence electrons. Each oxygen atom needs two more electrons to complete its octet. Therefore, the two oxygen atoms share two pairs of electrons.

O :: O

Thus oxygen contains a double covalent bond:

O=O

8. Electron-Dot Structure of Nitrogen (N₂)

Nitrogen has five valence electrons. Each nitrogen atom requires three more electrons to complete its octet. Therefore, two nitrogen atoms share three pairs of electrons.

N ::: N

Thus:

N≡N

Nitrogen contains a triple covalent bond.

9. Covalent Bond in Methane (CH₄)

Carbon has four valence electrons. Each hydrogen has one valence electron. Carbon shares one electron with each of four hydrogen atoms. Thus, four C–H covalent bonds are formed.

    H
    :
H : C : H
    :
    H

Simplified structural representation:

    H
    |
H—C—H
    |
    H

10. Covalent Bond in Ethane (C₂H₆)

Ethane contains two carbon atoms. The two carbon atoms share one pair of electrons with each other. Each carbon then forms three C–H bonds.

CH₃—CH₃

There are:

• One C–C single bond
• Six C–H single bonds

Total covalent bonds = 7.

11. Covalent Bond in Ethene (C₂H₄)

In ethene, the two carbon atoms share two pairs of electrons. Therefore, a carbon-carbon double bond is formed.

CH₂=CH₂

Each carbon also forms two C–H bonds. Thus ethene contains a C=C double bond.

12. Covalent Bond in Ethyne (C₂H₂)

In ethyne, the two carbon atoms share three pairs of electrons. Therefore, a carbon-carbon triple bond is formed.

HC≡CH

Each carbon forms one additional C–H bond. Thus ethyne contains a C≡C triple bond.

13. Important Properties of Covalent Compounds

Property	Explanation
Low melting and boiling points	Generally due to weak intermolecular forces.
Poor conductors of electricity	They generally do not have free ions or electrons.
Usually insoluble in water	Many covalent compounds are non-polar or less polar.
Often soluble in organic solvents	Many dissolve in non-polar organic solvents.

Important Exception:
Some covalent substances have very high melting points because they form giant covalent structures. Examples include diamond and silicon dioxide (SiO₂).

महत्वपूर्ण: सभी सहसंयोजक पदार्थों का melting point कम होना अनिवार्य नहीं है। हीरा और SiO₂ जैसे विशाल सहसंयोजक जालक बहुत कठोर होते हैं और इनके melting points बहुत अधिक होते हैं।

14. Covalent Compounds Do Not Conduct Electricity

Most covalent compounds do not conduct electricity because they do not contain freely moving charged particles such as ions. For example, sugar solution does not conduct electricity appreciably because sugar molecules do not ionise into ions.

हिन्दी:
अधिकांश सहसंयोजक यौगिक विद्युत के कुचालक होते हैं क्योंकि उनमें स्वतंत्र रूप से गति करने वाले आयन या इलेक्ट्रॉन नहीं होते। उदाहरण: चीनी का विलयन विद्युत का अच्छा चालक नहीं है।

15. Covalent Bond vs Ionic Bond

Covalent Bond	Ionic Bond
Electrons are shared.	Electrons are transferred.
Usually between non-metals.	Usually between metal and non-metal.
Forms molecules in many cases.	Forms ions and ionic lattices.
Generally poor electrical conductors.	Conduct electricity in molten/aqueous state.
Example: CH₄	Example: NaCl

16. Why Electron-Dot Structures Are Important?

Electron-dot structures help us determine:

• Number of valence electrons
• Number of shared electrons
• Number of covalent bonds
• Completion of octet or duplet
• Bond arrangement in molecules

हिन्दी:
इलेक्ट्रॉन-बिंदु संरचना से संयोजकता इलेक्ट्रॉन, साझे इलेक्ट्रॉन, बंधों की संख्या तथा अष्टक/द्विक की पूर्ति को समझना आसान होता है।

17. Octet Rule | अष्टक नियम

Atoms generally tend to achieve a stable configuration of eight electrons in their valence shell. This is called the octet rule. Hydrogen is an important exception because it becomes stable with two electrons — the duplet rule.

हिन्दी:
परमाणु सामान्यतः अपने बाह्यतम कोश में 8 इलेक्ट्रॉनों का स्थिर विन्यास प्राप्त करने का प्रयास करते हैं। इसे अष्टक नियम कहते हैं। हाइड्रोजन के लिए 2 इलेक्ट्रॉनों का स्थिर विन्यास पर्याप्त होता है, जिसे द्विक नियम कहते हैं।

18. Quick Comparison of Common Molecules

Molecule	Bond	Bond Type
H₂	H—H	Single
Cl₂	Cl—Cl	Single
O₂	O=O	Double
N₂	N≡N	Triple
CH₄	C—H	Single covalent
C₂H₄	C=C	Double
C₂H₂	C≡C	Triple

19. MCQs — 30 Questions | बहुविकल्पीय प्रश्न

1. A covalent bond is formed by:
सहसंयोजक बंध बनता है:

A) Transfer of protons

B) Sharing of electrons

C) Transfer of neutrons

D) Loss of nucleus

Answer: B) Sharing of electrons

2. Carbon has how many valence electrons?

A) 2

B) 3

C) 4

D) 8

Answer: C) 4

3. Carbon generally completes its octet by:

A) Sharing electrons

B) Losing neutrons

C) Gaining protons

D) Losing the nucleus

Answer: A) Sharing electrons

4. How many electron pairs are shared in a single covalent bond?

A) 3

B) 2

C) 4

D) 1

Answer: D) 1

5. A double covalent bond contains:

A) One shared pair

B) Two shared pairs

C) Three shared pairs

D) Four shared pairs

Answer: B) Two shared pairs

6. A triple covalent bond contains:

A) One shared pair

B) Two shared pairs

C) Three shared pairs

D) Four shared pairs

Answer: C) Three shared pairs

7. Which molecule contains a double bond?

A) H₂

B) O₂

C) CH₄

D) Cl₂

Answer: B) O₂

8. Which molecule contains a triple bond?

A) N₂

B) O₂

C) H₂

D) CH₄

Answer: A) N₂

9. The bond in methane is:

A) Ionic

B) Metallic

C) Covalent

D) Coordinate only

Answer: C) Covalent

10. The formula of methane is:

A) CH₄

B) C₂H₆

C) C₂H₄

D) C₂H₂

Answer: A) CH₄

11. Which molecule has the structure C=C?

A) Ethane

B) Ethene

C) Ethyne

D) Methane

Answer: B) Ethene

12. Which molecule has the structure C≡C?

A) Ethane

B) Ethene

C) Ethyne

D) Methane

Answer: C) Ethyne

13. Which molecule has only single covalent bonds?

A) Ethane

B) Ethene

C) Ethyne

D) Nitrogen

Answer: A) Ethane

14. Electron-dot structures represent:

A) Neutrons

B) Valence electrons

C) Protons only

D) Atomic mass

Answer: B) Valence electrons

15. The stable electronic configuration generally involves:

A) 2 valence electrons for all atoms

B) 4 valence electrons

C) 8 valence electrons

D) 12 valence electrons

Answer: C) 8 valence electrons

16. Hydrogen follows the:

A) Octet rule only

B) Duplet rule

C) Decet rule

D) Zero-electron rule

Answer: B) Duplet rule

17. Which compound contains four C–H bonds?

A) CH₄

B) C₂H₆

C) C₂H₄

D) C₂H₂

Answer: A) CH₄

18. How many C–H bonds are present in methane?

A) 2

B) 3

C) 4

D) 5

Answer: C) 4

19. Ethane contains:

A) One C–C single bond

B) One C=C double bond

C) One C≡C triple bond

D) No C–C bond

Answer: A) One C–C single bond

20. Ethene contains:

A) C—C

B) C=C

C) C≡C

D) C⁴⁺

Answer: B) C=C

21. Ethyne contains:

A) C—C

B) C=C

C) C≡C

D) Ionic C–C

Answer: C) C≡C

22. Most covalent compounds are:

A) Good conductors of electricity

B) Poor conductors of electricity

C) Metals

D) Ionic solids

Answer: B) Poor conductors of electricity

23. Why do most covalent compounds not conduct electricity?

A) They contain no freely moving ions

B) They contain many protons

C) They are always metals

D) They contain neutrons only

Answer: A) They contain no freely moving ions

24. Which substance is a giant covalent structure?

A) NaCl

B) Diamond

C) CH₄

D) H₂

Answer: B) Diamond

25. Which generally has low melting and boiling points?

A) Many simple covalent compounds

B) Ionic compounds only

C) Metals only

D) Diamond only

Answer: A) Many simple covalent compounds

26. Which bond is formed by sharing three electron pairs?

A) Single

B) Double

C) Triple

D) Ionic

Answer: C) Triple

27. Which of the following is a covalent molecule?

A) CH₄

B) NaCl

C) KBr

D) MgO

Answer: A) CH₄

28. In carbon compounds, covalent bonds are formed mainly by:

A) Sharing of electrons

B) Sharing of protons

C) Transfer of neutrons

D) Nuclear fusion

Answer: A) Sharing of electrons

29. Which pair contains a double and a triple bond respectively?

A) Ethene and ethyne

B) Ethane and ethene

C) Methane and ethane

D) H₂ and Cl₂

Answer: A) Ethene and ethyne

30. The main reason carbon forms covalent bonds is:

A) It has four valence electrons

B) It has no electrons

C) It is a metal

D) It has eight shells

Answer: A) It has four valence electrons

20. Subjective Questions — 30 Questions | वर्णनात्मक प्रश्न

1 Mark 1. Define covalent bond.

A covalent bond is a bond formed by sharing of electron pairs between atoms.
हिन्दी: परमाणुओं के बीच इलेक्ट्रॉन युग्मों की साझेदारी से बनने वाला बंध सहसंयोजक बंध कहलाता है।

1 Mark 2. How many valence electrons does carbon have?

Carbon has 4 valence electrons.

1 Mark 3. How many electron pairs are shared in a double bond?

Two electron pairs.

1 Mark 4. Give one example of a molecule having a triple bond.

Nitrogen molecule (N₂) or ethyne (C₂H₂).

1 Mark 5. What is an electron-dot structure?

It is a representation of valence electrons of atoms using dots.

2 Marks 6. Why does carbon form covalent bonds?

Carbon has four valence electrons. Losing or gaining four electrons is difficult, so it achieves stability by sharing electrons.

2 Marks 7. What is meant by a single covalent bond?

A single covalent bond is formed when one pair of electrons is shared between two atoms. Example: H—H.

2 Marks 8. What is a double covalent bond?

A double covalent bond is formed by sharing two pairs of electrons. Example: O=O or C=C.

2 Marks 9. What is a triple covalent bond?

A triple covalent bond is formed by sharing three pairs of electrons. Example: N≡N or C≡C.

2 Marks 10. Why are most covalent compounds poor conductors of electricity?

Most covalent compounds do not contain freely moving ions or electrons. Therefore, they generally do not conduct electricity.

3 Marks 11. Explain the formation of H₂ using electron sharing.

Each hydrogen atom has one electron. The two hydrogen atoms share these electrons to form one shared pair.

H—H

Both hydrogen atoms achieve a stable duplet.

3 Marks 12. Explain the formation of O₂.

Each oxygen atom has six valence electrons and requires two more electrons. Two oxygen atoms therefore share two pairs of electrons and form a double bond.

O=O

3 Marks 13. Explain the formation of N₂.

Each nitrogen atom has five valence electrons and requires three more electrons. Two nitrogen atoms share three electron pairs.

N≡N

Thus a triple covalent bond is formed.

3 Marks 14. Explain the formation of methane using covalent bonding.

Carbon has four valence electrons and each hydrogen has one. Carbon shares one electron with each of four hydrogen atoms and forms four C–H covalent bonds.

CH₄

3 Marks 15. What information is provided by an electron-dot structure?

It shows valence electrons, shared electron pairs, number of covalent bonds and how atoms achieve stable electronic configurations.

4 Marks 16. Explain the formation of ethane (C₂H₆).

Two carbon atoms share one pair of electrons to form a C–C single bond. Each carbon then shares electrons with three hydrogen atoms, forming three C–H bonds.

CH₃—CH₃

4 Marks 17. Explain the formation of ethene (C₂H₄).

The two carbon atoms share two pairs of electrons, forming a C=C double bond. Each carbon forms two C–H bonds.

CH₂=CH₂

4 Marks 18. Explain the formation of ethyne (C₂H₂).

The two carbon atoms share three pairs of electrons, forming a C≡C triple bond. Each carbon also forms one C–H bond.

HC≡CH

4 Marks 19. Differentiate between single, double and triple covalent bonds.

Bond	Shared Pairs	Example
Single	1	H—H
Double	2	O=O
Triple	3	N≡N

4 Marks 20. Differentiate between covalent and ionic bonds.

Covalent Bond	Ionic Bond
Electrons are shared.	Electrons are transferred.
Usually between non-metals.	Usually between metal and non-metal.
Example: CH₄.	Example: NaCl.

5 Marks 21. Explain why carbon cannot form C⁴⁺ or C⁴⁻ ions easily.

Carbon has four valence electrons. Removing all four electrons requires a very large amount of energy. Gaining four electrons is also difficult because it would create a highly charged and unstable ion. Therefore carbon completes its octet mainly through electron sharing and forms covalent bonds.

5 Marks 22. Explain the electron-dot structure of methane.

Carbon has four valence electrons and each hydrogen has one. Carbon shares one electron with each of four hydrogen atoms. Four shared pairs are formed, producing four C–H covalent bonds.

    H
    |
H—C—H
    |
    H

5 Marks 23. Explain the electron-dot structure of oxygen molecule.

Each oxygen atom has six valence electrons and needs two more electrons. The two oxygen atoms share two electron pairs, resulting in a double covalent bond.

O=O

Each oxygen completes its octet.

5 Marks 24. Explain the electron-dot structure of nitrogen molecule.

Each nitrogen atom has five valence electrons and needs three more electrons. The two nitrogen atoms share three pairs of electrons and form a triple bond.

N≡N

Both nitrogen atoms achieve an octet.

5 Marks 25. State the important properties of covalent compounds.

Important properties include:
1. They are generally poor conductors of electricity.
2. Many have low melting and boiling points.
3. Many are insoluble or sparingly soluble in water.
4. Many are soluble in organic solvents.
5. They generally consist of molecules.
Exception: Giant covalent structures such as diamond have very high melting points.

6 Marks 26. Explain covalent bonding in carbon compounds in detail.

Carbon has electronic configuration 2,4 and four valence electrons. It does not easily lose or gain four electrons. Hence it shares electrons with other atoms.

Carbon forms four covalent bonds because of its tetravalency. It can also form C–C single, double and triple bonds. Examples include CH₄, C₂H₆, C₂H₄ and C₂H₂.

This ability to form strong covalent bonds contributes greatly to the diversity of carbon compounds.

6 Marks 27. Explain electron-dot structures of H₂, O₂ and N₂.

H₂: One pair of electrons is shared.

H—H

O₂: Two pairs of electrons are shared.

O=O

N₂: Three pairs of electrons are shared.

N≡N

Thus H₂ has a single bond, O₂ has a double bond and N₂ has a triple bond.

6 Marks 28. Explain the formation of ethane, ethene and ethyne.

Ethane:

CH₃—CH₃

One C–C single bond. Ethene:

CH₂=CH₂

One C=C double bond. Ethyne:

HC≡CH

One C≡C triple bond. The difference arises from the number of electron pairs shared between the two carbon atoms.

6 Marks 29. Explain octet and duplet rules with reference to covalent bonding.

The octet rule states that atoms tend to achieve eight electrons in their valence shell for stability. Covalent bonding allows atoms to achieve this by sharing electrons.

Hydrogen is an exception. It requires only two electrons to achieve a stable duplet. Therefore H₂ is formed by sharing one electron pair between two hydrogen atoms.

6 Marks 30. Explain why carbon compounds generally have covalent bonds and how electron-dot structures help in understanding them.

Carbon has four valence electrons. Neither losing nor gaining four electrons is energetically favourable. Therefore carbon shares electrons and forms covalent bonds.

Electron-dot structures represent valence electrons as dots and show shared electron pairs. They help determine the number and type of covalent bonds and show how atoms complete their stable electronic configurations.

For example:

CH₄ → Four C–H single bonds
C₂H₄ → One C=C double bond
C₂H₂ → One C≡C triple bond

21. Foundation + Competitive Quick Revision

🔥 Super Important Facts:

• Covalent bond = sharing of electron pairs.
• Carbon has 4 valence electrons.
• Carbon usually forms 4 covalent bonds.
• Single bond = 1 shared electron pair.
• Double bond = 2 shared electron pairs.
• Triple bond = 3 shared electron pairs.
• H₂ contains a single bond.
• O₂ contains a double bond.
• N₂ contains a triple bond.
• CH₄ contains four C–H covalent bonds.
• C₂H₆ contains a C–C single bond.
• C₂H₄ contains a C=C double bond.
• C₂H₂ contains a C≡C triple bond.
• Most simple covalent compounds are poor conductors of electricity.
• Diamond is a giant covalent structure.
• Hydrogen follows the duplet rule.

22. One-Line Revision | एक पंक्ति में पुनरावृत्ति

Covalent Bond = Electron Sharing → Stable Configuration → Molecule Formation.

हिन्दी:
सहसंयोजक बंध = इलेक्ट्रॉन साझेदारी → स्थिर इलेक्ट्रॉनिक विन्यास → अणु का निर्माण।