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।