Class XI Unit 3: - Classification of Elements and Periodicity in Properties,

Class XI Unit 3:

 Classification of Elements and Periodicity in Properties and the supplementary topics on s & p Block Elements,  competitive-level (JEE/NEET) 

Genesis & Modern Periodic Law

1. What is the physical basis of the Modern Periodic Law as proposed by Henry Moseley?
2. How does the Modern Periodic Law rectify the position of isotopes which was a drawback in Mendeleev’s table?
3. Why did the Law of Octaves fail to classify elements with higher atomic weights?
4. In the present form of the Periodic Table, the period number corresponds to which quantum number of the elements?
5. What is the significance of the atomic number being the fundamental property for classification instead of atomic mass?

Which element has the highest Electronegativity in the periodic table?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

🏆 Fluorine (F)

Fluorine (F) is the most electronegative element in the periodic table.

Its electronegativity on the Pauling scale is approximately 3.98, the highest value of all elements.

🔍 Why does Fluorine have the highest electronegativity?

• Fluorine has a very small atomic radius.
• It has a relatively high effective nuclear charge.
• Its valence shell is close to the nucleus.
• Therefore, it strongly attracts the shared electron pair in a chemical bond.

Small Atomic Radius + High Effective Nuclear Charge
↓
Strong Attraction for Shared Electrons
↓
Highest Electronegativity

📊 Important Comparison

Element	Approx. Pauling Electronegativity
F	3.98
O	3.44
Cl	3.16
N	3.04

✅ Final Answer

Fluorine (F)

Fluorine has the highest electronegativity in the periodic table, with a Pauling electronegativity of approximately 3.98.

20 MCQs with Answers

1. Which element has the highest electronegativity?

A) Oxygen

B) Chlorine

C) Fluorine

D) Nitrogen

✅ Answer

C) Fluorine

---

2. The electronegativity of fluorine on the Pauling scale is approximately:

A) 2.20

B) 3.00

C) 3.44

D) 3.98

✅ Answer

D) 3.98

---

3. Fluorine belongs to which group?

A) 1

B) 15

C) 17

D) 18

✅ Answer

C) 17

---

4. Fluorine has high electronegativity mainly because of:

A) Large atomic radius

B) Small atomic radius

C) Low nuclear charge

D) Many electron shells

✅ Answer

B) Small atomic radius

---

5. Which element is more electronegative than chlorine?

A) Fluorine

B) Bromine

C) Iodine

D) Sulfur

✅ Answer

A) Fluorine

---

6. Electronegativity generally increases:

A) Down a group

B) From right to left

C) From left to right across a period

D) Randomly

✅ Answer

C

---

7. Fluorine is a member of the:

A) Alkali metals

B) Alkaline earth metals

C) Halogens

D) Noble gases

✅ Answer

C) Halogens

---

8. Which property of fluorine contributes to its high electronegativity?

A) Small atomic size

B) Large number of shells

C) Low effective nuclear charge

D) Metallic character

✅ Answer

A) Small atomic size

---

9. Which has the greatest attraction for a shared electron pair?

A) Li

B) C

C) O

D) F

✅ Answer

D) F

---

10. The highest electronegativity is found toward the:

A) Bottom-left

B) Top-right

C) Centre

D) Bottom-centre

✅ Answer

B) Top-right

---

11. Which is the most electronegative halogen?

A) Cl

B) Br

C) I

D) F

✅ Answer

D) F

---

12. Which element has electronegativity approximately 3.44?

A) F

B) O

C) N

D) Cl

✅ Answer

B) O

---

13. The small atomic radius of fluorine results in:

A) Weak attraction for bonding electrons

B) Strong attraction for bonding electrons

C) Low electronegativity

D) High metallic character

✅ Answer

B

---

14. Fluorine has how many valence electrons?

A) 5

B) 6

C) 7

D) 8

✅ Answer

C) 7

---

15. Fluorine belongs to which block?

A) s-block

B) p-block

C) d-block

D) f-block

✅ Answer

B) p-block

---

16. Which element has higher electronegativity?

A) F

B) Cl

C) Both equal

D) I

✅ Answer

A) F

---

17. Electronegativity measures the ability of an atom to:

A) Attract shared electrons

B) Lose neutrons

C) Attract protons

D) Lose its nucleus

✅ Answer

A

---

18. Which element has the strongest non-metallic character among the following?

A) Na

B) Mg

C) Cl

D) K

✅ Answer

C) Cl

---

19. Fluorine's high electronegativity is associated with:

A) High effective nuclear charge

B) Very large atomic radius

C) Many occupied shells

D) Low nuclear attraction

✅ Answer

A

---

20. The correct statement is:

A) Fluorine has the lowest electronegativity

B) Fluorine has the highest electronegativity

C) Chlorine is more electronegative than fluorine

D) Electronegativity is absent in fluorine

✅ Answer

B) Fluorine has the highest electronegativity

Q. Which element has the highest electronegativity in the periodic table?

Solution: Fluorine (F) has the highest electronegativity in the periodic table. Its Pauling electronegativity is approximately 3.98.

Q. Why does fluorine have the highest electronegativity?

Solution:

• Fluorine has a very small atomic radius.
• It has a high effective nuclear charge.
• Therefore, it strongly attracts the shared electron pair towards itself.

Q. Explain the reasons for the highest electronegativity of fluorine.

Solution: Fluorine has the smallest atomic radius among the halogens and a high effective nuclear charge. Its valence electrons are close to the nucleus. Hence, the attraction between the nucleus and the shared pair of bonding electrons is very strong. Therefore, fluorine has the highest electronegativity, approximately 3.98 on the Pauling scale.

Q. Discuss the position of fluorine in the periodic trend of electronegativity.

Solution:

Electronegativity generally increases from left to right across a period and decreases down a group. Fluorine is located in Group 17 and Period 2. It has a very small atomic size and high effective nuclear charge.

Because its valence shell is very close to the nucleus, fluorine strongly attracts the shared pair of electrons in a covalent bond. Hence, it has the highest electronegativity of all elements.

Fluorine (F) → Highest Electronegativity → ≈ 3.98 (Pauling scale)

Q. Explain in detail why fluorine has the highest electronegativity in the periodic table.

1. Small Atomic Size

Fluorine is a second-period element and has only two occupied electron shells. Its atomic radius is therefore very small.

2. High Effective Nuclear Charge

Fluorine has nine protons, while its inner-shell electrons provide relatively limited shielding. Thus its valence electrons experience a strong effective nuclear attraction.

3. Strong Attraction for Bonding Electrons

Because the valence shell is close to the nucleus, fluorine strongly attracts the shared electron pair in a covalent bond.

4. Periodic Trend

Electronegativity generally increases across a period and decreases down a group. Fluorine is at the upper-right side of the periodic table (excluding noble gases), where electronegativity is highest.

Small Atomic Radius
+
High Effective Nuclear Charge
↓
Strong Attraction for Shared Electrons
↓
Highest Electronegativity: F

Final Answer:
Fluorine (F) is the most electronegative element in the periodic table. Its Pauling electronegativity is approximately 3.98.

🎯 Quick Revision

Highest Electronegativity: Fluorine (F)
Group: 17
Period: 2
Block: p-block
Pauling value: ≈ 3.98
Main reason: Small atomic radius + high effective nuclear charge

What is the relation between Electronegativity and Non-metallic character?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

Electronegativity and non-metallic character are directly related. An element having higher electronegativity generally shows a stronger non-metallic character.

Electronegativity ↑   →   Non-metallic Character ↑

Non-metals have a strong tendency to attract electrons towards themselves. Therefore, elements with high electronegativity are generally more non-metallic in nature.

🔍 Periodic Trend

Across a period:

Electronegativity generally increases from left to right, and therefore non-metallic character also increases.

Metallic Character ↓   |   Non-metallic Character ↑

Left → Right

Down a group:

Electronegativity generally decreases down a group, so non-metallic character decreases and metallic character increases.

📊 Example

In the second period:

Li → Be → B → C → N → O → F

Non-metallic character generally ↑
Electronegativity generally ↑

Fluorine has the highest electronegativity and is strongly non-metallic, whereas lithium is much more metallic and has much lower electronegativity.

✅ Final Answer

Higher electronegativity indicates a greater tendency to attract electrons and is generally associated with stronger non-metallic character.

Electronegativity ↑ → Non-metallic Character ↑

20 MCQs with Answers

1. Electronegativity and non-metallic character are generally:

A) Directly related

B) Inversely related

C) Unrelated

D) Always equal

✅ Answer

A) Directly related

---

2. An element with high electronegativity generally has:

A) High metallic character

B) High non-metallic character

C) Zero non-metallic character

D) No chemical activity

✅ Answer

B) High non-metallic character

---

3. Across a period, non-metallic character generally:

A) Decreases

B) Increases

C) Remains constant

D) Becomes zero

✅ Answer

B) Increases

---

4. Across a period, electronegativity generally:

A) Increases

B) Decreases

C) Remains constant

D) Has no trend

✅ Answer

A) Increases

---

5. Which element is strongly non-metallic?

A) Na

B) Mg

C) F

D) K

✅ Answer

C) F

---

6. Fluorine has a strong non-metallic character because it has:

A) Low electronegativity

B) High electronegativity

C) Large atomic size

D) Low nuclear charge

✅ Answer

B) High electronegativity

---

7. Down a group, non-metallic character generally:

A) Increases

B) Decreases

C) Remains constant

D) Doubles

✅ Answer

B) Decreases

---

8. Down a group, metallic character generally:

A) Increases

B) Decreases

C) Remains zero

D) Does not change

✅ Answer

A) Increases

---

9. Which property is generally associated with non-metals?

A) Low electronegativity

B) High electronegativity

C) Very large atomic size only

D) Easy loss of electrons

✅ Answer

B) High electronegativity

---

10. Which has greater non-metallic character?

A) Li

B) F

C) Na

D) K

✅ Answer

B) F

---

11. The tendency of an atom to attract shared electrons is called:

A) Ionization enthalpy

B) Electronegativity

C) Electron affinity

D) Atomic radius

✅ Answer

B) Electronegativity

---

12. Which trend is correct across a period?

A) Metallic character ↑, non-metallic character ↓

B) Metallic character ↓, non-metallic character ↑

C) Both decrease

D) Both remain constant

✅ Answer

B

---

13. High electronegativity means a stronger tendency to:

A) Lose shared electrons

B) Attract shared electrons

C) Lose protons

D) Lose neutrons

✅ Answer

B) Attract shared electrons

---

14. Which element is more non-metallic?

A) Na

B) Cl

C) Mg

D) Al

✅ Answer

B) Cl

---

15. The most electronegative element is:

A) O

B) Cl

C) F

D) N

✅ Answer

C) F

---

16. Non-metallic character is generally maximum toward the:

A) Bottom-left of the periodic table

B) Top-right of the periodic table

C) Centre only

D) Bottom-right only

✅ Answer

B) Top-right

---

17. Metallic character and electronegativity generally show:

A) Direct relationship

B) Opposite trends

C) No relationship

D) Identical values

✅ Answer

B) Opposite trends

---

18. Which element is expected to have greater electronegativity?

A) Na

B) Cl

C) K

D) Rb

✅ Answer

B) Cl

---

19. Greater electronegativity generally indicates:

A) Greater non-metallic nature

B) Greater metallic nature

C) Lower electron attraction

D) Larger atomic radius necessarily

✅ Answer

A) Greater non-metallic nature

---

20. Which statement is correct?

A) Electronegativity increases as non-metallic character decreases

B) High electronegativity is generally associated with high non-metallic character

C) Metals are always more electronegative than non-metals

D) Electronegativity has no periodic trend

✅ Answer

B

Q. State the relationship between electronegativity and non-metallic character.

Solution: Electronegativity and non-metallic character are generally directly related. As electronegativity increases, the tendency to attract electrons increases, so non-metallic character also increases.

Electronegativity ↑ → Non-metallic Character ↑

Q. Explain the relationship between electronegativity and non-metallic character.

Solution:

• Non-metals have a strong tendency to attract electrons.
• Electronegativity measures the attraction for a shared pair of electrons.
• Therefore, higher electronegativity generally corresponds to greater non-metallic character.

Q. Explain the periodic variation of electronegativity and non-metallic character.

Solution: Across a period, effective nuclear charge increases and atomic size decreases. Therefore, electronegativity increases and non-metallic character also increases. Down a group, atomic size and shielding effect increase, causing electronegativity and non-metallic character to decrease.

Across a period: EN ↑ → Non-metallic character ↑

Down a group: EN ↓ → Non-metallic character ↓

Q. Discuss the relationship between electronegativity and non-metallic character with examples.

Solution:

Electronegativity is the tendency of an atom in a molecule to attract the shared electron pair towards itself. Non-metallic character represents the tendency of an element to accept or attract electrons.

Thus, both properties are closely related. An element with high electronegativity generally has strong non-metallic character.

For example, fluorine has the highest electronegativity and is highly non-metallic. Across a period, both electronegativity and non-metallic character generally increase.

Electronegativity ↑ → Non-metallic Character ↑

Q. Explain in detail the relationship between electronegativity and non-metallic character and discuss their periodic trends.

1. Electronegativity

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

2. Non-metallic Character

Non-metallic character refers to the tendency of an element to attract or gain electrons and to show properties characteristic of non-metals.

3. Relationship

Both properties depend strongly on the ability of an atom to attract electrons. Hence, they generally vary in the same direction.

Electronegativity ↑
↓
Electron-attracting tendency ↑
↓
Non-metallic Character ↑

4. Across a Period

From left to right, effective nuclear charge increases and atomic size decreases. Therefore, electronegativity and non-metallic character generally increase.

5. Down a Group

Down a group, atomic size and shielding effect increase. The attraction for electrons decreases. Hence electronegativity and non-metallic character generally decrease.

Across Period: EN ↑ → Non-metallic Character ↑

Down Group: EN ↓ → Non-metallic Character ↓

Key Point:
Higher electronegativity is generally associated with stronger non-metallic character.

🎯 Quick Revision

Relation: Direct relationship
Across period: Electronegativity ↑, Non-metallic character ↑
Down group: Electronegativity ↓, Non-metallic character ↓
Most electronegative: Fluorine (F)
General location of strong non-metallic character: Upper-right region

How does Electronegativity change across a period from Li to F?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

Across the second period, from Li → F, electronegativity generally increases from left to right.

Li < Be < B < C < N < O < F

Fluorine (F) has the highest electronegativity among these elements.

🔍 Why does electronegativity increase?

• Effective nuclear charge increases from Li to F.
• The number of shells remains the same throughout the second period.
• Atomic radius generally decreases.
• Therefore, the nucleus attracts the shared electron pair more strongly.
• Hence, electronegativity increases from Li to F.

Effective Nuclear Charge ↑
↓
Atomic Size ↓
↓
Attraction for Shared Electrons ↑
↓
Electronegativity ↑

📊 Approximate Pauling Electronegativity

Element	Electronegativity
Li	0.98
Be	1.57
B	2.04
C	2.55
N	3.04
O	3.44
F	3.98

✅ Final Answer

Electronegativity increases from Li to F.

Li < Be < B < C < N < O < F

This is mainly due to increasing effective nuclear charge and decreasing atomic radius across the period.

20 MCQs with Answers

1. Electronegativity from Li to F generally:

A) Decreases

B) Increases

C) Remains constant

D) First decreases then increases

✅ Answer

B) Increases

---

2. Which element has the highest electronegativity among Li, Be, B, C, N, O and F?

A) Li

B) C

C) O

D) F

✅ Answer

D) F

---

3. Which element has the lowest electronegativity?

A) Li

B) B

C) N

D) F

✅ Answer

A) Li

---

4. The increase in electronegativity across a period is mainly due to:

A) Decrease in nuclear charge

B) Increase in effective nuclear charge

C) Increase in shells

D) Increase in atomic size

✅ Answer

B) Increase in effective nuclear charge

---

5. From Li to F, the number of electron shells:

A) Increases

B) Decreases

C) Remains the same

D) Becomes zero

✅ Answer

C) Remains the same

---

6. Atomic radius across the second period generally:

A) Increases

B) Decreases

C) Remains constant

D) Doubles

✅ Answer

B) Decreases

---

7. Which has greater electronegativity?

A) Li

B) F

C) Both equal

D) Cannot be determined

✅ Answer

B) F

---

8. Across a period, effective nuclear charge generally:

A) Increases

B) Decreases

C) Remains constant

D) Becomes zero

✅ Answer

A) Increases

---

9. Which element is most electronegative?

A) C

B) N

C) O

D) F

✅ Answer

D) F

---

10. Electronegativity represents the tendency to attract:

A) Neutrons

B) Protons

C) Shared electron pair

D) Nucleus

✅ Answer

C) Shared electron pair

---

11. The correct increasing order is:

A) F < O < N < C

B) C < N < O < F

C) N < C < F < O

D) O < F < C < N

✅ Answer

B) C < N < O < F

---

12. Which has the smallest atomic size among Li to F?

A) Li

B) C

C) O

D) F

✅ Answer

D) F

---

13. Electronegativity generally increases from:

A) Right to left

B) Left to right

C) Bottom to top only

D) Randomly

✅ Answer

B) Left to right

---

14. Which factor opposes the attraction of the nucleus for valence electrons?

A) Shielding effect

B) Nuclear charge

C) Effective nuclear charge

D) Proton number

✅ Answer

A) Shielding effect

---

15. Which has higher electronegativity?

A) B

B) C

C) Both equal

D) Cannot be compared

✅ Answer

B) C

---

16. Fluorine has high electronegativity mainly because of its:

A) Large atomic radius

B) Small atomic radius and high effective nuclear charge

C) Large number of shells

D) Metallic character

✅ Answer

B

---

17. Which sequence represents decreasing electronegativity?

A) Li > Be > B > C > N > O > F

B) F > O > N > C > B > Be > Li

C) Li > F > O > N

D) F > Li > O > C

✅ Answer

B

---

18. Across a period, nuclear charge:

A) Increases

B) Decreases

C) Remains constant

D) Becomes negative

✅ Answer

A) Increases

---

19. Electronegativity of Li is lower than F because Li has:

A) Larger atomic size

B) Smaller atomic size

C) Greater effective nuclear charge

D) More protons than F

✅ Answer

A) Larger atomic size

---

20. The overall trend across Li → F is:

A) Electronegativity ↓

B) Electronegativity ↑

C) No trend

D) Electronegativity becomes zero

✅ Answer

B) Electronegativity ↑

Q. How does electronegativity change from Li to F?

Solution: Electronegativity generally increases from Li to F because effective nuclear charge increases and atomic radius decreases.

Li < Be < B < C < N < O < F

Q. Give reasons for the increase in electronegativity from Li to F.

Solution:

• All elements lie in the same period, so the number of shells remains the same.
• Nuclear charge increases from Li to F.
• Effective nuclear charge increases and atomic radius decreases.
• Therefore, attraction for shared electrons increases.

Q. Explain the variation of electronegativity across the second period from Li to F.

Solution: Across the second period, the number of electron shells remains constant while the number of protons increases. Shielding does not increase substantially because electrons are added to the same principal shell. Thus effective nuclear charge increases, atomic size decreases, and the nucleus attracts shared electrons more strongly.

Li < Be < B < C < N < O < F

Q. Explain why electronegativity increases from Li to F.

Solution:

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

From Li to F, the nuclear charge increases progressively. Since all these elements belong to the second period, the added electrons enter the same principal shell. Therefore, effective nuclear charge increases and atomic radius decreases.

The smaller atomic radius brings the shared electron pair closer to the nucleus, while the higher effective nuclear charge increases attraction. Hence electronegativity increases.

Li < Be < B < C < N < O < F

Q. Explain in detail the periodic trend of electronegativity from Li to F.

1. Same Period

Li, Be, B, C, N, O and F all belong to the second period. Therefore, their valence electrons are present in the same principal shell.

2. Increase in Nuclear Charge

As we move from Li to F, the number of protons increases. Thus the positive charge of the nucleus increases.

3. Effective Nuclear Charge

The additional electrons enter the same shell, so the increase in shielding is relatively small. Consequently, effective nuclear charge experienced by the valence electrons increases.

4. Decrease in Atomic Radius

Increasing effective nuclear charge pulls the electron cloud closer to the nucleus. Hence atomic radius decreases from Li to F.

5. Increase in Electronegativity

The smaller atomic size and greater effective nuclear charge make the atom more effective at attracting the shared pair of electrons in a chemical bond.

Nuclear Charge ↑
↓
Effective Nuclear Charge ↑
↓
Atomic Radius ↓
↓
Attraction for Shared Electrons ↑
↓
Electronegativity ↑

Final Order:

Li < Be < B < C < N < O < F

🎯 Quick Revision

Across period: Electronegativity ↑
Atomic size: ↓
Effective nuclear charge: ↑
Number of shells: Same
Highest in Li → F: F
Order: Li < Be < B < C < N < O < F

Arrange F,Cl,Br,I in order of decreasing Electronegativity.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Solution

All four elements belong to Group 17 (Halogens) of the periodic table.

The electronegativity of elements generally decreases down a group because atomic size and shielding effect increase.

F > Cl > Br > I

🔍 Reason

• Down the group, the number of electron shells increases.
• Atomic size increases.
• Shielding effect increases.
• The attraction between the nucleus and shared electrons decreases.
• Therefore, electronegativity decreases down the group.

📊 Electronegativity Values (Pauling Scale)

Element	Electronegativity
F	3.98
Cl	3.16
Br	2.96
I	2.66

✅ Final Answer

Decreasing order of electronegativity:

F > Cl > Br > I

20 MCQs with Answers

1. Which halogen has the highest electronegativity?

A) Cl

B) Br

C) F

D) I

✅ Answer

C) F

---

2. The correct decreasing order of electronegativity is:

A) I > Br > Cl > F

B) F > Cl > Br > I

C) Cl > F > I > Br

D) Br > I > Cl > F

✅ Answer

B) F > Cl > Br > I

---

3. Electronegativity down Group 17 generally:

A) Increases

B) Decreases

C) Remains constant

D) First increases then decreases

✅ Answer

B) Decreases

---

4. Which element has the smallest electronegativity among F, Cl, Br and I?

A) F

B) Cl

C) Br

D) I

✅ Answer

D) I

---

5. Electronegativity is the tendency to attract:

A) Protons

B) Neutrons

C) Shared electrons

D) Nuclei

✅ Answer

C) Shared electrons

---

6. The most electronegative element is:

A) Oxygen

B) Fluorine

C) Chlorine

D) Nitrogen

✅ Answer

B) Fluorine

---

7. Which factor increases down a group?

A) Electronegativity

B) Atomic size

C) Nuclear attraction on valence electrons

D) Effective nuclear charge across the period

✅ Answer

B) Atomic size

---

8. The shielding effect down a group generally:

A) Decreases

B) Increases

C) Becomes zero

D) Remains unchanged

✅ Answer

B) Increases

---

9. Which has greater electronegativity?

A) F

B) I

C) Both equal

D) Cannot be compared

✅ Answer

A) F

---

10. Chlorine is more electronegative than bromine because chlorine has:

A) Larger atomic size

B) Smaller atomic size

C) More shells

D) More shielding

✅ Answer

B) Smaller atomic size

---

11. Electronegativity is generally measured using:

A) Kelvin scale

B) Celsius scale

C) Pauling scale

D) pH scale

✅ Answer

C) Pauling scale

---

12. Which order represents increasing electronegativity?

A) F > Cl > Br > I

B) I < Br < Cl < F

C) Both A and B

D) I > Br > Cl > F

✅ Answer

C) Both A and B

---

13. F, Cl, Br and I belong to:

A) Group 1

B) Group 2

C) Group 17

D) Group 18

✅ Answer

C) Group 17

---

14. Which halogen has the largest atomic radius?

A) F

B) Cl

C) Br

D) I

✅ Answer

D) I

---

15. Increase in atomic size generally causes electronegativity to:

A) Increase

B) Decrease

C) Become infinite

D) Remain exactly constant

✅ Answer

B) Decrease

---

16. Which has the highest attraction for a shared electron pair?

A) F

B) Cl

C) Br

D) I

✅ Answer

A) F

---

17. Electronegativity generally increases:

A) Down a group

B) From left to right across a period

C) From top to bottom only

D) Randomly

✅ Answer

B

---

18. Which sequence is correct for electronegativity?

A) I < Br < Cl < F

B) F < Cl < Br < I

C) Br < I < F < Cl

D) Cl < I < Br < F

✅ Answer

A) I < Br < Cl < F

---

19. The decrease in electronegativity down Group 17 is mainly due to:

A) Decrease in atomic size

B) Increase in atomic size and shielding

C) Decrease in shells

D) Decrease in electrons

✅ Answer

B

---

20. The correct statement is:

A) I is more electronegative than F

B) Br is more electronegative than Cl

C) F is the most electronegative halogen

D) Electronegativity increases down Group 17

✅ Answer

C) F is the most electronegative halogen

Q. Arrange F, Cl, Br and I in decreasing order of electronegativity.

Solution: Electronegativity decreases down Group 17 due to increase in atomic size and shielding effect.

F > Cl > Br > I

Q. Explain the trend of electronegativity among F, Cl, Br and I.

Solution:

• F, Cl, Br and I belong to Group 17.
• Atomic size and shielding effect increase down the group.
• Therefore, attraction for shared electrons decreases.

Decreasing order: F > Cl > Br > I

Q. Give reasons for the decreasing order of electronegativity of F, Cl, Br and I.

Solution:

As we move from F to I down Group 17, a new electron shell is added at each step. Consequently, atomic radius and shielding effect increase. The shared electron pair becomes farther from the nucleus and experiences less effective attraction. Hence electronegativity decreases.

F > Cl > Br > I

Q. Explain the variation of electronegativity down Group 17 with suitable examples.

Solution:

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

F, Cl, Br and I are members of Group 17. Down the group, the number of electron shells increases. This increases atomic size and shielding effect. As a result, the nucleus attracts the shared electron pair less strongly.

Therefore, electronegativity decreases down the group:

F > Cl > Br > I

Q. Explain in detail the trend in electronegativity of F, Cl, Br and I.

1. Position in the Periodic Table

F, Cl, Br and I are halogens and belong to Group 17.

2. Downward Change in Atomic Size

As we move down the group, new electron shells are added. Therefore, the atomic radius increases from F to I.

3. Increase in Shielding Effect

The number of inner-shell electrons increases down the group. These electrons shield the valence electrons from the attraction of the nucleus.

4. Decrease in Attraction

Because the shared electron pair is farther from the nucleus and more strongly shielded, the attraction for the shared electrons decreases.

Atomic Size ↑ + Shielding Effect ↑
↓
Nuclear Attraction for Shared Electrons ↓
↓
Electronegativity ↓

5. Final Order

F > Cl > Br > I

Decreasing order of Electronegativity

🎯 Quick Revision

Group: 17 (Halogens)
Trend: Electronegativity decreases down the group
Highest: F
Lowest: I
Order: F > Cl > Br > I

Who proposed the Electronegativity scale commonly used in Chemistry?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Definition of Electronegativity

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

Electronegativity = Attraction for shared electrons in a chemical bond

It is a relative, dimensionless property and is commonly expressed using the Pauling scale.

⚛️ Electron Gain Enthalpy

Electron Gain Enthalpy (EGE) is the enthalpy change that occurs when an isolated gaseous atom gains an electron to form a gaseous negative ion.

X(g) + e⁻ → X⁻(g)

It is an energy-related quantity and is generally expressed in kJ mol⁻¹.

🔍 Difference Between Electronegativity and EGE

Electronegativity	Electron Gain Enthalpy
Tendency of an atom to attract shared electrons in a chemical bond.	Energy change when an isolated gaseous atom gains an electron.
Applies to an atom in a chemical bond.	Applies to an isolated gaseous atom.
It is a relative and dimensionless quantity.	It is an enthalpy/energy change.
Usually expressed on scales such as the Pauling scale.	Expressed in kJ mol⁻¹.

✅ Final Answer

Electronegativity is the tendency of an atom in a chemical bond to attract the shared electron pair towards itself.

Electron Gain Enthalpy is the enthalpy change when an isolated gaseous atom gains an electron.

The main difference is that electronegativity describes the attraction for shared electrons in a bond, whereas EGE describes the energy change associated with gaining an electron by an isolated gaseous atom.

20 MCQs with Answers

1. Electronegativity is the tendency of an atom to:

A) Lose neutrons

B) Attract shared electrons

C) Lose protons

D) Emit radiation

✅ Answer

B) Attract shared electrons

---

2. Electronegativity is associated with:

A) Isolated atom only

B) Atom in a chemical bond

C) Nucleus only

D) Free neutron

✅ Answer

B) Atom in a chemical bond

---

3. Electronegativity is a:

A) Dimensionless quantity

B) Quantity measured in kg

C) Quantity measured in litre

D) Quantity measured in metre

✅ Answer

A) Dimensionless quantity

---

4. The Pauling scale is used to measure:

A) Atomic mass

B) Ionization energy

C) Electronegativity

D) Atomic radius

✅ Answer

C) Electronegativity

---

5. Electron Gain Enthalpy involves:

A) Loss of an electron

B) Gain of an electron

C) Loss of a proton

D) Gain of a neutron

✅ Answer

B) Gain of an electron

---

6. EGE is generally expressed in:

A) kJ mol⁻¹

B) metre

C) kg

D) litre

✅ Answer

A) kJ mol⁻¹

---

7. EGE is defined for:

A) An isolated gaseous atom

B) A molecule only

C) A solid only

D) A liquid only

✅ Answer

A) An isolated gaseous atom

---

8. Which property is relative and dimensionless?

A) EGE

B) Electronegativity

C) Enthalpy

D) Ionization enthalpy

✅ Answer

B) Electronegativity

---

9. Which quantity represents an energy change?

A) Electronegativity

B) Electron Gain Enthalpy

C) Atomic number

D) Electronegativity scale

✅ Answer

B) Electron Gain Enthalpy

---

10. In electronegativity, the electrons being attracted are:

A) Core electrons

B) Shared/bonding electrons

C) Nuclear electrons

D) Neutrons

✅ Answer

B) Shared/bonding electrons

---

11. Which element has the highest electronegativity?

A) F

B) Cl

C) O

D) N

✅ Answer

A) Fluorine

---

12. Electronegativity generally increases:

A) Down a group

B) From left to right across a period

C) From right to left only

D) Randomly

✅ Answer

B

---

13. Electron gain enthalpy is concerned with:

A) Attraction of shared electrons

B) Energy change on electron addition

C) Bond length only

D) Atomic mass only

✅ Answer

B

---

14. Which statement is correct?

A) Electronegativity has units of kJ mol⁻¹

B) EGE is dimensionless

C) Electronegativity is dimensionless

D) Both are identical quantities

✅ Answer

C

---

15. The process represented by X(g) + e⁻ → X⁻(g) is related to:

A) Electronegativity

B) Electron Gain Enthalpy

C) Atomic radius

D) Metallic character

✅ Answer

B

---

16. Electronegativity is mainly useful in understanding:

A) Bond polarity

B) Nuclear mass

C) Radioactive decay only

D) Atomic mass number

✅ Answer

A) Bond polarity

---

17. A highly electronegative atom strongly attracts:

A) Shared electron pair

B) Neutrons

C) Protons from nucleus

D) Atomic nuclei only

✅ Answer

A

---

18. Which is NOT a difference between electronegativity and EGE?

A) Electronegativity is dimensionless

B) EGE is an energy change

C) Electronegativity concerns shared electrons

D) Both have exactly the same definition

✅ Answer

D

---

19. EGE can be positive or negative depending on:

A) Energy change accompanying electron addition

B) Atomic colour

C) Melting point only

D) Density only

✅ Answer

A

---

20. Which pair is correctly matched?

A) Electronegativity – kJ mol⁻¹

B) EGE – Pauling scale

C) Electronegativity – attraction for shared electrons

D) EGE – attraction for shared electrons

✅ Answer

C

Q. Define electronegativity and electron gain enthalpy.

Solution:

Electronegativity: The tendency of an atom in a chemical bond to attract the shared electron pair towards itself.

Electron Gain Enthalpy: The enthalpy change when an isolated gaseous atom gains an electron to form a negative ion.

Q. Differentiate between electronegativity and electron gain enthalpy.

Solution:

• Electronegativity is the tendency to attract shared electrons in a chemical bond.
• Electron gain enthalpy is the energy change when an isolated gaseous atom gains an electron.
• Electronegativity is dimensionless, whereas EGE is expressed in kJ mol⁻¹.

Q. Explain the difference between electronegativity and electron gain enthalpy with suitable points.

Solution:

Basis	Electronegativity	Electron Gain Enthalpy
Meaning	Attraction for shared electrons	Energy change on gaining electron
Atom	Atom in a chemical bond	Isolated gaseous atom
Nature	Relative property	Thermodynamic quantity
Unit	Dimensionless	kJ mol⁻¹

Q. Define electronegativity. Explain how it differs from electron gain enthalpy.

Solution:

Electronegativity is the tendency of an atom in a molecule to attract the shared pair of electrons towards itself. It is a relative and dimensionless property.

Electron gain enthalpy is the enthalpy change associated with the addition of an electron to an isolated gaseous atom.

Electronegativity
Chemical bond → Shared electrons → Relative attraction

EGE
Isolated gaseous atom → Electron added → Energy change

Thus, although both concepts are related to the tendency of atoms to attract electrons, they are not the same quantity.

Electronegativity describes electron attraction in a bond, whereas EGE describes the energy change on electron addition to an isolated gaseous atom.

Q. Define electronegativity and electron gain enthalpy. Compare their nature, conditions and significance.

1. Electronegativity

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

It is a relative and dimensionless quantity. The Pauling scale is commonly used to compare electronegativities of elements.

2. Electron Gain Enthalpy

Electron gain enthalpy is the enthalpy change when an isolated gaseous atom accepts an electron to form a gaseous anion.

X(g) + e⁻ → X⁻(g)

It is an energy-related quantity and is expressed in kJ mol⁻¹. It may be negative when energy is released or positive when energy is absorbed.

3. Major Differences

Point	Electronegativity	EGE
Definition	Attraction for shared electron pair	Energy change on electron gain
Condition	Atom in chemical bond	Isolated gaseous atom
Nature	Relative property	Thermodynamic quantity
Unit	No unit	kJ mol⁻¹
Use	Helps explain bond polarity	Shows energetics of electron addition

Final Conclusion:

Electronegativity and electron gain enthalpy are related but different concepts. Electronegativity is the relative tendency of an atom in a chemical bond to attract shared electrons, while electron gain enthalpy is the actual enthalpy change associated with adding an electron to an isolated gaseous atom.

🎯 Quick Revision

Electronegativity: Attraction for shared electrons
Condition: Atom in chemical bond
Nature: Relative & dimensionless
EGE: Energy change on electron gain
Condition: Isolated gaseous atom
Unit: kJ mol⁻¹

Define Electronegativity and how it differs from Electron Gain Enthalpy.

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Definition of Electronegativity

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

Electronegativity = Attraction for shared electrons in a chemical bond

It is a relative, dimensionless property and is commonly expressed using the Pauling scale.

⚛️ Electron Gain Enthalpy

Electron Gain Enthalpy (EGE) is the enthalpy change that occurs when an isolated gaseous atom gains an electron to form a gaseous negative ion.

X(g) + e⁻ → X⁻(g)

It is an energy-related quantity and is generally expressed in kJ mol⁻¹.

🔍 Difference Between Electronegativity and EGE

Electronegativity	Electron Gain Enthalpy
Tendency of an atom to attract shared electrons in a chemical bond.	Energy change when an isolated gaseous atom gains an electron.
Applies to an atom in a chemical bond.	Applies to an isolated gaseous atom.
It is a relative and dimensionless quantity.	It is an enthalpy/energy change.
Usually expressed on scales such as the Pauling scale.	Expressed in kJ mol⁻¹.

✅ Final Answer

Electronegativity is the tendency of an atom in a chemical bond to attract the shared electron pair towards itself.

Electron Gain Enthalpy is the enthalpy change when an isolated gaseous atom gains an electron.

The main difference is that electronegativity describes the attraction for shared electrons in a bond, whereas EGE describes the energy change associated with gaining an electron by an isolated gaseous atom.

20 MCQs with Answers

1. Electronegativity is the tendency of an atom to:

A) Lose neutrons

B) Attract shared electrons

C) Lose protons

D) Emit radiation

✅ Answer

B) Attract shared electrons

---

2. Electronegativity is associated with:

A) Isolated atom only

B) Atom in a chemical bond

C) Nucleus only

D) Free neutron

✅ Answer

B) Atom in a chemical bond

---

3. Electronegativity is a:

A) Dimensionless quantity

B) Quantity measured in kg

C) Quantity measured in litre

D) Quantity measured in metre

✅ Answer

A) Dimensionless quantity

---

4. The Pauling scale is used to measure:

A) Atomic mass

B) Ionization energy

C) Electronegativity

D) Atomic radius

✅ Answer

C) Electronegativity

---

5. Electron Gain Enthalpy involves:

A) Loss of an electron

B) Gain of an electron

C) Loss of a proton

D) Gain of a neutron

✅ Answer

B) Gain of an electron

---

6. EGE is generally expressed in:

A) kJ mol⁻¹

B) metre

C) kg

D) litre

✅ Answer

A) kJ mol⁻¹

---

7. EGE is defined for:

A) An isolated gaseous atom

B) A molecule only

C) A solid only

D) A liquid only

✅ Answer

A) An isolated gaseous atom

---

8. Which property is relative and dimensionless?

A) EGE

B) Electronegativity

C) Enthalpy

D) Ionization enthalpy

✅ Answer

B) Electronegativity

---

9. Which quantity represents an energy change?

A) Electronegativity

B) Electron Gain Enthalpy

C) Atomic number

D) Electronegativity scale

✅ Answer

B) Electron Gain Enthalpy

---

10. In electronegativity, the electrons being attracted are:

A) Core electrons

B) Shared/bonding electrons

C) Nuclear electrons

D) Neutrons

✅ Answer

B) Shared/bonding electrons

---

11. Which element has the highest electronegativity?

A) F

B) Cl

C) O

D) N

✅ Answer

A) Fluorine

---

12. Electronegativity generally increases:

A) Down a group

B) From left to right across a period

C) From right to left only

D) Randomly

✅ Answer

B

---

13. Electron gain enthalpy is concerned with:

A) Attraction of shared electrons

B) Energy change on electron addition

C) Bond length only

D) Atomic mass only

✅ Answer

B

---

14. Which statement is correct?

A) Electronegativity has units of kJ mol⁻¹

B) EGE is dimensionless

C) Electronegativity is dimensionless

D) Both are identical quantities

✅ Answer

C

---

15. The process represented by X(g) + e⁻ → X⁻(g) is related to:

A) Electronegativity

B) Electron Gain Enthalpy

C) Atomic radius

D) Metallic character

✅ Answer

B

---

16. Electronegativity is mainly useful in understanding:

A) Bond polarity

B) Nuclear mass

C) Radioactive decay only

D) Atomic mass number

✅ Answer

A) Bond polarity

---

17. A highly electronegative atom strongly attracts:

A) Shared electron pair

B) Neutrons

C) Protons from nucleus

D) Atomic nuclei only

✅ Answer

A

---

18. Which is NOT a difference between electronegativity and EGE?

A) Electronegativity is dimensionless

B) EGE is an energy change

C) Electronegativity concerns shared electrons

D) Both have exactly the same definition

✅ Answer

D

---

19. EGE can be positive or negative depending on:

A) Energy change accompanying electron addition

B) Atomic colour

C) Melting point only

D) Density only

✅ Answer

A

---

20. Which pair is correctly matched?

A) Electronegativity – kJ mol⁻¹

B) EGE – Pauling scale

C) Electronegativity – attraction for shared electrons

D) EGE – attraction for shared electrons

✅ Answer

C

Q. Define electronegativity and electron gain enthalpy.

Solution:

Electronegativity: The tendency of an atom in a chemical bond to attract the shared electron pair towards itself.

Electron Gain Enthalpy: The enthalpy change when an isolated gaseous atom gains an electron to form a negative ion.

Q. Differentiate between electronegativity and electron gain enthalpy.

Solution:

• Electronegativity is the tendency to attract shared electrons in a chemical bond.
• Electron gain enthalpy is the energy change when an isolated gaseous atom gains an electron.
• Electronegativity is dimensionless, whereas EGE is expressed in kJ mol⁻¹.

Q. Explain the difference between electronegativity and electron gain enthalpy with suitable points.

Solution:

Basis	Electronegativity	Electron Gain Enthalpy
Meaning	Attraction for shared electrons	Energy change on gaining electron
Atom	Atom in a chemical bond	Isolated gaseous atom
Nature	Relative property	Thermodynamic quantity
Unit	Dimensionless	kJ mol⁻¹

Q. Define electronegativity. Explain how it differs from electron gain enthalpy.

Solution:

Electronegativity is the tendency of an atom in a molecule to attract the shared pair of electrons towards itself. It is a relative and dimensionless property.

Electron gain enthalpy is the enthalpy change associated with the addition of an electron to an isolated gaseous atom.

Electronegativity
Chemical bond → Shared electrons → Relative attraction

EGE
Isolated gaseous atom → Electron added → Energy change

Thus, although both concepts are related to the tendency of atoms to attract electrons, they are not the same quantity.

Electronegativity describes electron attraction in a bond, whereas EGE describes the energy change on electron addition to an isolated gaseous atom.

Q. Define electronegativity and electron gain enthalpy. Compare their nature, conditions and significance.

1. Electronegativity

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons towards itself.

It is a relative and dimensionless quantity. The Pauling scale is commonly used to compare electronegativities of elements.

2. Electron Gain Enthalpy

Electron gain enthalpy is the enthalpy change when an isolated gaseous atom accepts an electron to form a gaseous anion.

X(g) + e⁻ → X⁻(g)

It is an energy-related quantity and is expressed in kJ mol⁻¹. It may be negative when energy is released or positive when energy is absorbed.

3. Major Differences

Point	Electronegativity	EGE
Definition	Attraction for shared electron pair	Energy change on electron gain
Condition	Atom in chemical bond	Isolated gaseous atom
Nature	Relative property	Thermodynamic quantity
Unit	No unit	kJ mol⁻¹
Use	Helps explain bond polarity	Shows energetics of electron addition

Final Conclusion:

Electronegativity and electron gain enthalpy are related but different concepts. Electronegativity is the relative tendency of an atom in a chemical bond to attract shared electrons, while electron gain enthalpy is the actual enthalpy change associated with adding an electron to an isolated gaseous atom.

🎯 Quick Revision

Electronegativity: Attraction for shared electrons
Condition: Atom in chemical bond
Nature: Relative & dimensionless
EGE: Energy change on electron gain
Condition: Isolated gaseous atom
Unit: kJ mol⁻¹