📘 Answer
Across the second period, from Li → F, electronegativity generally increases from left to right.
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.
↓
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:
✅ Answer
B) Increases
2. Which element has the highest electronegativity among Li, Be, B, C, N, O and F?
✅ Answer
D) F
3. Which element has the lowest electronegativity?
✅ Answer
A) Li
4. The increase in electronegativity across a period is mainly due to:
✅ Answer
B) Increase in effective nuclear charge
5. From Li to F, the number of electron shells:
✅ Answer
C) Remains the same
6. Atomic radius across the second period generally:
✅ Answer
B) Decreases
7. Which has greater electronegativity?
✅ Answer
B) F
8. Across a period, effective nuclear charge generally:
✅ Answer
A) Increases
9. Which element is most electronegative?
✅ Answer
D) F
10. Electronegativity represents the tendency to attract:
✅ Answer
C) Shared electron pair
11. The correct increasing order is:
✅ Answer
B) C < N < O < F
12. Which has the smallest atomic size among Li to F?
✅ Answer
D) F
13. Electronegativity generally increases from:
✅ Answer
B) Left to right
14. Which factor opposes the attraction of the nucleus for valence electrons?
✅ Answer
A) Shielding effect
15. Which has higher electronegativity?
✅ Answer
B) C
16. Fluorine has high electronegativity mainly because of its:
✅ Answer
B
17. Which sequence represents decreasing electronegativity?
✅ Answer
B
18. Across a period, nuclear charge:
✅ Answer
A) Increases
19. Electronegativity of Li is lower than F because Li has:
✅ Answer
A) Larger atomic size
20. The overall trend across Li → F is:
✅ 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.
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.
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.
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.
↓
Effective Nuclear Charge ↑
↓
Atomic Radius ↓
↓
Attraction for Shared Electrons ↑
↓
Electronegativity ↑
Li < Be < B < C < N < O < F
🎯 Quick Revision
Atomic size: ↓
Effective nuclear charge: ↑
Number of shells: Same
Highest in Li → F: F
Order: Li < Be < B < C < N < O < F
