Why do Noble Gases have large positive EGE?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

Noble gases have large positive electron gain enthalpy (EGE) because they possess a completely filled and highly stable valence shell. Their electronic configurations are ns²np⁶, except helium, which has 1s².

He → 1s²

Ne → 2s² 2p⁶

Ar → 3s² 3p⁶

If an additional electron is added to a noble gas atom, it cannot enter the already completely filled valence shell. It must enter a new, higher-energy shell.

Stable filled shell + Incoming electron → Strong repulsion + Higher-energy orbital

⚛️ Why is the value positive?

• Noble gases already have a stable complete valence shell.
• Adding another electron disturbs this stable configuration.
• The incoming electron must occupy a new, higher-energy orbital.
• Energy must therefore be supplied to add the electron.
• Hence, their electron gain enthalpy is large and positive.

🔹 Example: Neon

Neon has the electronic configuration:

Ne = 1s² 2s² 2p⁶

Its second shell is completely filled. An additional electron would have to enter the third shell, which is higher in energy. Therefore, energy is required for electron addition.

Therefore, noble gases have large positive EGE.

✅ Final Answer

Noble gases have large positive electron gain enthalpy because they possess a completely filled and stable valence shell. An additional electron has to enter a new, higher-energy shell and is also repelled by the existing electrons. Therefore, energy must be supplied, making their EGE large and positive.

20 MCQs with Answers

1. Noble gases have large positive EGE because they have:

A) Incomplete valence shell

B) Completely filled valence shell

C) No electrons

D) Only one valence electron

✅ Answer

B) Completely filled valence shell

---

2. The general valence-shell configuration of noble gases is:

A) ns¹

B) ns²np⁶

C) ns²np³

D) ns²np⁵

✅ Answer

B) ns²np⁶

---

3. The exception to ns²np⁶ among noble gases is:

A) Ne

B) Ar

C) He

D) Kr

✅ Answer

C) He

---

4. Helium has the electronic configuration:

A) 1s¹

B) 1s²

C) 2s²

D) 2p⁶

✅ Answer

B) 1s²

---

5. When a noble gas gains an electron, the electron enters:

A) The same completely filled orbital

B) A lower-energy shell

C) A new higher-energy shell

D) The nucleus

✅ Answer

C) A new higher-energy shell

---

6. Positive EGE means:

A) Energy is released

B) Energy is absorbed

C) No energy change

D) Nuclear energy is released

✅ Answer

B) Energy is absorbed

---

7. Noble gases are chemically stable mainly because of:

A) Half-filled shell

B) Completely filled valence shell

C) One electron

D) High mass

✅ Answer

B

---

8. Which element has a completely filled second shell?

A) F

B) O

C) Ne

D) N

✅ Answer

C) Ne

---

9. Which noble gas has configuration 1s²?

A) He

B) Ne

C) Ar

D) Kr

✅ Answer

A) He

---

10. Adding an electron to a noble gas generally:

A) Releases large energy

B) Requires energy

C) Requires no energy

D) Removes an electron

✅ Answer

B) Requires energy

---

11. Which group contains noble gases?

A) Group 1

B) Group 2

C) Group 17

D) Group 18

✅ Answer

D) Group 18

---

12. Which has a more stable valence-shell configuration?

A) Na

B) Cl

C) Ne

D) Mg

✅ Answer

C) Ne

---

13. Noble gases have very low tendency to:

A) Exist as atoms

B) Gain an additional electron

C) Have electrons

D) Have nuclei

✅ Answer

B

---

14. Which of the following has the configuration ns²np⁶?

A) Halogens

B) Noble gases except He

C) Alkali metals

D) Transition metals

✅ Answer

B

---

15. The incoming electron in a noble gas experiences:

A) No repulsion

B) Electron-electron repulsion

C) Proton-proton repulsion only

D) Nuclear decay

✅ Answer

B

---

16. Which has a completely filled octet?

A) Ne

B) F

C) O

D) N

✅ Answer

A) Ne

---

17. Noble gases have high resistance to electron addition because:

A) Their valence shell is already complete

B) They have no nucleus

C) They have one electron

D) They are metals

✅ Answer

A

---

18. Which statement is correct?

A) Noble gases have highly negative EGE

B) Noble gases generally have positive EGE

C) Noble gases have no electrons

D) Noble gases are halogens

✅ Answer

B

---

19. The stable configuration of neon is:

A) 1s²2s²2p⁴

B) 1s²2s²2p⁵

C) 1s²2s²2p⁶

D) 1s²2s²

✅ Answer

C) 1s²2s²2p⁶

---

20. The main reason for positive EGE of noble gases is:

A) Electron addition gives a more stable configuration

B) Electron addition disturbs their stable configuration

C) They have no valence electrons

D) They readily form anions

✅ Answer

B

Q. Why do noble gases have large positive electron gain enthalpy?

Solution: Noble gases have completely filled and stable valence shells. An additional electron must enter a new, higher-energy shell and is strongly repelled by the existing electrons. Therefore, energy is required and their EGE is large and positive.

Complete shell → Stable configuration → Electron addition requires energy → Positive EGE

Q. Explain the reason for the positive electron gain enthalpy of noble gases.

Solution:

• Noble gases have completely filled valence shells.
• They have highly stable electronic configurations.
• An additional electron has to enter a new and higher-energy shell.
• Therefore, energy must be supplied for electron addition.

Hence, noble gases have large positive electron gain enthalpy.

Q. Explain why noble gases have positive EGE, whereas halogens generally have negative EGE.

Solution:

Noble Gases	Halogens
Valence shell completely filled	One electron short of stable configuration
Additional electron enters a new shell	Additional electron completes the valence shell
Energy is required	Energy is generally released
Positive EGE	Negative EGE

Q. Discuss the electronic configuration and electron gain enthalpy of noble gases.

Solution:

Noble gases are placed in Group 18 of the periodic table. Except helium, their general valence-shell configuration is ns²np⁶.

He = 1s²

Ne = 1s²2s²2p⁶

Ar = [Ne]3s²3p⁶

These configurations represent completely filled and highly stable valence shells. Therefore, noble gases have very little tendency to accept an additional electron.

If an electron is added, it has to enter a new, higher-energy shell. The incoming electron also experiences repulsion from the electrons already present. Hence, energy is absorbed.

Therefore, noble gases have large positive electron gain enthalpy.

Q. Explain in detail why noble gases have large positive electron gain enthalpy.

Detailed Solution

Noble gases are chemically stable elements belonging to Group 18. Their stability arises from their completely filled valence shells.

1. Stable Electronic Configuration

Except helium, noble gases have the general configuration:

ns²np⁶

Helium has the stable configuration:

1s²

2. Addition of an Electron

When an additional electron is supplied to a noble gas atom, the existing valence shell is already completely filled. Therefore, the new electron cannot be accommodated in the same shell without violating the available orbital capacity.

It must occupy an orbital in the next higher principal energy level. This requires energy.

3. Electron-Electron Repulsion

The incoming electron is also repelled by the electrons already present in the atom. Thus, additional energy is required to force the electron into the atom.

Complete valence shell
↓
Very stable configuration
↓
Incoming electron enters higher-energy shell
↓
Energy absorbed
↓
Large positive EGE

4. Comparison with Halogens

Halogens have seven valence electrons. They can achieve a stable noble-gas configuration by accepting one electron. Therefore, their first electron gain enthalpy is generally negative.

Noble gases already possess the stable configuration, so accepting another electron is energetically unfavourable.

Final Answer:

Noble gases have large positive EGE because their valence shells are already completely filled and highly stable. An additional electron must enter a higher-energy shell and experiences electron-electron repulsion. Hence, energy must be supplied, resulting in a large positive electron gain enthalpy.

🎯 Quick Revision

Noble Gases: Group 18
Configuration: ns²np⁶ (He = 1s²)
Valence Shell: Completely filled
Electron Addition: Unfavourable
Incoming Electron: Enters higher-energy shell
Result: Energy absorbed
EGE: Large positive

Why do Noble Gases have large positive EGE?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

Noble gases have large positive electron gain enthalpy (EGE) because they possess a completely filled and highly stable valence shell. Their electronic configurations are ns²np⁶, except helium, which has 1s².

He → 1s²

Ne → 2s² 2p⁶

Ar → 3s² 3p⁶

If an additional electron is added to a noble gas atom, it cannot enter the already completely filled valence shell. It must enter a new, higher-energy shell.

Stable filled shell + Incoming electron → Strong repulsion + Higher-energy orbital

⚛️ Why is the value positive?

• Noble gases already have a stable complete valence shell.
• Adding another electron disturbs this stable configuration.
• The incoming electron must occupy a new, higher-energy orbital.
• Energy must therefore be supplied to add the electron.
• Hence, their electron gain enthalpy is large and positive.

🔹 Example: Neon

Neon has the electronic configuration:

Ne = 1s² 2s² 2p⁶

Its second shell is completely filled. An additional electron would have to enter the third shell, which is higher in energy. Therefore, energy is required for electron addition.

Therefore, noble gases have large positive EGE.

✅ Final Answer

Noble gases have large positive electron gain enthalpy because they possess a completely filled and stable valence shell. An additional electron has to enter a new, higher-energy shell and is also repelled by the existing electrons. Therefore, energy must be supplied, making their EGE large and positive.

20 MCQs with Answers

1. Noble gases have large positive EGE because they have:

A) Incomplete valence shell

B) Completely filled valence shell

C) No electrons

D) Only one valence electron

✅ Answer

B) Completely filled valence shell

---

2. The general valence-shell configuration of noble gases is:

A) ns¹

B) ns²np⁶

C) ns²np³

D) ns²np⁵

✅ Answer

B) ns²np⁶

---

3. The exception to ns²np⁶ among noble gases is:

A) Ne

B) Ar

C) He

D) Kr

✅ Answer

C) He

---

4. Helium has the electronic configuration:

A) 1s¹

B) 1s²

C) 2s²

D) 2p⁶

✅ Answer

B) 1s²

---

5. When a noble gas gains an electron, the electron enters:

A) The same completely filled orbital

B) A lower-energy shell

C) A new higher-energy shell

D) The nucleus

✅ Answer

C) A new higher-energy shell

---

6. Positive EGE means:

A) Energy is released

B) Energy is absorbed

C) No energy change

D) Nuclear energy is released

✅ Answer

B) Energy is absorbed

---

7. Noble gases are chemically stable mainly because of:

A) Half-filled shell

B) Completely filled valence shell

C) One electron

D) High mass

✅ Answer

B

---

8. Which element has a completely filled second shell?

A) F

B) O

C) Ne

D) N

✅ Answer

C) Ne

---

9. Which noble gas has configuration 1s²?

A) He

B) Ne

C) Ar

D) Kr

✅ Answer

A) He

---

10. Adding an electron to a noble gas generally:

A) Releases large energy

B) Requires energy

C) Requires no energy

D) Removes an electron

✅ Answer

B) Requires energy

---

11. Which group contains noble gases?

A) Group 1

B) Group 2

C) Group 17

D) Group 18

✅ Answer

D) Group 18

---

12. Which has a more stable valence-shell configuration?

A) Na

B) Cl

C) Ne

D) Mg

✅ Answer

C) Ne

---

13. Noble gases have very low tendency to:

A) Exist as atoms

B) Gain an additional electron

C) Have electrons

D) Have nuclei

✅ Answer

B

---

14. Which of the following has the configuration ns²np⁶?

A) Halogens

B) Noble gases except He

C) Alkali metals

D) Transition metals

✅ Answer

B

---

15. The incoming electron in a noble gas experiences:

A) No repulsion

B) Electron-electron repulsion

C) Proton-proton repulsion only

D) Nuclear decay

✅ Answer

B

---

16. Which has a completely filled octet?

A) Ne

B) F

C) O

D) N

✅ Answer

A) Ne

---

17. Noble gases have high resistance to electron addition because:

A) Their valence shell is already complete

B) They have no nucleus

C) They have one electron

D) They are metals

✅ Answer

A

---

18. Which statement is correct?

A) Noble gases have highly negative EGE

B) Noble gases generally have positive EGE

C) Noble gases have no electrons

D) Noble gases are halogens

✅ Answer

B

---

19. The stable configuration of neon is:

A) 1s²2s²2p⁴

B) 1s²2s²2p⁵

C) 1s²2s²2p⁶

D) 1s²2s²

✅ Answer

C) 1s²2s²2p⁶

---

20. The main reason for positive EGE of noble gases is:

A) Electron addition gives a more stable configuration

B) Electron addition disturbs their stable configuration

C) They have no valence electrons

D) They readily form anions

✅ Answer

B

Q. Why do noble gases have large positive electron gain enthalpy?

Solution: Noble gases have completely filled and stable valence shells. An additional electron must enter a new, higher-energy shell and is strongly repelled by the existing electrons. Therefore, energy is required and their EGE is large and positive.

Complete shell → Stable configuration → Electron addition requires energy → Positive EGE

Q. Explain the reason for the positive electron gain enthalpy of noble gases.

Solution:

• Noble gases have completely filled valence shells.
• They have highly stable electronic configurations.
• An additional electron has to enter a new and higher-energy shell.
• Therefore, energy must be supplied for electron addition.

Hence, noble gases have large positive electron gain enthalpy.

Q. Explain why noble gases have positive EGE, whereas halogens generally have negative EGE.

Solution:

Noble Gases	Halogens
Valence shell completely filled	One electron short of stable configuration
Additional electron enters a new shell	Additional electron completes the valence shell
Energy is required	Energy is generally released
Positive EGE	Negative EGE

Q. Discuss the electronic configuration and electron gain enthalpy of noble gases.

Solution:

Noble gases are placed in Group 18 of the periodic table. Except helium, their general valence-shell configuration is ns²np⁶.

He = 1s²

Ne = 1s²2s²2p⁶

Ar = [Ne]3s²3p⁶

These configurations represent completely filled and highly stable valence shells. Therefore, noble gases have very little tendency to accept an additional electron.

If an electron is added, it has to enter a new, higher-energy shell. The incoming electron also experiences repulsion from the electrons already present. Hence, energy is absorbed.

Therefore, noble gases have large positive electron gain enthalpy.

Q. Explain in detail why noble gases have large positive electron gain enthalpy.

Detailed Solution

Noble gases are chemically stable elements belonging to Group 18. Their stability arises from their completely filled valence shells.

1. Stable Electronic Configuration

Except helium, noble gases have the general configuration:

ns²np⁶

Helium has the stable configuration:

1s²

2. Addition of an Electron

When an additional electron is supplied to a noble gas atom, the existing valence shell is already completely filled. Therefore, the new electron cannot be accommodated in the same shell without violating the available orbital capacity.

It must occupy an orbital in the next higher principal energy level. This requires energy.

3. Electron-Electron Repulsion

The incoming electron is also repelled by the electrons already present in the atom. Thus, additional energy is required to force the electron into the atom.

Complete valence shell
↓
Very stable configuration
↓
Incoming electron enters higher-energy shell
↓
Energy absorbed
↓
Large positive EGE

4. Comparison with Halogens

Halogens have seven valence electrons. They can achieve a stable noble-gas configuration by accepting one electron. Therefore, their first electron gain enthalpy is generally negative.

Noble gases already possess the stable configuration, so accepting another electron is energetically unfavourable.

Final Answer:

Noble gases have large positive EGE because their valence shells are already completely filled and highly stable. An additional electron must enter a higher-energy shell and experiences electron-electron repulsion. Hence, energy must be supplied, resulting in a large positive electron gain enthalpy.

🎯 Quick Revision

Noble Gases: Group 18
Configuration: ns²np⁶ (He = 1s²)
Valence Shell: Completely filled
Electron Addition: Unfavourable
Incoming Electron: Enters higher-energy shell
Result: Energy absorbed
EGE: Large positive

Why is the EGE of Chlorine more negative than Fluorine?

📚 Chapter: Classification of Elements and Periodicity in Properties

📘 Answer

The electron gain enthalpy (EGE) of chlorine is more negative than that of fluorine because the incoming electron enters the larger 3p orbital of chlorine, where electron-electron repulsion is less than in the very small 2p orbital of fluorine.

Cl: [Ne] 3s² 3p⁵

F: [He] 2s² 2p⁵

Although fluorine has a higher effective nuclear charge, its very small atomic size causes considerable repulsion between the incoming electron and the electrons already present in the compact 2p subshell.

⚛️ Comparison

F → Small 2p orbital → High electron-electron repulsion

Cl → Larger 3p orbital → Less electron-electron repulsion

Therefore, chlorine can accommodate the incoming electron more easily than fluorine, releasing more energy.

EGE(Cl) < EGE(F)

Hence, the EGE of chlorine is more negative than that of fluorine.

🔹 Important Exam Point

The expected trend of electron gain enthalpy in Group 17 is not perfectly regular. Fluorine has a less negative EGE than chlorine because of its extremely small size and greater electron-electron repulsion in the compact 2p subshell.

Cl has the most negative electron gain enthalpy among the halogens.

✅ Final Answer

Chlorine has a more negative EGE than fluorine because its incoming electron enters the larger 3p orbital, where electron-electron repulsion is lower. In fluorine, the incoming electron enters the very small 2p orbital, causing greater repulsion.

EGE(Cl) < EGE(F)

20 MCQs with Answers

1. Which has more negative electron gain enthalpy?

A) Fluorine

B) Chlorine

C) Oxygen

D) Nitrogen

✅ Answer

B) Chlorine

---

2. The incoming electron in fluorine enters the:

A) 1s orbital

B) 2p orbital

C) 3p orbital

D) 3d orbital

✅ Answer

B) 2p orbital

---

3. The incoming electron in chlorine enters the:

A) 2p orbital

B) 3s orbital

C) 3p orbital

D) 4s orbital

✅ Answer

C) 3p orbital

---

4. Why is EGE of F less negative than Cl?

A) F has no nucleus

B) F has a very small 2p orbital

C) Cl has fewer electrons

D) F is a metal

✅ Answer

B

---

5. Greater electron-electron repulsion occurs in:

A) Large 3p orbital

B) Compact 2p orbital

C) 4s orbital only

D) 3d orbital only

✅ Answer

B

---

6. Fluorine belongs to:

A) Group 1

B) Group 2

C) Group 17

D) Group 18

✅ Answer

C) Group 17

---

7. Chlorine belongs to:

A) Group 15

B) Group 16

C) Group 17

D) Group 18

✅ Answer

C) Group 17

---

8. Chlorine has the configuration:

A) [He] 2s²2p⁵

B) [Ne] 3s²3p⁵

C) [Ne] 3s²3p⁶

D) [Ar] 4s¹

✅ Answer

B

---

9. Fluorine has the configuration:

A) [He] 2s²2p⁵

B) [Ne] 3s²3p⁵

C) [He] 2s²2p⁴

D) [Ne] 3s²3p⁶

✅ Answer

A

---

10. Which factor makes electron addition to F relatively difficult?

A) Very large size

B) Compact size and electron repulsion

C) Absence of electrons

D) Low nuclear charge

✅ Answer

B

---

11. Electron gain enthalpy is generally represented in:

A) kJ mol⁻¹

B) kg mol⁻¹

C) metre

D) litre

✅ Answer

A

---

12. A more negative EGE indicates:

A) Greater tendency to accept an electron

B) Greater tendency to lose a proton

C) No electron affinity

D) No nuclear attraction

✅ Answer

A

---

13. Which subshell is smaller?

A) 3p

B) 2p

C) Both are equal

D) 4p

✅ Answer

B) 2p

---

14. The atomic number of fluorine is:

A) 7

B) 8

C) 9

D) 10

✅ Answer

C) 9

---

15. The atomic number of chlorine is:

A) 16

B) 17

C) 18

D) 19

✅ Answer

B) 17

---

16. The EGE anomaly between F and Cl is mainly due to:

A) Nuclear instability

B) Small size of F

C) Large mass of F

D) Metallic character of F

✅ Answer

B

---

17. Which halogen has the most negative EGE?

A) F

B) Cl

C) Br

D) I

✅ Answer

B) Cl

---

18. Fluorine gains one electron to form:

A) F⁺

B) F²⁺

C) F⁻

D) F²⁻

✅ Answer

C) F⁻

---

19. Chlorine gains one electron to form:

A) Cl⁺

B) Cl⁻

C) Cl²⁺

D) Cl²⁻

✅ Answer

B) Cl⁻

---

20. The main reason for the higher EGE magnitude of Cl compared with F is:

A) Larger 3p orbital reduces electron-electron repulsion

B) Chlorine has no valence electrons

C) Fluorine has no nucleus

D) Chlorine is a noble gas

✅ Answer

A

Q. Why is the electron gain enthalpy of chlorine more negative than fluorine?

Solution: Fluorine is very small, so the incoming electron experiences strong electron-electron repulsion in its compact 2p orbital. In chlorine, the larger 3p orbital provides more space and less repulsion.

Therefore, EGE(Cl) is more negative than EGE(F).

Q. Explain why chlorine has a more negative electron gain enthalpy than fluorine.

Solution:

• Fluorine has a very small atomic size and a compact 2p subshell.
• The incoming electron experiences strong electron-electron repulsion.
• Chlorine has a larger 3p subshell, so electron-electron repulsion is comparatively lower.

Hence, chlorine releases more energy on gaining an electron and its EGE is more negative.

Q. Compare the electron gain enthalpy of fluorine and chlorine and explain the anomaly in Group 17.

Solution:

Normally, electron gain enthalpy is expected to become less negative down a group because atomic size increases. However, fluorine is an exception.

F: Very small 2p orbital → High repulsion

Cl: Larger 3p orbital → Lower repulsion

Thus, the incoming electron is accommodated more comfortably in chlorine than in fluorine.

EGE(Cl) < EGE(F)

Chlorine has the more negative electron gain enthalpy.

Q. Explain the electron gain enthalpy trend in halogens, with special reference to fluorine and chlorine.

Solution:

1. Halogens have seven valence electrons and require one electron to attain a stable noble-gas configuration.
2. Therefore, they generally have highly negative electron gain enthalpies.
3. Fluorine has a very small atomic size and compact 2p orbitals.
4. The incoming electron experiences strong electron-electron repulsion in fluorine.
5. Chlorine has a larger 3p orbital, allowing the incoming electron to be accommodated with less repulsion.

Cl has more negative EGE than F.

Q. Explain in detail why the electron gain enthalpy of chlorine is more negative than fluorine.

Detailed Solution

Both fluorine and chlorine belong to Group 17 and have seven valence electrons. They need one electron to complete their valence shell. Therefore, both have a strong tendency to accept an electron.

Electronic Configurations

F = 1s² 2s² 2p⁵

Cl = [Ne] 3s² 3p⁵

Fluorine is much smaller than chlorine. The incoming electron in fluorine has to enter the compact 2p orbital. Because the orbital is very small, there is considerable electron-electron repulsion between the incoming electron and the electrons already present.

In chlorine, the incoming electron enters the larger 3p orbital. The greater size of the orbital provides more space and reduces electron-electron repulsion.

Small 2p orbital (F)
↓
Greater repulsion

Larger 3p orbital (Cl)
↓
Less repulsion

Hence, chlorine releases more energy when it gains an electron. Therefore, its electron gain enthalpy is more negative than that of fluorine.

Final Answer:

EGE(Cl) < EGE(F)

The unusual trend is mainly due to the very small size of fluorine and the high electron-electron repulsion in its compact 2p subshell.

🎯 Quick Revision

F: Small 2p orbital → More repulsion
Cl: Larger 3p orbital → Less repulsion

EGE(Cl) < EGE(F)

Exam Point: Chlorine has the most negative electron gain enthalpy among the halogens.