Why do noble gases have very high I.E.?

1. Why do noble gases have very high I.E.? +

Correct Answer

Noble gases have very high first ionization enthalpy because they possess a highly stable, completely filled valence shell.

Detailed Solution

Noble gases such as He, Ne, Ar, Kr, Xe and Rn have exceptionally stable electronic configurations. Their general valence-shell configurations are:

He: 1s²
Ne: 2s² 2p⁶
Ar: 3s² 3p⁶
Kr: 4s² 4p⁶

Except for helium, the outermost shell has the stable configuration:

ns²np⁶

This is a completely filled valence shell. Removing an electron from this stable configuration requires a large amount of energy. Therefore, noble gases have very high first ionization enthalpy.

Main Reasons

1. Completely filled valence shell:
The stable octet configuration makes electron removal difficult.

2. High effective nuclear attraction:
The valence electrons are strongly attracted by the nucleus, particularly because noble gases have relatively high effective nuclear charge within their period.

3. Small atomic size:
Across a period, noble gases have comparatively small atomic radii, so their outer electrons are held strongly by the nucleus.

4. Stable electronic configuration:
Ionization would destroy the exceptionally stable noble-gas configuration.

JEE / NEET Shortcut

Remember:

Stable configuration → difficult electron removal → High IE

For noble gases:

ns²np⁶ → very stable → very high IE₁

Helium is the extreme case because it has a very small 1s² shell and therefore has the highest first ionization enthalpy of all elements.

Periodic Trend

Noble gases generally have the highest first ionization enthalpy in their respective periods. For example, in Period 2:

Li → Be → B → C → N → O → F → Ne

Neon has the highest IE₁ in this period. Similarly, in Period 3:

Na → Mg → Al → Si → P → S → Cl → Ar

Argon has the highest IE₁ in this period.

30 Related MCQs with Solutions

1. Why do noble gases have very high ionization enthalpy?

A. They have incomplete shells

B. They have completely filled valence shells

C. They have low nuclear charge

D. They have many unpaired electrons

Answer: B
Complete valence shells are highly stable.

2. The general valence configuration of most noble gases is:

A. ns¹

B. ns²np¹

C. ns²np⁶

D. ns²np⁵

Answer: C. ns²np⁶

3. Which noble gas has the highest first ionization enthalpy?

A. Ne

B. Ar

C. He

D. Kr

Answer: C. He

4. The electronic configuration of Ne is:

A. 1s²2s²2p⁴

B. 1s²2s²2p⁶

C. 1s²2s²2p⁵

D. 1s²2s²2p³

Answer: B

5. Which factor strongly contributes to high IE of noble gases?

A. Large atomic size

B. Stable electronic configuration

C. Low effective nuclear charge

D. High number of shells only

Answer: B

6. Which element has the highest IE₁ in Period 2?

A. F

B. N

C. O

D. Ne

Answer: D. Ne

7. Which element has the highest IE₁ in Period 3?

A. Cl

B. P

C. Ar

D. S

Answer: C. Ar

8. The noble-gas configuration is often called:

A. Unstable configuration

B. Stable closed-shell configuration

C. Half-filled configuration

D. Excited configuration

Answer: B

9. Which noble gas has the configuration 1s²?

A. He

B. Ne

C. Ar

D. Kr

Answer: A. He

10. Ionization of a noble gas requires high energy because:

A. An electron is removed from a stable shell

B. It has no nucleus

C. It has no electrons

D. It is always metallic

Answer: A

11. Which has a completely filled p subshell?

A. C

B. N

C. O

D. Ne

Answer: D. Ne

12. Which noble gas has the smallest atomic radius?

A. He

B. Ne

C. Ar

D. Kr

Answer: A. He

13. Down Group 18, first ionization enthalpy generally:

A. Increases

B. Decreases

C. Remains exactly constant

D. Becomes zero

Answer: B
Atomic size increases down the group.

14. Which has greater IE₁: Ne or Na?

A. Ne

B. Na

C. Equal

D. Cannot compare

Answer: A. Ne

15. Which configuration is associated with a closed shell?

A. ns²np¹

B. ns²np³

C. ns²np⁵

D. ns²np⁶

Answer: D. ns²np⁶

16. Noble gases are generally chemically unreactive because:

A. Their valence shells are incomplete

B. Their valence shells are stable and complete

C. They have low IE

D. They are all metals

Answer: B

17. Which noble gas belongs to Period 3?

A. Ne

B. Ar

C. Kr

D. Xe

Answer: B. Ar

18. Which noble gas belongs to Period 4?

A. Ar

B. Kr

C. Ne

D. Xe

Answer: B. Kr

19. Which statement about He is correct?

A. It has an octet

B. It has a stable duplet

C. It has one electron

D. It is a metal

Answer: B. Stable duplet

20. The highest IE in a period is generally shown by:

A. Alkali metal

B. Alkaline earth metal

C. Halogen

D. Noble gas

Answer: D. Noble gas

21. Which factor decreases down Group 18 and contributes to lower IE?

A. Atomic radius

B. Number of protons

C. Nuclear charge

D. Atomic mass

Answer: A. Atomic radius increases down the group, so IE decreases.

22. Which is harder to ionize?

A. Na

B. Ne

C. K

D. Li

Answer: B. Ne

23. Which has a stable octet?

A. F

B. O

C. Ne

D. N

Answer: C. Ne

24. The valence shell of Ar is:

A. 3s²3p⁶

B. 3s²3p⁵

C. 3s²3p⁴

D. 3s¹3p⁶

Answer: A

25. Which property generally follows the order of noble gases as an exception to metallic trends?

A. Very high IE

B. Very low IE

C. High metallic character

D. Strong electropositivity

Answer: A. Very high IE

26. A noble gas resists loss of an electron because:

A. Its electron is weakly held

B. Its valence shell is already stable

C. It has no electrons

D. Its nucleus is absent

Answer: B

27. Which has a lower IE₁: Ar or Cl?

A. Ar

B. Cl

C. Equal

D. Cannot compare

Answer: B. Cl

28. Which statement is incorrect?

A. Noble gases have stable valence shells

B. Noble gases generally have high IE

C. Helium has the highest IE₁

D. Noble gases readily lose electrons

Answer: D

29. The high IE of noble gases is primarily associated with:

A. Stable closed-shell configuration

B. Half-filled d subshell

C. Low nuclear attraction

D. Large atomic radius

Answer: A

30. Which is the best summary?

A. Noble gases have incomplete shells and low IE

B. Noble gases have complete shells and high IE

C. Noble gases are metals

D. Noble gases have only one electron

Answer: B

Advertisement