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Difficulty: MediumNoble Gases: Isolation, Electronic Structure, and Uses

Helium, neon, and argon are Group 0 (Group 18) elements known for their extreme chemical unreactivity. Which statement accurately explains why helium exhibits this noble behavior despite having only two valence electrons (1s21s^2), unlike the octet configuration (ns2np6ns^2 np^6) of other noble gases?

  1. Its single energy level (n=1n=1) holds a maximum of two electrons, forming a completely filled and highly stable duplet shell.Answer
  2. B
    Its 1s21s^2 valence electrons easily form covalent bonds with electronegative non-metals to satisfy octet stability.
  3. C
    It readily ionizes under ambient conditions to produce a stable He2+He^{2+} cation with a completely empty electron orbital.
  4. D
    Its exceptionally low boiling point during fractional distillation allows it to gain electrons from surrounding atmospheric gases.

Answer

Helium achieves chemical inertness because its single energy level (n=1n=1) is completely filled with two electrons (1s21s^2), forming a stable duplet shell.
Helium has an atomic number of 2, placing its two electrons in the 1s1s orbital (1s21s^2). Because the first principal energy level (n=1n=1) can hold at most two electrons, this shell is completely filled, conferring maximum thermodynamic and chemical stability (duplet rule) without needing an octet.

Step-by-Step Solution

1
Analyze the electronic configuration of helium (Z=2Z=2).
Helium has an electronic configuration of 1s21s^2.
The principal quantum number n=1n=1 contains only the ss subshell, which holds a maximum of 2 electrons (2n2=2(1)2=22n^2 = 2(1)^2 = 2).
2
Compare the stability criteria for n=1n=1 versus higher energy levels (n≥2n \ge 2).
For n=1n=1, two electrons create a completely filled valence shell (duplet stability). For n≥2n \ge 2, eight electrons (ns2np6ns^2 np^6) are required for a full valence shell (octet stability).
Chemical unreactivity is determined by having a completely filled valence shell, which minimizes chemical potential energy.

Key Concept

Duplet vs Octet Stability in Noble Gases
Estimated Time:1m 0s
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Topics

Noble Gases: Isolation, Electronic Structure, and Uses

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