Group 18 Elements: The Noble Gases
Complete Octets, High Stability, and Atmospheric Occurrence.
At the extreme right of the periodic table lies Group 18. Unlike the violently reactive Halogens or Alkali metals, the elements of this group are characterized by their extreme chemical unreactivity. They exist as colorless, odorless, monoatomic gases at room temperature.
1. Meet the Noble Gases
Group 18 consists of Helium ($He$), Neon ($Ne$), Argon ($Ar$), Krypton ($Kr$), Xenon ($Xe$), Radon ($Rn$), and the synthetically produced super-heavy element Oganesson ($Og$).
Historically, they were called "Inert Gases" because chemists believed they could not form any compounds. However, in 1962, Neil Bartlett synthesized the first Xenon compound. Since they do react under specific, extreme conditions, they are now more accurately termed "Noble Gases" (similar to noble metals like Gold and Platinum, which react reluctantly).
Figure 1: All elements in Group 18 are monoatomic gases at room temperature due to weak interatomic forces.
2. Electronic Configuration & Stability
All noble gases have general electronic configuration $ns^2 np^6$, except helium which has $1s^2$.
Because their outermost shell is completely filled (a stable octet/duplet), they have no tendency to lose, gain, or share electrons. This directly explains two of their most important properties:
3. Occurrence in Nature
Where do we find elements that refuse to react with anything? Mostly floating freely in the atmosphere, or trapped underground.
A. The Atmosphere
All noble gases (except Radon and Oganesson) occur in the Earth's atmosphere.
- Their total atmospheric abundance in dry air is ~1% by volume.
- Argon ($Ar$) is the major constituent of this 1%.
B. Helium Sources
The main commercial source of Helium is natural gas. Helium is also found trapped in minerals of radioactive origin, such as pitchblende, monazite, and cleveite (due to alpha decay of uranium and thorium).
C. Radioactive Decay (Radon)
Radon ($Rn$) is obtained as a decay product of Radium-226.
Oganesson ($Og$) is synthetically produced by colliding Californium ($Cf$) with Calcium ($Ca$) ions. It is highly radioactive with a half-life of less than a millisecond.
Mastery Check: Group 18 Intro
15 High-Yield Questions to test your JEE/NEET Preparation
🚀 Complete Guide to the p-Block
Master Inorganic Chemistry. Dive deep into the trends, anomalous properties, and compounds of Groups 15, 16, 17, and 18 for JEE Advanced, JEE Main and NEET.
Explore the p-Block Master Hub
No comments:
Post a Comment