Problem 129 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following noble gases do not form any compound? (a) \(\mathrm{Kr}\) (b) \(\mathrm{He}\) (c) Xe (d) Ne

Step-by-Step Solution

Answer

Ne (Neon) does not form any compounds.

Step 1: Understanding Noble Gases

Noble gases are found in Group 18 of the periodic table and include elements like Helium ( He ), Neon ( Ne ), Argon, Krypton ( Kr ), Xenon ( Xe ), and Radon. They are known for their lack of reactivity due to having a full valence electron shell.

Step 2: Identifying the Reactivity

He (Helium) and Ne (Neon) are the least reactive of all noble gases because their outermost electron shell is completely filled, preventing them from forming compounds easily.

Step 3: Noble Gases Known to Form Compounds

While Kr (Krypton) and Xe (Xenon) are stable, they can form compounds under certain conditions. Xenon is more well-known for forming oxides and fluorides, and Krypton can form at least one compound, krypton difluoride.

Step 4: Determining the Inert Noble Gas

Given the choices, He and Ne are inert, but of the options listed, Ne (Neon) is known to be the least reactive and has no known stable compounds.

Key Concepts

Chemical Inertness

Noble gases are celebrated for their chemical inertness. This means they do not easily form compounds with other elements. Why? Because their outer electron shells are full. When an atom has a full shell, it is energetically stable and doesn't seek out other atoms to bond with. This is the case for all noble gases, making them less reactive compared to other elements. For students, it's essential to understand that inertness indicates an element's satisfaction with its current electron count, which minimizes its tendency to engage in chemical reactions. This principle is foundational in chemistry and explains why noble gases remain mostly unreactive.

Noble Gas Compounds

Even though noble gases are generally inert, some can form compounds under specific conditions. The best-known noble gas compounds involve xenon. Xenon can combine with fluoride or oxygen to create compounds such as XeF₂ or XeO₄. Krypton can form krypton difluoride,
KrF₂, although it's much rarer.

• These compounds typically require extreme environments, like high pressures or the presence of strong oxidizing agents.
• Such conditions don't often occur naturally, which is why noble gas compounds are not found in nature.

Understanding these unique cases helps students see exceptions in periodic trends.

Periodic Table Group 18

The noble gases make up Group 18 in the periodic table. They include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

• This group is characterized by elements having complete valence electron shells, typically with eight electrons, except Helium, which has two.
• Being in Group 18, they are at the far right of the periodic table, signifying their stability and non-reactivity.

Understanding the characteristics of Group 18 helps students appreciate why these gases stand apart from other elements in behavior and chemical properties.

Reactivity of Helium and Neon

Helium and Neon, the lightest of the noble gases, are noteworthy for their outstanding lack of reactivity.

• Helium, with only one electron shell filled with two electrons, is completely inert and never forms compounds.
• Neon mirrors this behavior with a full outer shell of eight electrons. This full shell means it has no tendency to react with other elements.

Both of these gases do not engage in chemical reactions under normal conditions, unlike some heavier noble gases. Understanding this lack of reactivity underscores a crucial aspect of chemistry: the stability of filled electron shells signifies true chemical stability.