MCQ Detailed View

Noble gases, also known as Group 18 elements in the modern periodic table, include helium, neon, argon, krypton, xenon, and radon. In older versions of the periodic classification, they were placed in the zero group, hence the name “zero group elements.”

The term arises because of their unique chemical behavior:

1. 
   

   Zero Valency:
   Valency refers to the combining capacity of an element. Most elements form chemical bonds to complete their outer electron shell. However, noble gases already possess completely filled outer shells (helium has 2 electrons; others have 8). Since their octet is already complete, they do not need to gain, lose, or share electrons. This gives them a valency of zero.

   
   


2. 
   

   Zero Electronegativity (or extremely low values):
   Electronegativity is the tendency of an atom to attract shared electrons in a bond. Since noble gases hardly form bonds, their effective electronegativity is nearly zero. Helium, neon, and argon, for example, are extremely inert. Xenon and krypton can form compounds under special conditions, but still, their values are very low compared to other elements.

   
   


3. 
   

   Inertness:
   This zero valency and zero electronegativity together explain why noble gases are chemically inert under ordinary conditions. They rarely participate in chemical reactions, which historically justified their placement in the zero group of the periodic table.

   
   

Key Points for Students:

• 
  

  Noble gases = Group 18 (modern periodic table).

  
  


• 
  

  Old notation = Zero group.

  
  


• 
  

  Reason = Zero valency + Zero electronegativity.

  
  


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  Examples = He, Ne, Ar (completely inert); Kr, Xe (can form a few compounds under extreme conditions).

  
  

Thus, noble gases are called zero group elements due to zero valency and nearly zero electronegativity.