Understanding Valency and Zero Valency

Valency is defined as the combining capacity of an element. It represents the number of electrons an atom can gain, lose, or share to form chemical bonds with other atoms. Atoms tend to achieve a stable electron configuration, usually like that of the nearest noble gas.

An element having zero valency means that its atoms typically do not form chemical bonds under normal conditions. This lack of reactivity is because the element already has a stable electron configuration, usually a filled outermost electron shell. Elements with zero valency are generally the noble gases.

Analyzing the Options

Let's examine the valency of each given element:

• Sulphur (S): Sulphur is in Group 16 of the periodic table. It typically exhibits valencies such as 2, 4, or 6 to achieve a stable configuration.
• Phosphorous (P): Phosphorous is in Group 15. It commonly shows valencies of 3 or 5 in its compounds.
• Lead (Pb): Lead is in Group 14. Its common valencies are 2 and 4.
• Radon (Rn): Radon is a member of Group 18, the noble gases. Noble gases have a complete valence electron shell (octet rule satisfied, except for Helium). This full shell makes them very stable and unreactive under standard conditions. Therefore, noble gases have a valency of zero.

Identifying the Element with Zero Valency

Based on the analysis, Radon is a noble gas. Noble gases are known for their inertness and lack of chemical reactivity due to their stable electron configuration. This stability corresponds to a combining capacity, or valency, of zero.

Therefore, among the given options, Radon is the element having zero valency.

Revision Table: Valency of Elements

Additional Information: Noble Gases and Valency

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

• They have a general electronic configuration of ns²np⁶ in their outermost shell (except Helium, which has 1s²).
• This stable electron configuration means they have little tendency to gain, lose, or share electrons to form chemical bonds.
• Their chemical inertness is why they are sometimes referred to as inert gases, although some heavier noble gases like Xenon and Krypton can form compounds under specific conditions with highly electronegative elements like Fluorine and Oxygen. However, their primary characteristic is very low reactivity, giving them a valency that is effectively zero for most practical purposes.