Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Metallic character decreases and non-metallic character increases on moving from left to right in a period.
Reason (R) : It is due to increase in ionisation enthalpy and decrease in electron gain enthalpy, when one moves from left to right in a period.
In the light of the above statements, choose the most appropriate answer from the options given below :
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Metallic character is directly proportional to atomic radius and inversely proportional to ionization energy. Non-metallic character follows the exact opposite trend.
Both (A) and (R) are correct and (R) is the correct explanation of (A).
Both (A) and (R) are correct but (R) is not the correct explanation of (A).
(A) is true but (R) is false.
(A) is false but (R) is true.
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Concept:
Metallic character is the tendency of an element to lose electrons (electropositivity), whereas non-metallic character is the tendency to gain electrons (electronegativity). Step 2: Detailed Explanation:
1. Trends in a Period: As we move from left to right across a period, the atomic size decreases and the effective nuclear charge increases.
2. Ionization Enthalpy: Due to the increased nuclear pull, it becomes harder to remove an electron. Thus, Ionization Enthalpy increases. High IE leads to a decrease in the tendency to lose electrons, thereby decreasing metallic character.
3. Electron Gain Enthalpy: As the nuclear charge increases, the atoms have a greater affinity for electrons. The electron gain enthalpy generally becomes more negative (often phrased as "decreases" in the sense of becoming more exothermic). This increases non-metallic character.
4. Relationship: The changes in these energy parameters directly cause the shifts in chemical character described in the assertion. Step 3: Final Answer:
Both statements are scientifically accurate, and the reason provides the fundamental cause for the observed periodic trend.
