Anand Classes provides the best study material and notes for JEE, NEET, and CBSE students, helping them master important concepts like electron gain enthalpy. In this article, we explain which of the elements P, S, Cl, and F has the most negative and least negative electron gain enthalpy, with clear reasoning and exam-oriented explanations. Click the print button to download study material and notes.
Which of the following Elements will have the most negative electron gain enthalpy and which the least negative? Elements : P, S, Cl, F
Solution:
The given elements can be placed in the periodic table as follows:
Group No.
15
16
17
2nd Period
–
–
F
3rd Period
P
S
Cl
Across a Period (Left to Right): Electron gain enthalpy becomes more negative as we move across a period from left to right.
Down a Group (Top to Bottom): Electron gain enthalpy becomes less negative as we move down a group because atomic size increases and the added electron experiences less attraction from the nucleus.
Comparison of the Given Elements:
Phosphorus (P): Being in Group 15, it has relatively stable half-filled orbitals. Thus, it resists gaining an extra electron. Hence, it has the least negative electron gain enthalpy.
Fluorine (F): Although it is very electronegative, the incoming electron has to enter the small 2p orbital where strong inter-electronic repulsions occur. This makes its electron gain enthalpy less negative than expected.
Chlorine (Cl): The incoming electron enters the larger 3p orbital, where repulsions are comparatively less. As a result, Cl has more negative electron gain enthalpy than F.
Final Answer:
Most negative electron gain enthalpy → Cl
Least negative electron gain enthalpy → P
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