Which one of the following arrangements represents the correct order of electron gain enthalpy (with negative sign) of the given atomic species ?
- S < O < Cl < F
- Cl < F < S < O
- F < Cl < O < S
- O < S < F < Cl
Answer
(4) O < S < F < Cl
Solution
As per NCERT, electron gain enthalpy becomes more negative across a period, so group 17 elements are more negative than group 16 elements.
∵ O and F are very small, the added electron goes into a compact 2p subshell and feels strong inter-electronic repulsion.
⇒ Their electron gain enthalpy is less negative than that of the next members, S and Cl.
∴ O < S (group 16) and F < Cl (group 17), and group 16 < group 17:
O < S < F < Cl
(Values: O -141, S -200, F -328, Cl -349 kJ mol-1)
Answer: (4)