Q2 / 180 · COMEDK 2023 (Morning Shift) · Chemistry
The correct decreasing order of negative electron gain enthalpy for $\mathrm{C}, \mathrm{Ca}, \mathrm{Al}, \mathrm{F}$ and $\mathrm{O}$ is
- A$\mathrm{F}>\mathrm{C}>\mathrm{O}>\mathrm{Ca}>\mathrm{Al}$
- B$\mathrm{Al}>\mathrm{F}>\mathrm{Ca}>\mathrm{C}>\mathrm{O}$
- Correct answerC$\mathrm{F}>\mathrm{O}>\mathrm{C}>\mathrm{Al}>\mathrm{Ca}$
- D$\mathrm{Ca}>\mathrm{Al}>\mathrm{O}>\mathrm{F}>\mathrm{C}$
Solution
The electron gain enthalpy is the energy released when an electron is added to a neutral gaseous atom. Generally, it becomes more negative (higher magnitude) across a period from left to right and decreases down a group.
The elements given are $\mathrm{F}$ (Group 17, Period 2), $\mathrm{O}$ (Group 16, Period 2), $\mathrm{C}$ (Group 14, Period 2), $\mathrm{Al}$ (Group 13, Period 3), and $\mathrm{Ca}$ (Group 2, Period 4).
Comparing the magnitudes of electron gain enthalpy:
1. $\mathrm{F}$ has the highest negative electron gain enthalpy among these due to its small size and high effective nuclear charge, although it is slightly less than $\mathrm{Cl}$ due to inter-electronic repulsion.
2. $\mathrm{O}$ follows $\mathrm{F}$ in the same period.
3. $\mathrm{C}$ has a lower negative electron gain enthalpy than $\mathrm{O}$.
4. $\mathrm{Al}$ is a metal with a low tendency to gain electrons, but it is more electronegative than $\mathrm{Ca}$.
5. $\mathrm{Ca}$ is an alkaline earth metal with a stable $ns^2$ configuration, making its electron gain enthalpy very low (near zero or positive).
The order of magnitude of negative electron gain enthalpy is $\mathrm{F} > \mathrm{O} > \mathrm{C} > \mathrm{Al} > \mathrm{Ca}$.
Answer: $\mathrm{F}>\mathrm{O}>\mathrm{C}>\mathrm{Al}>\mathrm{Ca}$
The elements given are $\mathrm{F}$ (Group 17, Period 2), $\mathrm{O}$ (Group 16, Period 2), $\mathrm{C}$ (Group 14, Period 2), $\mathrm{Al}$ (Group 13, Period 3), and $\mathrm{Ca}$ (Group 2, Period 4).
Comparing the magnitudes of electron gain enthalpy:
1. $\mathrm{F}$ has the highest negative electron gain enthalpy among these due to its small size and high effective nuclear charge, although it is slightly less than $\mathrm{Cl}$ due to inter-electronic repulsion.
2. $\mathrm{O}$ follows $\mathrm{F}$ in the same period.
3. $\mathrm{C}$ has a lower negative electron gain enthalpy than $\mathrm{O}$.
4. $\mathrm{Al}$ is a metal with a low tendency to gain electrons, but it is more electronegative than $\mathrm{Ca}$.
5. $\mathrm{Ca}$ is an alkaline earth metal with a stable $ns^2$ configuration, making its electron gain enthalpy very low (near zero or positive).
The order of magnitude of negative electron gain enthalpy is $\mathrm{F} > \mathrm{O} > \mathrm{C} > \mathrm{Al} > \mathrm{Ca}$.
Answer: $\mathrm{F}>\mathrm{O}>\mathrm{C}>\mathrm{Al}>\mathrm{Ca}$
Hence, the correct answer is option: 'C'.