Question

The correct decreasing order of negative electron gain enthalpy for C, Ca, Al, F and O is

• A. F $>$ O $>$ C $>$ Al $>$ Ca
• B. Ca $>$ Al $>$ O $>$ F $>$ C
• C. Al $>$ F $>$ Ca $>$ C $>$ O
• D. F $>$ C $>$ O $>$ Ca $>$ Al

Hint:

Halogens and electronegative elements have the most negative electron gain enthalpy. The trend generally decreases as you move down a group and across a period.

Answer 1

The Correct Option is A

To determine the correct decreasing order of negative electron gain enthalpy for the elements C, Ca, Al, F, and O, let's analyze the concept of electron gain enthalpy.

Electron gain enthalpy is the energy change that occurs when an electron is added to a neutral atom in the gaseous state. A more negative value indicates a higher tendency to gain an electron.

Analysis of the Elements:

• Fluorine (F): Has the highest electron gain enthalpy, as it is highly electronegative and readily accepts an electron to attain a stable electronic configuration.
• Oxygen (O): Has a high negative electron gain enthalpy but not as high as fluorine due to slightly less electronegativity.
• Carbon (C): Has less tendency to gain an electron compared to oxygen but more than aluminum and calcium due to its smaller size and relatively higher electronegativity.
• Aluminum (Al): Being a metal, has a lower electron gain enthalpy compared to nonmetals like carbon, but higher than calcium.
• Calcium (Ca): As an alkaline earth metal, it showcases the least tendency to gain an electron due to its larger size and low electronegativity.

Based on these observations, the correct decreasing order of negative electron gain enthalpy is:

F > O > C > Al > Ca

Answer 2

Electron gain enthalpy refers to the energy released when an electron is added to a neutral atom in the gas phase. The more negative the electron gain enthalpy, the more likely the atom is to accept an electron. Let's analyze the trend for the elements: 

- Fluorine (F) has the most negative electron gain enthalpy because it is a halogen and easily accepts electrons to complete its octet. 
- Oxygen (O) also has a highly negative electron gain enthalpy, being an electronegative element but slightly less than fluorine due to its larger size.
- Carbon (C) has a moderate electron gain enthalpy, as it is less electronegative than oxygen and fluorine. 
- Aluminium (Al) has a less negative electron gain enthalpy than carbon due to its larger atomic radius and lower electronegativity. 
- Calcium (Ca) has the least negative electron gain enthalpy, as it is an alkaline earth metal and less likely to gain electrons. 

Thus, the correct order is F $>$ O $>$ C $>$ Al $>$ Ca.