All noble gases have positive electron gain enthalpy where trend in decreasing order is:

A. \(He\)

B. \(Ne\)

C. \(Ar\)

D. \(Kr\)

E. \(Xe\)

Choose the correct answer from the options given below:

\(Ne > Ar \approx Kr > Xe > He\)

The correct answer is option 2. \(Ne > Ar \approx Kr > Xe > He\).

Electron gain enthalpy (or electron affinity) is the amount of energy released or absorbed when an electron is added to a neutral atom in the gas phase. For noble gases, this value is typically positive because these elements already have a stable electronic configuration, and adding an electron would require placing it in a higher energy level, which is less favorable.

Trends in Electron Gain Enthalpy Among Noble Gases:

General Trends:

As you move down the noble gas group from Neon (Ne) to Radon (Rn), the atomic size increases. A larger atomic size means that the added electron would be farther from the nucleus, experiencing less attractive force from the nucleus and more repulsion from the existing electron cloud. Larger atoms also have more electron-electron repulsion in the outer shells. Adding an extra electron increases this repulsion, making it less favorable.

Specific Noble Gases Trends:

Neon (Ne): Neon is the smallest noble gas with a high positive electron gain enthalpy. This is because the added electron is relatively close to the nucleus, where the effective nuclear charge is high and repulsion is minimal. Thus, adding an electron to neon is less unfavorable compared to other noble gases.

Argon (Ar) and Krypton (Kr): Both have similar electron gain enthalpies because they are of similar size. The added electron is in a more distant orbital compared to neon, so the electron gain enthalpy is less positive due to increased repulsion and decreased effective nuclear charge.

Xenon (Xe): Xenon is much larger than Argon and Krypton, so the electron gain enthalpy is even lower (more positive) because the electron being added is even further from the nucleus and experiences significant repulsion.

Helium (He): Despite being the smallest noble gas, Helium has a relatively low positive electron gain enthalpy. This is due to the very small size and high repulsion from the already filled first shell. Adding an electron would require placing it into a higher energy level, which is highly unfavorable.

Thus, the electron gain enthalpy of noble gases decreases in the order: Ne > Ar ≈ Kr > Xe > He.