Group 18 consists of elements: helium, neon, argon, krypton, xenon, radon and oganesson. All these are gases and chemically unreactive. They form very few compounds, because of this they are termed as noble gases. All noble gases have general electronic configuration ns²np⁶ except helium which has 1s². Many of the properties of noble gases including their inactive nature are ascribed to their closed shell structures. Due to stable electronic configuration these gases exhibit very high ionization enthalpy. However, it decreases down the group with increase in atomic size. Atomic radii increase down the group with increase in atomic number. Since noble gases have stable electronic configurations, they have no tendency to accept the electron and therefore, have large positive values of electron gain enthalpy.

What is the electron gain enthalpy for noble gases?

> 0

The correct answer is option 1. > 0.

Noble gases are known for their inertness, meaning they rarely participate in chemical reactions. This inertness is due to their electron configuration. Here's why electron gain enthalpy for noble gases is positive:

Full valence shell: Noble gas atoms have their outermost electron shell completely filled. This full shell provides a very stable electronic configuration, minimizing the atom's desire to gain or lose electrons.

Adding an electron disrupts stability: If a noble gas atom were to gain an electron, it would have to be placed in a higher energy level orbital further from the nucleus. This disrupts the stable arrangement and requires energy input.

Positive electron gain enthalpy: Electron gain enthalpy (EGE) represents the energy change when an atom gains an electron. Since adding an electron to a noble gas requires energy input, the EGE value for them is positive.

Imagine a perfectly balanced ball on a platform. Adding another ball (electron) disrupts the balance and requires pushing it upwards (energy input) to find a new stable position.

While EGE is positive for all noble gases, it becomes slightly less positive down the group (He to Rn). This is because the increasing size of the atom weakens the attraction between the nucleus and the outermost electrons, making them slightly more receptive to an extra electron.