Explanation:

When a gas phase atom in its ground state gains an electron, it undergoes a process known as electron gain enthalpy.

Electron Gain Enthalpy:

Electron gain enthalpy is defined as the energy change that occurs when a neutral gaseous atom gains an electron to form a negative ion. It is a measure of the ability of an atom to attract and accept an electron.

Factors affecting Electron Gain Enthalpy:

The electron gain enthalpy of an atom depends on several factors:

1. Atomic size: Smaller atoms have a higher electron gain enthalpy as the incoming electron experiences a stronger attractive force from the nucleus.

2. Nuclear charge: Higher nuclear charge results in a higher electron gain enthalpy as the attractive force between the nucleus and the incoming electron is stronger.

3. Electronic configuration: If the incoming electron enters a completely filled or a stable configuration, it requires more energy to add an electron, resulting in a higher electron gain enthalpy.

4. Shielding effect: Greater shielding effect by inner electrons reduces the attraction between the nucleus and the incoming electron, leading to a lower electron gain enthalpy.

Significance:

The electron gain enthalpy is an important concept in chemistry as it helps in understanding the reactivity and chemical behavior of elements. Elements with higher electron gain enthalpy tend to have a greater affinity for electrons and are more likely to form negative ions. On the other hand, elements with lower electron gain enthalpy have a lower tendency to gain electrons and are more likely to form positive ions.

Answer:

Therefore, when a gas phase atom in its ground state gains an electron, the process is referred to as electron gain enthalpy.

The energy required to gain an electron is electron gain enthalpy. enthalpy is just another word for energy.