**Electron Gain Enthalpy**

Electron gain enthalpy refers to the energy change that occurs when an atom gains an electron to form a negatively charged ion. It can be either exothermic (releasing energy) or endothermic (absorbing energy) depending on various factors.

**Factors Affecting Electron Gain Enthalpy**

1. Atomic Size: The size of the atom plays a crucial role in determining the electron gain enthalpy. Generally, smaller atoms have a higher electron gain enthalpy as the added electron experiences a stronger attraction from the positively charged nucleus.

2. Nuclear Charge: The greater the nuclear charge, the stronger the attractive force on the incoming electron. As a result, atoms with a higher nuclear charge tend to have a more exothermic electron gain enthalpy.

3. Electron Configuration: The electron configuration of an atom determines its stability. If an atom already has a stable electron configuration, it will require more energy to add an electron, making the electron gain enthalpy endothermic. On the other hand, if the atom has an incomplete or unstable electron configuration, it will readily accept an electron, leading to an exothermic electron gain enthalpy.

4. Electron-electron Repulsion: Electrons are negatively charged particles and tend to repel each other. When an additional electron is added to an atom, it experiences repulsion from the already present electrons. This repulsion leads to an increase in energy, making the electron gain enthalpy endothermic.

**Ionization Enthalpy**

Ionization enthalpy refers to the energy required to remove an electron from a neutral atom to form a positively charged ion. It is always endothermic due to the following reasons:

1. Attraction of Nucleus: The electron is held by the attractive force of the nucleus. Removing an electron requires overcoming this force, which requires energy input.

2. Repulsion between Electrons: Electrons repel each other due to their negative charges. As a result, removing an electron from an atom decreases the electron-electron repulsion, leading to a decrease in potential energy. This decrease in potential energy corresponds to an increase in energy required, making the ionization enthalpy endothermic.

3. Stability of the Atom: Removing an electron disrupts the stability of the atom as it alters the electron configuration. This disruption requires energy input, resulting in an endothermic process.

In conclusion, the electron gain enthalpy can be either exothermic or endothermic depending on factors such as atomic size, nuclear charge, electron configuration, and electron-electron repulsion. On the other hand, the ionization enthalpy is always endothermic due to the attractive force of the nucleus, electron-electron repulsion, and the disruption of atom stability.