Electron gain enthalpy generally becomes more negative across a period as we move from left to right.
Electron gain enthalpy of an element is the energy released when a neutral isolated gaseous atom accepts an extra electron to form the gaseous negative Ion, i.e. anion. The electron gain enthalpy of an element is a measure of the firmness or strength with which an extra electron is bound.
- Halogens have the highest negative value of electron gain enthalpy.
- Energy is released when an electron is added to the atom. Therefore, the electron gain enthalpy is negative.
- Noble gases have large positive electron gain enthalpy. This is because the extra electron is placed in the next higher principal quantum energy levels.
- As we move down a group, both the atomic size and the nuclear charge increases. But the effect of the increase in atomic size is much more pronounced than the nuclear charge.
- With the increase in atomic size, the attraction of the nucleus for the incoming electron decreases.