What is electron affinity and how it depends on atomic size, effective nuclear charge and screening factor?

Electron affinity is a measure of the energy change that occurs when an electron is added to a neutral atom to form a negative ion. In other words, it is the energy released (or absorbed) when an electron is added to an atom in its gaseous state.

The electron affinity of an atom depends on several factors, including:

Atomic Size: Generally, as the atomic size increases, the electron affinity decreases. This is because larger atoms have electrons that are farther from the nucleus, so there is less of an electrostatic attraction between the nucleus and the incoming electron. As a result, it becomes easier to add an electron to a larger atom, leading to a lower electron affinity.

Effective Nuclear Charge: The effective nuclear charge is the net positive charge experienced by an electron in an atom. It takes into account the shielding effect of inner electrons. As the effective nuclear charge increases (i.e., more protons in the nucleus), the attraction between the nucleus and the incoming electron becomes stronger, resulting in a higher electron affinity.

Screening Factor: The screening effect, also known as shielding, occurs when inner electrons repel outer electrons, thereby reducing the net attraction felt by the outer electrons toward the nucleus. If there is effective screening by inner electrons, the outer electrons experience less attraction to the nucleus, leading to a lower electron affinity.

In summary, larger atoms tend to have lower electron affinities because their outer electrons are farther from the nucleus and experience weaker attraction. At the same time, higher effective nuclear charge and weaker screening lead to higher electron affinities due to stronger attraction between the nucleus and the incoming electron.