What is electron affinity and how does it relate to the periodic table?

Electron affinity is the energy released when an atom gains an electron.

Electron affinity is a measure of how strongly an atom attracts additional electrons. It is defined as the energy released when an atom gains an electron. This energy is negative because the process is exothermic. The greater the electron affinity, the more energy is released when an electron is added.

Electron affinity varies across the periodic table. Generally, electron affinity increases from left to right across a period and decreases from top to bottom within a group. This trend can be explained by the effective nuclear charge, which increases across a period and decreases down a group. Atoms with a higher effective nuclear charge have a stronger attraction for electrons and therefore a higher electron affinity.

There are some exceptions to this trend, however. For example, the electron affinity of group 2 elements is lower than expected because their outermost electrons are in an s orbital, which is farther from the nucleus and shielded by the inner electrons. Additionally, the electron affinity of group 15 elements is lower than expected because adding an electron would result in a half-filled p orbital, which is less stable than a full or empty orbital.

In summary, electron affinity is a measure of an atom's attraction for additional electrons. It varies across the periodic table due to differences in effective nuclear charge and orbital stability.