Elektroniväli

Elektroniväli, often translated as electron affinity, is a fundamental concept in chemistry that describes the energy change that occurs when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion. This energy change can be either exothermic, meaning energy is released, or endothermic, meaning energy is absorbed. A more negative electron affinity indicates a greater tendency for the atom or molecule to accept an electron.

The electron affinity of an element is a periodic trend. Generally, it increases across a period from left to right, as the nuclear charge increases, pulling the incoming electron more strongly. Moving down a group, electron affinity typically decreases because the additional electron is added to a higher energy level, further from the nucleus, and is shielded by inner electrons. However, there are notable exceptions to this trend, particularly for elements in the second period where electron-electron repulsions in the smaller valence shell can make accepting an additional electron less favorable than for elements in the third period.

Electron affinity is a crucial property for understanding chemical bonding, particularly the formation of ionic compounds. Elements with high electron affinities readily accept electrons, contributing to their ability to form negative ions. This property, alongside ionization energy, helps predict the type of bond that will form between elements. It is typically measured in electronvolts per atom (eV/atom) or kilojoules per mole (kJ/mol).