Electron affinity is characterized as the energy given off when one mole of atoms in the gaseous state each absorbs one (or more) electrons to come to be a mole that anions in the gas state.
Simply put, electron affinity speak you what the energetic get is as soon as an atom i do not care an anion.
Now, let"s take a look in ~ the two factors you"ve mentioned and see exactly how they influence electron affinity.
You deserve to think of one atom"s electron affinity together a measure up of the attraction the exists between the nucleus, i m sorry is positively charged, and also the electron, which is negative charged.
This indicates that components that have tendency to reduce this attraction will additionally reduce electron affinity.
An increase in atom size leader to a decrease in electron affinity due to the fact that the just arrived electron is included further away native the nucleus, i.e. ~ above a greater energy level.
As you go down a group, the outermost electron are situated further and further far from the nucleus. This indicates that they feeling less pull coming native the nucleus. (Screening plays crucial role here, too).
If this is the case, the gain in power when one electron is added to the atom will not it is in as far-ranging #-># electron affinity decreases.
On the various other hand, one increase in effective atom charge has the precise opposite effect.
The effective atom charge is a measure up of the traction exerted on the electrons by the nucleus. In essence, that relates to an increase in atomic number, i.e. The variety of protons in the nucleus, that"s unbalanced by an increase in atomic size.
When girlfriend add much more protons to the nucleus, the will lure electrons more. If those electrons are added at the very same distance indigenous this increasingly an effective nucleus, climate they will "feel" an ext and much more pull from it.
When friend go across a duration of the periodic table, atom number increases, however electrons room being added to the same power level.
This way that an just arrived electron will be more attracted to the nucleus, which indicates that the energy gain once it is included to the atom will be more significant #-># electron affinity increases.
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That is why the regular trend in electron affinity look at the way it does.
Now, don"t be cheat by the negative sign! A more negative energy per mole means that more energy is offered off once the atom add to an electron, for this reason electron affinity increases!