Electron Affinity reflects the ability of an atom to accept an electron.
It is the energy change which occurs when an electron is added to a gaseous atom. Atoms with strong effective nuclear charge have greater electron affinity.
The reaction occurs when an atom recieves an electron can be shown in representation as :
X + e− → X− + energy
Similarly, another way to define is as the amount of energy that is needs to be present to remove an electron from a singly charged negative ion:
X− → X + e−
Electron affinity is the amount of energy to detach one electron, from a negatively charged ion of an atom or molecule. It is indicates the usage of the symbol Ea and is usually express in units of kJ/mol.
Properties
Electron affinity follows a particular path on the periodic table. It increases when it moves down a column or group and also shows an increase when it moves from left to right across a period or row( except for the noble gases). The value may be either positive or negative value, the negative value means energy must be present in order to attach an electron to the ion, here the capture of electrons is an endothermic process. If value is positive the process is exothermic and occurs spontaneously.
Each of these elements has a completely filled valence electron shell and an electron affinity that approaches zero.
Non-metals typically have higher value than metals. The elements Chlorine strongly attracts electrons while mercury is the element with atoms that most weakly attract an electron.
In conclusion Electron affinity is more difficult to analyse in molecules as their structure is shows complications.
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