Provide an example of the exothermic and endothermic electron affinity.

Exothermic electron affinity occurs when energy is released during the addition of an electron to an atom.

An example of exothermic electron affinity is the addition of an electron to a chlorine atom. Chlorine has seven valence electrons and requires one more to complete its octet. When an electron is added to a chlorine atom, energy is released in the form of heat. This is because the electron is attracted to the positively charged nucleus of the atom, and as it gets closer, the potential energy of the system decreases. The energy released is equal to the electron affinity of chlorine, which is -349 kJ/mol.

Endothermic electron affinity occurs when energy is absorbed during the addition of an electron to an atom. An example of endothermic electron affinity is the addition of an electron to a helium atom. Helium has two valence electrons and does not require any more to complete its octet. When an electron is added to a helium atom, energy must be supplied to overcome the repulsion between the negatively charged electron and the existing electrons in the atom. The energy absorbed is equal to the electron affinity of helium, which is +20 kJ/mol.

In summary, exothermic electron affinity occurs when energy is released during the addition of an electron to an atom, while endothermic electron affinity occurs when energy is absorbed. The electron affinity of an atom is a measure of the energy change that occurs when an electron is added to the atom, and can be either positive or negative.