Respuesta :
Explanation:
When energy is released by the molecules of a substance in a reaction then it is known as an exothermic reaction. And, a reaction in which heat energy is absorbed by the molecules of a substance is known as an endothermic reaction.
When we move from top to bottom in a group of periodic table then there will occur an increase in atomic radius of the elements. This also means that the number of protons and electrons also increases on moving from top to bottom.
Also, for an exothermic reaction,
[tex]E^{+}(g) + e^{-} \rightarrow E(g) + Energy[/tex]
where, E = any atom
Since, Al, Na and Rb are all metals so, they will readily lose electrons in order to attain stability. On the other hand, Cl and I are non-metals so, they will readily gain electrons in order to become stable anions in nature.
As the size of chlorine is smaller than iodine. So, chlorine will not easily lose an electron hence, it will have high electron affinity.
Also, when an electron is added to a gaseous isolated atom then then energy released is known as electron gain enthalpy.
Thus, we can conclude that electron gain enthalpy name is given to the energy for the reaction.
