How do ionization energy and electron affinity determine whether atoms of elements will combine to form ionic compounds?
Let us consider the definitions of ionisation energy and electron affinity for a moment.
(First) ionisation energy - The minimum amount of energy required to remove the most loosely bound electron from an isolated gaseous atom to form an ion with a
Electron affinity - The amount of energy absorbed when an electron is added to an isolated gaseous atom to form an ion with a
Note, then, that these two values (which are constants for each element) are NOT simply reverses of each other :
#"EF"_1"( reversed ) : ""X" ^+(g) + e^(-) -> "X"(g)#
#"EA: " "X"(g) + e^(-) -> "X" ^(-) (g)#
This demonstrates that first ionisation energy determines the tendency of an atom to loose its most loosely bound electron to become a
Thus, a low first ionisation energy means that very little energy is required to remove that electron from the atom, and so means that the atom forms its
Thus, it is now easy to see how ionisation energy and electron affinity affect the likelihood of ionic bonding taking place, by having an impact on the tendency of cation and anion formation.