why does reactivity increase with decreasing ionization energy?

[Medic2MD4me]

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I can't wrap my head around this. I would expect less reactivity with lowered energies but Potassium, with a lower ionization energy is more reactive than calcium.

 

[5words]

This one is tricky, it depends on the ionization energy in question. So, we have two types of ionization energy , the first being the energy needed to remove the least tightly bonded electron from a neutral Atom; and the second is the energy required to remove the least tightly bonded electron from a Cation. And in general, the Second IE is always greater than the First.

Now reactivity can be defined as a quest for the closed valence shell ns2np6. The closer to that configuration an atom is the more reactive it will be. When you look at the periodic table, the electronic configurations of K and Ca are [Ar]4s1 and [Ar]4s2 respectively. Thus because, K can reach the closed shell configuration by losing one electron, it;s highly reactive, because atom prefer the closed-shell or noble gas configuration. Ca on the other hand, will have to lose 2 electron (so IE1 + IE2) to attain the same configuration which require lot of energy thus is less reactive. So, Lower IE = Higher reactivity.

 

[aldol16]

Why would you expect lower reactivity? Potassium has a low ionization energy, telling you that it's really easy to lose an electron. And if it's easy to lose an electron, you would expect it to be really reactive - say, to lose that electron really quickly. And that's what happens say (don't do this), if you put a chunk of potassium metal into water.

 

[Medic2MD4me]

Ok thanks! Those were helpful. It's really anxious to lose that one electron so it's reactive.