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In school, I learnt that Potassium is the most reactive element in the reactivity series. In the periodic table, the further you go down the more reactive the elemnt is. If this is true, then shouldn't francium be the most reactive metal? Or rubidium, or caesium? I am very confused.

Areehant Gupta
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    https://chemistry.stackexchange.com/questions/9051/why-do-the-trends-in-reactivity-not-apply-for-francium – Mithoron May 01 '22 at 22:25
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    This is not so much a question about what's more reactive; the more important part is that this reactivity series which you learn is not meant to be exhaustive, unless it literally contains every (metallic) element in the Periodic Table. Why should a reactivity series, something you learn for everyday practical use, go out of its way to include francium, an element which we can't even get significant quantities of? – orthocresol May 01 '22 at 23:44
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    Additionally, reactivity order can be different thermodynamically-wise and kinetically-wise, and is also scenario dependent. – Poutnik May 02 '22 at 09:23

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Francium is the most reactive. It cannot be pure because it can react with almost everything. I think you are using Potassium because it is the most reactive element used in most schools. Caesium and rubidium are more reactive than Potassium, but francium is even more reactive. You cannot legally use it withoutr approval from the government.

Potassium is not as dangerous as Caesium and rubidium, but you are allowed to witness it in schools with strict scientific control

Miller
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Reactivity as a metal(i.e, electropositivity) DOES increase down a group and rubidium, francium etc are more reactive.

However,the reactivity series taught in school is meant to be a stepping stone towards the rest of the reactivity series, and understanding the trends that control them. Pottassium is one of the more common metals used in chemistry and is considerably reactive, comparing to iron or copper. In many cases, the reactivity is series is not meant to be all encompassing, but a quick trick to the most common metals used.

Sarah k
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According to most schooling rules, the study of only the first 20 elements (i.e., from H to Ca) is included in the syllabus until the 10th standard, or higher; because after Calcium, the transition elements start, that have variable valency as a result of loss of electrons from the penultimate shell. Studying these elements thus becomes quite complicated. Now considering the first 20 elements, in the alkali metals, Potassium is present at the most bottom part, and is surely more reactive than either Lithium or Sodium. Hence, in our schools, it was taught that Potassium is the most reactive metal. But, considering the whole periodic table, we conclude that Francium is the most reactive. (Sometimes, it is also stated that Caesium is more reactive, because Francium is radioactive).

Rudra Gadge
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