Why is the activity series of ions in aqueous solutions ordered?

[so-crates]

Is there any reason for order the activity series of ions in aqueous solutions? For example, why is Calcium higher than sodium?

 

[Borek]

Is there any reason for order the activity series of ions in aqueous solutions? For example, why is Calcium higher than sodium?

Long ago I have a discussion on a similar subject with one of my professors at Uni. It went like this (I was answering):

Q: Why is calcium higher than sodium?
A: When you take ionization energy and hydratation energy for both ions and you calculate potentials, calcium is higher then sodium.
Q: OK, but why is calcium higher than sodium?
A: Because when you take into account the results of the quantum cacluations you get such ionization and hydratation energy, that calculated potential for calcium is higher than potential for sodium.
Q: OK, but why is calcium higher than sodium?
A: Eeee... Because that's a way it is?
Q: OK, good. Let's move to another question.

Later I have learned that "Because that's a way it is" is the answer for most chemistry questions - you may look for reasons, but the final answer is always "Because that's a way it is"

 

[so-crates]

What would the hydration energy have anything to do with it? The ions aren't reacting with hydrogen.

 

[Borek]

What would the hydration energy have anything to do with it? The ions aren't reacting with hydrogen.

OK. its hydration, not hydratation, but it has nothing to with hydrogen. Every ion in the solution is surrounded by the water particles - the are dipoles so they are electrically attracted. Amount of energy involved when the water particles are forming ordered layers is called hydration energy.