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### Topic: Why do smaller ions tend to be more strongly hydrated?  (Read 8229 times)

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#### tdod

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##### Why do smaller ions tend to be more strongly hydrated?
« on: July 28, 2012, 09:49:37 PM »
Why do smaller ions tend to be more strongly hydrated? For instance, why is Mg2+ expected to be more strongly hydrated than Be2+?

I looked in my textbook, but their explanation isn't helpful making sense to me:
Quote
The smaller ions presumably are able to bind the hydrating water molecules more firmly and thus show a more negative value for ∆S˚solution

But if this is true, then wouldn't smaller ions have weaker hydration, since they don't negative ∆S leads to positive ∆G

Thanks!

#### Dan

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##### Re: Why do smaller ions tend to be more strongly hydrated?
« Reply #1 on: July 29, 2012, 05:38:50 AM »
Think about how ionic radius affects ΔH, I think this is the dominant effect.
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#### XGen

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##### Re: Why do smaller ions tend to be more strongly hydrated?
« Reply #2 on: July 29, 2012, 10:29:45 PM »
I believe it has something to do with how much attraction a smaller ion can exert compared to a larger ion.

#### mugabo daniel

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##### Re: Why do smaller ions tend to be more strongly hydrated?
« Reply #3 on: August 11, 2012, 12:34:47 PM »
also try to look at the diagonal relationships of magnesium and lithium.
i also think that due to a small ionic radius there exists a strong attraction of the lone pairs of electrons of the water molecules by the nucleus of the ion.

#### manonemission

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##### Re: Why do smaller ions tend to be more strongly hydrated?
« Reply #4 on: August 18, 2012, 09:06:23 AM »
Could it be related to the way that more distant electrons in larger atoms require less energy to excite them to a higher level and thus form 'conduction bands?'

#### MrTeo

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##### Re: Why do smaller ions tend to be more strongly hydrated?
« Reply #5 on: August 20, 2012, 03:39:14 AM »
Could it be related to the way that more distant electrons in larger atoms require less energy to excite them to a higher level and thus form 'conduction bands?'

Er... No, I think it's much easier than that.
Just think about two spheres with different radii and the same charge on them, you will easily find out that the smaller one has the largest electric field on its surface. As we can roughly consider dominant the electrostatic interactions in the hydration process the charge/radius ratio (which is in fact the E field, if we neglect some constants) is directly linked to the strength of these forces...
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