June 19, 2021, 12:10:48 AM
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Topic: Relative Ionic Radii (K+ vs Sr2+)  (Read 350 times)

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Offline RH111

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Relative Ionic Radii (K+ vs Sr2+)
« on: April 16, 2021, 05:07:36 PM »
Hi all,

I was wondering why the potassium ion (K+) is larger than the strontium ion (Sr2+). From my understanding, the addition of the n=4 electron shell should result in the strontium ion being larger. However, that is not the case. I think the difference has something to do with the additional two protons in strontium 2+ relative to it's nearest noble gas Kr (K+ only has one additional proton commpared to Ar).

However, without searching up the atomic radii (or anything outside of what's in the periodic table), how can I compare the radii of two ions with different charges like K+ and Sr2+?

Thanks!

Offline Orcio_Dojek

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Re: Relative Ionic Radii (K+ vs Sr2+)
« Reply #1 on: April 16, 2021, 05:42:22 PM »
https://en.wikipedia.org/wiki/Atomic_radius

Quote
factor - nuclear charge - attractive force acting on electrons by protons in nucleus - increase along each period (left to right) - decreases the atomic radius

Positive charge will even increase this factor in favour of Sr2+.

Offline RH111

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Re: Relative Ionic Radii (K+ vs Sr2+)
« Reply #2 on: April 16, 2021, 05:57:14 PM »
Thanks!

A quick follow-up:
Why doesn't the same hold true for Ca2+ vs Na+ (Na+ is smaller) or Ba2+ vs Rb+ (Rb+ is smaller)?


Offline Orcio_Dojek

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Re: Relative Ionic Radii (K+ vs Sr2+)
« Reply #3 on: April 16, 2021, 06:07:17 PM »
https://en.wikipedia.org/wiki/Ionic_radius

Here they wrote tha Ca2+ is smaller than Na+ and Ba2+ is smaller than Rb+.

Offline RH111

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Re: Relative Ionic Radii (K+ vs Sr2+)
« Reply #4 on: April 16, 2021, 06:13:02 PM »
Oh, my apologies, I am mistaken. Thank you.

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