# CHEM HELP ANYONE ASAP

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Arrange the members of the following set of cations in order of increasing ionic radii:

Sr2+
Ba2+
Rb+
K+
I understand that Sr2+ = 132 pm
Ba2+ = 149 pm
Rb+ = 166 pm
K+ = 152 pm

increasing ionic radii ....Sr2+ , Ba2+ , K+, Rb+
But the its not going in online as correct

• CHEM HELP ANYONE ASAP -

Where did your numbers for radius come from? They must not agree with the data base? So where do the numbers the data base is using come from?
My inclination, which doesn't agree with your numbers,
K+ is the smallest. You know Rb+ must be larger. You know Sr must be smaller than Rb so we have K^+ to Sr^2+ to Rb^+. That leaves Ba^2+ to be placed. Since that is another complete shell larger I think that must go above Rb. I would place these as
K, Sr, Rb, Ba from lowest to highest I think the ONLY way to do this, considering that ionic ion measurements are so uncertain, is to use the same system the database is using.

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