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Chemistry: Comparing Ionic Radii of Cs+ and Cl- ions


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Hi, given that Cs+ has 55 protons and electronic configuration of 2.8.18.18.8, and Cl- has 17 protons and electronic configuration of 2.8.8, why is the ionic radii of Cl- (0.181nm) > ionic radii of Cs+ (0.167nm)?

 

I know that Cs+ has many more protons than Cl-, which means that the pulling force on the electrons in Cs+ is much greater than that on those in Cl-, but what about Cs+ having many more layers of electrons than Cl-? Which has more significance in determining ionic radii, the pulling force on electrons, or the number of layers of electrons?

 

Is there a 'sure' way to determine whether Cs+ or Cl- (or any two ions in different groups and periods, for the matter), has the higher ionic radius?

 

Thanks in advance :)

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The ionic charge has the biggest influence since excess of electrons will cause the outer ones to be held loosely and a shortage will cause the remaining electrons to be held much more tightly. Next greatest influence is the number of layers, then the number of protons.

 

Cs+ has a smaller ionic diameter because its possitive charge and the Cl- negative charge together override the other considerations.

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The ionic charge has the biggest influence since excess of electrons will cause the outer ones to be held loosely and a shortage will cause the remaining electrons to be held much more tightly. Next greatest influence is the number of layers, then the number of protons.

 

Cs+ has a smaller ionic diameter because its possitive charge and the Cl- negative charge together override the other considerations.

 

Hi cypress, thanks for your reply! I am still slightly confused though... If ionic charge is the biggest influence, why then does Cs+ have a larger ionic diameter than F-?

 

 

 

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Hi cypress, thanks for your reply! I am still slightly confused though... If ionic charge is the biggest influence, why then does Cs+ have a larger ionic diameter than F-?

 

Fluorine has one fewer set of orbitals so now four fewer verses chlorine's three fewer. Although the effect of orbitals is less than the effect of ionic charges, eventually with enough of a difference anything will win out. With enough of them, ants can run you out of your home, right?

 

I think studying one of these diagrams is a good way to better understand the patterns of behavior you are discovering.

 

table10-9.jpg

 

Realize that these are patterns of chemic behaviors based on many chemic laws but these patterns of behaviors are not the laws themselves. There are several competing laws in play with chemic behaviors. Laws are consistent but when competing laws are in play then you get patterns that are generally but not always consistent. Try to make a distinction between observations that are based on a single or non competing chemic law or property and patterns of characteristics such as ionic radius.

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