Question

Which is larger in size Cs+ or Cl- ?

Answer 1

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?

 

Answer 2

Cs is an element of group 1 and period 6 and Cl is an element of group 17 and period 3.

Cs+ will match the electronic configuration of Xe which is an element of group 18 and period 5.

Cl- will match the electronic configuration of Ar which is an element of group 18 and period 3.

And we know that while we move down the group the number of shells increases. Therefore, the size of elements also increases.

Hence the size of Cs+ > Cl-

But this is the expected relationship because experimentally the radius of Cl- > Cs+

This might be because of electron--electron repulsion.


Hope it helps!!!!