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  • Which of the following has the lowest ionisation potential value?Option: 1 KOption: 2 Rb</p

Which of the following has the lowest ionisation potential value?

Option: 1

K


Option: 2

Rb


Option: 3

Cs


Option: 4

Fr


Answers (1)

best_answer

As we learned

 

Variation of I.E. down the group -

 

The number of inner electrons increases with the addition of new shells thereby the screening effect increases. Hence I.E. should decrease.

-

 

 Cs has lowest IE even though it is placed above Fr as Fr has 4f & 5f fully filled orbitals which have least shielding effect. So,

Francium has a slightly higher ionization energy than cesium, 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for cesium, as would be expected from relativistic effects, and this would imply that cesium is the less electronegative of the two.

A greater positive charge density in the nucleus for the larger atom (and higher atomic number) means higher velocity for (here) the 7s electron, which has a higher relativistic mass and thus stays closer to the nucleus than in the case of Cs 

Cs has lower IP than Fr, Rb & K

Posted by

Rishi

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