Question

3. The 1st ionization energy of group 1 elements are shown below. Element IE1 (eV) 5.2 Na 5.1 4.3 Rb Cs Fr Element 119 4.2 3.9 4.1 4.9 (calculated) (a) (2 points) Rationalize the decrease observed on moving from Li to Cs. b) (2 points) Rationalize the increase observed on moving from Cs to Element 119.

Answer 1

Ams. Down the group number of shells increases which causes the outermost electron to be far away from nucleus lie the distance between nucleus and outermost election increases and hence lower value of effective nuclear charge experienced by outermast electron Hence it is easier to remove anos electron as we move down the group. So I decreases on moving down from li to Cs. Ane while moving from co to element lig., the inner shell containe completely filled do and f-orbitals . As d- and f-orbitals have poor shielding effect; they can not shield the ow attraction of nucleus on outermost electron. Hence owermost election feel more attraction (Zeff) and it become difficult to remove them. So IE increases from as to element 11g.