Writethe electronicconfigurationof element withatomicnumbers89and 90and predictwhetherthey ared- orf- blockelements .

Writethe electronicconfigurationof element withatomicnumbers89and 90an

1.	Writethe electronicconfigurationof element withatomicnumbers89and 90and predictwhetherthey ared- orf- blockelements .
Answer» Solution :Electronicconfigurationof Rn (Z =86) is`[Xe]^(54)4f^(14)5d^(10)6s^(2)6p^(6)` Afterfilling6p- subshellfilling 7S- subshellstartsat Fr (Z= 87)= `[Rn]^(86)7s^(1)` and iscompleteat Ra `(z=88)= [Rn]^(86)7s^(2). ` Thereforethe fillingof 5f- subshellshould beginin ACCORDANCEWITH aufbauprinciple. But DUETO (i) stillsmallerenergydifference between5f- and 6d- orbitalsthan between4f- and5d- orbitalsand (ii)greaterstabilityof theradon core thenexttwo electrons(i.e.,89 thand 90 th)afterthefilling of 7s- orbitalsprefer to enter 6d- orbitalsbeforefillingthe 5f- ORBITALS. Thusthe electronicconfigurationare : `Ac (Z=89)= [ Rn]^(86)7s^(2)6d^(1)` andThe `(Z= 90)= [Rn ] ^(86)7s^(2)6d^(2)` Hereagain theyshould becalledd- blockelementsbut arecalledf-blockelements becausethe INNER 5f- orbitalsare stillempty.