Shweta thakur Asked a Question
March 8, 2021 7:54 pmpts 30 pts
55. fve One electron cntc (2=39) and ends at cadil filling of 5p-orbilals starts at indium (2 The sixth period corresponds to the fillin filling of sixth energy level, i.e., n eriod corresponas to the fillin O. 4f. five 5d and three 6p) are availabl for filling with electrons, therefore Seen onbitals (one 6s, seven 4 sLth period contain.s thirty-two ele 6s-orbital and ends up with radon (Z = 86) in wh after the filling of 6s-orbital, the next electro and thereafter, the filling of seven , Se ents. It begins with caesium (Z= 55) in which one clectron enters the = 55) in which one electron enters the don (Z = 86) in which the filling of 6p-orbitals is complete. In this period. lectron (i.e., 57th) enters the d- orbital against the aufbau principle 4f-orbitals begins with cerium (Z= 58) and ends up with lutetium hehaviour can be explained on the basis of greater stability of the xenon (inert gas) core. This anomalous behaviour can be should occur in 4f-orbital jn accordance with 56). the addition of the next electron (i.e., 57th) should occur in 4f-orbital in accordance with inle This will, however, tend to destabil1ze the xenon core (Z=54, [Kr] 4d 4f 5s 5psd) since After barium (Z= 56), the additi refore, the 57th electron prefers to enter 5d-orbital which lies outside the the 4-orbitals lie inside the core. There xenon core and whose energy 1s only slightly ince 0se energy is only slightly higher than that of 4f-orbital. In doing so, the stability conferred on the atom due to xenon core more than compensates the slight instability caused by the addition of one electron To the higher energy 5d-orbital instead of the lower energy 4-orbital. Thus, the outer electronic configuration of the lower energy 4f-orbital. Thus, the outer electronic configuration of La (7-57) is Sd' 6s rather than the expected 4" 6s. Once Sd-orbital has one electron, the next electron (Le, 58th enters the inner 4f-orbital (instead of the outer 5d-orbital) due togreater nuclear charge Thus, the outer electronic configuration of Ce (Z= 58) is 4f 5d' 6s. The next electron (i.e., S9thy not only goes to 4f-subsholl but also pulls back the single 5d-clectron to 4f-subshell (making it f) due to greater nuclear charge. Thus, the outer electronic configuration of Pr (Z= 59) is 4f° 5d 6s. Thereafter, the regular filling of 4f-orbitals occurs till they are completely half-filled at Eu (Z = 63, 4f 5d 6s). The next electron (i.e., 64th) as expected does not go to 4f-subshell but goes to 3d-subshell due to greater stability of the exactly half-filled 4f-orbitals. Thus, the outer electronic contiguration 0f gadolinium is 4f 5d6s. The next electron (i.e., 65th) not only goes to 4f-subshell but also pulls back the SIngie Sd-electron to 4fsubshell, thereby making it 4f9 5d0, i.e., the outer electronic configuration of Tb (Z=03) 6. Thereafter, the continuous regular filling of the 4/-subshell occurs till it is complete at TO o). Ihe next electron (i.e., 71) as expected goes to the higher energy 5d-orbital thereby compicng u 1anthanide series at lutetium (Z= 71, 4f 5d 6s).
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  • Priyanshu kumar Best Answer
    The 5d orientation gives the atom less unfilled filled subshells and hence most stability. You must be knowing that an atom does whatever it takes to be stable.
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    Shweta thakur
    yes sir ...sir the electronic configuration of f block elemants are quite different .... although I read and got a bit idea about lanthanoid electronic configuration but confused i...
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