An element ' X ' has its electronic configuration in outer most shell is ( a − 5 ) s 2 and total number of electrons in its outermost, penultimate and antipenultimate shell are 2, 8 and 25 r

Question

An element ' X ' has its electronic configuration in outer most shell is ( a − 5 ) s 2 and total number of electrons in its outermost, penultimate and antipenultimate shell are 2, 8 and 25 respectively then find out total number of unpaired electrons in element 'X' in their ground state (where 'a' is number of p electrons in chlorine atom in ground state).

TestHub · Accepted Answer

Value of a : Chlorine ( Z = 17 ) has the configuration 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 , giving a = 6 + 5 = 11 total p -electrons. Outermost shell ( n = 6 ): Configured as ( a − 5 ) s 2 = 6 s 2 , which contains 2 electrons. Penultimate shell ( n = 5 ): Contains 8 electrons, completely filling the 5 s 2 5 p 6 subshells. Antipenultimate shell ( n = 4 ): Contains 25 electrons, distributed as 4 s 2 4 p 6 4 d 10 4 f 7 (since 2 + 6 + 10 + 7 = 25 ). Unpaired electrons: The only partially filled subshell is 4 f 7 . According to Hund's rule, all 7 electrons occupy separate orbitals singly. Final Answer: The total number of unpaired electrons in element 'X' is 7.

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