(n+l) Rule-sequence of filling subshell

subshell

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Subshell

(n+l) rule

•     The Sequence of the filling of various sub-shells may also be determined from (n+l) rule

  “The electron comes in the vacant sub-shell with lowest value of (n+l). If the value of (n+l) is same, then electron enters the sub-shell having lowest value of n.”

  n=no. of shell

  l= sub-shell s,p,d,f

  values of l for s,p,d,f subshells is 0,1,2 & 3 respectively.

  Question1. Which sub-shell is filled first 4f or 6s?

  Ans.     For 4f sub-shell,           n=4,     l=3

  n+l=4+3=7

  For 6s sub-shell            n=6, l=0

  n+l=6+0=6

  The value of (n+l) is less for 6s, So 6s is filled first

  Question2.Which sub-shell is filled first 4p or 5s?

  Ans.     for 4p sub-shell n=4, l=1

  n+l= 4+1=5

  for 5s sub-shell n=5, l=0

  n+l= 5+0=5

  Since the value of (n+l) is same for both subshells.

  4p is filled first because value of n is smaller.

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