Question
How does electronic configuration vary down a group in the modern periodic table?

Answer

  • As we move from top to bottom in a group, a new shell gets added successively in the atom of an element. Therefore, the last electron enters in a new shell down the group.
  • Hence, the general outer electronic configuration of the elements in a group remains the same. This holds true for groups 1, 2 and 3 elements.
  • In the groups 13 to 18 the appropriate inner ‘d’ and ‘f’ subshells are completely filled and the general outer electronic configuration is the same down the groups 13 to 18.
  • However, in the groups 4 to 12, the ‘d’ and ‘f subshells are introduced at a later stage (4th period for ‘d’ and 6th period for ‘f’) down the group. As a result, variation in the general outer configuration is introduced only at the
Group numberGeneral outer configurationExamples
Group 1$ns ^{ 1 }$${ }_3 Li : 2 s ^{1},{ }_{11} Na : 3 s ^1$
Group 2$ns ^2$${ }_4 Be : 2 s ^2,{ }_{12} Mg : 3 s ^2$
Group 3$ns ^2( n -1) d ^{1}$${ }_{21} Sc : 4 s ^2 3 d ^{ l },{ }_{39} Y : 5 s ^2 4 d ^1$
Group 13$ns ^2 np^I$${ }_5 B : 2 s ^2 2 p ^1,{ }_{13} A 1: 3 s ^2 3 p ^1$
Group 14$ns ^2 np ^2$${ }_6 C : 2 s ^2 2 p ^2,{ }_{14} Si : 3 s ^2 3 p ^2$
Group 15$n s^2 n p^3$${ }_7 N : 2 s ^2 2 p ^3,{ }_{15} P : 3 s ^2 3 p ^3$
Group 16$ns ^2 n p^4$${ }_8 O : 2 s ^2 2 p ^4,{ }_{16} S : 3 s ^2 3 p ^4$
Group 17$n s^2 n p^5$${ }_9 F : 2 s ^2 2 p ^5,{ }_{17} C 1: 3 s ^2 3 p ^5$
Group 18 Mal$ns ^2 np ^6$${ }_{10} Ne : 2 s^2 2 p^6,{ }_{18} Ar : 3 s^2 3 p^6$

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