The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7 electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. configuration of the atoms of B and D and the molecular formula of the compound formed when B and D combine.



Group number = 

  • 10 + number of valence electrons for p block elements 
  • group number = number of valence electrons for s block elements.
  A B C D
Number of Valence electrons 1 3 5 7
Group Number 1 (10+3)=13 (10+5)=15 (10+7)=17

The electronic configuration of:

  • B will be 2, 8, 3
  • D will be 2, 8, 7


Compound formed when B and D combine:

B has a valency of 3 whereas C has a valency of 1. 

Reaction of B with D - Teachoo.jpg

So, the compound formed by B and D will be BD 3

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo