Four elements P, Q, R and S belong to the third period of the Modern Periodic Table and have respectively 1,3,5 and 7 electrons in their outermost shells. Write the electronic configurations of Q and R and determine their valencies. Write the molecular formula of the compound formed when P and S combine.

Four elements P, Q, R and S belong to the third period of the Modern P

1.	Four elements P, Q, R and S belong to the third period of the Modern Periodic Table and have respectively 1,3,5 and 7 electrons in their outermost shells. Write the electronic configurations of Q and R and determine their valencies. Write the molecular formula of the compound formed when P and S combine.
Answer» Solution :Electronic configuration of Q = 2, 8,3 VALENCY of Q = 3 Electronic Configuration of R = 2,8, 5 Valency of R = 8-5 = 3 Electronic configuration of P = 2,8,1 Electronic configuration of S = 2, 8, 7 FORMULA : PS/Nacl