Question

An element X (atomic number 17) combines with an element. Y (atomic number 20) to form a compound.
(i) Write the positions of these elements in the modern periodic table.
(ii) Write the formula of the compound formed. Justify your answer in each case.

Answer 1

(i) The electronic configurations of the two elements are :
X (Z = 17) 2, 8, 7 , Y (Z = 20) 2, 8, 8, 2
Element X is present in group 17 (halogen family) since it has 7 valence electrons. Element Y is placed in group 2
(alkaline earth family) since it has 2 valence electrons.
(ii) Element Y is a metal with valency 2 while element X is a non-metal with valency 1. Therefore, the two combine to form compound `YX_(2).`