An element X (atomic number 17) reacts with an element Y (atomic number 20) to a compound.

(a) Write the position of these elements in the modern periodic table.

(b) Write the formula of the compound formed. Justify your answer in each case.

Justify your answer in each case.

(a) Since the element X has atomic number = 17. So, its electronic configuration will be 2, 8 and 7

It has 7 electrons in its outermost shell and therefore it belongs to the 10+7 th group i.e. group 17. Moreover, it has three electronic shells in total. So, it belongs to period 3.

The atomic number of element Y = 20

The electronic configuration of element Y= 2, 8, 8, 2

Now, element Y has 2 electrons in its outermost shell. So, the group number of element Y = 2. It has 4 electron shells. So, it belongs to period 4.

(b) Valency of element ‘X’ is 1

valency of element ‘Y’ is 2

‘X’ is a non metal and ‘Y’ is a metal. So, X and Y will form an ionic bond.

So, the compound formed is: YX₂