Question

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

(i) Write the position 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 position of elements X in the modern periodic table is group number 17 and period number 3. The position of element Y in the modern periodic table is group number 2 and period number 4. Electronic configuration of element X = 2, 8,7.

It has 3 shells so period number 3.

Halogens are kept in group 17.

Electronic configuration of element Y = 2,8,8,2

It has 4 shells so a period number is 4.

The valence shell has 2 electrons so the group number is 2.

(ii) The formula of the compound:

Valency of element Y =2

Valency of element X=1

YX₂