Question

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

Answer 1

(a) Element X (atomic number 17) belongs to p-block. Period 3, Group 17.

Electronic configuration of X: 2, 8, 7

Valence shell electrons = 7

So, Group number = 17

Period to which the elements belongs = 3

Element Y (atomic number 20) belongs to s-block. Period 4, Group 2.

Electronic configuration of Y:2, 8, 8, 2

Valence shell electrons = 2

So, Group number = 2

Period to which the belongs = 4

(b) X has 7 valence electrons so, it needs 1 more electron to complete its octet and Y has 2 valence electrons so it will give its 2 electrons to acquire octet configuration. Hence X will gain 1 electron and Y will lose 2 electrons, so the chemical reaction is:

X₂ + Y → YX₂

Specifically, X = Cl and Y = Ca

So, Cl₂ + Ca → CaCl₂