Some elements and

a) BaCl₂

b) ZnO

c) 2

Valency is the combining capacity of an element. It can be treated as the number of electrons lost, gained or shared by an atom in a chemical combination.

The following are the steps to write chemical formulae from valency.

•First write the element with lower electronegativity.

•Exchange the valency of each element and write as suffix.

•Divide the suffix with common factor.

•If the suffix is 1, need not be written.

a) Ba is written first since it has lower electronegativity. The valences are exchanged and put as suffix, so Ba gets chlorine valency 1 as suffix and Cl gets barium valency 2 as suffix. Division by common factor 1 yields same. the suffix one is not needed. so, its simply written as BaCl₂.

b) Zn is written first since it has lower electronegativity. The valences are

exchanged and put as suffix, so Zn gets oxygen valency 2 as suffix and O gets zinc valency 2 as suffix. Division by common factor 2 yields Zn₁O₁. The suffix one is not needed. so, its simply written as ZnO.

c) CaO

We know that the valency of O is 2, as its given. Let’s consider the valency of Ca is x. So, by following above rules, the chemical formula should be, Ca₂O_x. But the formula of calcium oxide is CaO which can be written as Ca₁O₁. So, the suffix are divided by 2 to get Ca₁O_x/2 . Comparing Ca₁O_x/2 with Ca₁O₁ , we get that

x/2 = 1

x = 2.

Hence valency of Ca is 2.