Question

Identify the valency of element X in the following compounds.
(A) $X{{H}_{3}}$
(B) $XC{{l}_{5}}$
(C) ${{X}_{2}}{{O}_{3}}$
(D) $X{{O}_{2}}$

Answer 1

Hint: Valency of Hydrogen atom is 1. Chlorine atom has valency of 1. The oxygen atom’s valency is 2. To get the formula of compound, the valency of constituent atoms is crisscrossed. The crisscrossed values are reduced to the smallest possible ratio.

Complete step by step solution:
a) $X{{H}_{3}}$
Let the valency of X atom be $a$.
We know that the formula of compound is written by crisscrossing the valencies. The valency of a Hydrogen atom is 1.
Therefore,
$\left( \begin{matrix}
   X & H \\
   a & 1 \\
\end{matrix} \right)$
So, the formula becomes $X{{H}_{a}}$, comparing it with $X{{H}_{3}}$
We get $a$ as 3 so the valency of X atom is 3 in $X{{H}_{3}}$.
b) $XC{{l}_{5}}$
Let the valency of X atom be $a$.
We know that the formula of compound is written by crisscrossing the valencies. The valency of Chlorine atoms is 1.
Therefore,
$\left( \begin{matrix}
   X & Cl \\
   a & 1 \\
\end{matrix} \right)$
So, the formula becomes $XC{{l}_{a}}$, comparing it with $XC{{l}_{5}}$
We get $a$ as 5 so the valency of X atom is 5 in $XC{{l}_{5}}$.
c) ${{X}_{2}}{{O}_{3}}$
Let the valency of X atom be $a$.
We know that the formula of compound is written by crisscrossing the valencies. The valency of Oxygen is 2.
Therefore,
$\left( \begin{matrix}
   X & O \\
   a & 2 \\
\end{matrix} \right)$
So, the formula becomes ${{X}_{2}}{{O}_{a}}$, comparing it with ${{X}_{2}}{{O}_{3}}$
We get $a$ as 3 so the valency of X atom is 3 in ${{X}_{2}}{{O}_{3}}$.
d) $X{{O}_{2}}$
Let the valency of X atom be $a$.
We know that the formula of compound is written by crisscrossing the valencies. The valency of Oxygen is 2.
Therefore,
$\left( \begin{matrix}
   X & O \\
   a & 2 \\
\end{matrix} \right)$
So, the formula becomes ${{X}_{2}}{{O}_{a}}$, comparing it with $X{{O}_{2}}$
We get the ratio as 2: $a$ = 1:2 which gives us a as 4.
We get $a$ as 4 so the valency of X atom is 4 in $X{{O}_{2}}$.

Note: -Atoms having 1 valency are Sodium, Potassium, Silver and gold. Magnesium and Calcium have 2 as valency. Aluminium atom as 3 as valency. Fluorine atoms have 1 as valency.
- When a compound consists of metal and non-metal the symbol or name of metal is written first in the formula or name of the compound.