Question

An element 'X' forms an oxide with a formula ${{X}_{2}}{{O}_{3}}$. State the valency of 'X' and write the formula of its chloride.

Answer 1

To solve this question we first need to know what is valency. The capacity of an element to combine with other atoms to form molecules or chemical compounds is known as valency.
The electrons which are present in the outermost shell of an atom are known as valence electrons. These are the electrons that participate in molecule or chemical bond formation.

Complete answer:
The atomic number of oxygen (O) atoms is 8. Let us look at the electronic configuration of the oxygen (O) atom.
$_{8}O=1{{s}^{2}}2{{s}^{2}}2{{p}^{4}}$
From the electronic configuration, we can see that the oxygen (O) atom has 6 electrons in its outermost or valence shell.
Hence the valency of oxygen is 2. Or we can say that an oxygen (O) atom can form 2 bonds with other atoms.
So, according to the criss-cross method, we can say that the valency of element 'X' is 3.
Now, the valency of chlorine is 1.
So, element 'X' will form the molecule $XC{{l}_{3}}$ with chlorine element.
It can be assumed that the element 'X' shows a positive valency or has an oxidation state +3 since both oxygen and chlorine have negative oxidation states.

Note:
It should be noted that the element 'X' belongs to the boron group or group 13 of the modern periodic table as they form trivalent oxides. Hence the elements (boron, aluminum, gallium, indium, thallium) form covalent bonds with three oxygen atoms.