Question

Why is oxygen written as ${\mathrm{O}}_2$?

Answer 1

Molecules

• Molecules are a group of atoms bound together, constituting the smallest fundamental unit of a chemical compound that may take part in a chemical process.
• On the basis of atomicity, molecules can be categorized.
• Monatomic atoms include $\mathrm{He},\mathrm{Ne},\mathrm{Ar},\mathrm{and}\mathrm{Kr}$ (all noble gases are monatomic).
• Diatomic - made up of two atoms, such as ${\mathrm{H}}_2,{\mathrm{N}}_2,{\mathrm{O}}_2,{\mathrm{F}}_2,\mathrm{and}{\mathrm{Cl}}_2$.
• Triatomic - made up of three atoms, such as ${\mathrm{O}}_3$.

Oxygen write as ${\mathbf{O}}_{\mathbf{2}}$

• The electronic configuration of ${\mathbf{O}}_{\mathbf{2}}$is $1s^{2}2s^{2}2p^4$.
• It accepts two electrons to achieve 8 electrons in its outermost shell to complete the octet as shown in the diagram given below:-
• So, the valency of oxygen is 2.
• The type of bond present between oxygen molecules is a covalent bond.
• 
• So, Oxygen is considered a diatomic molecule.
• Each molecule consists of two oxygen atoms linked together.
• Hence, its molecular formula is ${\mathrm{O}}_2$.​