Chapter 19.1, Problem 7R

To determine

To explain: oxygen must be written as ${\text{O}}_{\text{2}}$ in a chemical equation.

Explanation of Solution

Introduction:

The chemical formula is a way of describing any chemical substance using the representation of its elements.

The atomic number of oxygen is 8. Oxygen atom is very reactive in nature. This can’t exist as pure oxygen, because of the reactive nature of the oxygen atom. Therefore, two atoms of oxygen combine to form an oxygen molecule $\left({\text{O}}_{\text{2}}\right)$ . This is why oxygen gas is written as $\left({\text{O}}_{\text{2}}\right)$ in a chemical formula.

Conclusion:

Hence, due to the reactive nature of oxygen, oxygen gas is written as $\left({\text{O}}_{\text{2}}\right)$ .