The atomic number of oxygen is 8. This number represents the number of protons found in the nucleus of an oxygen atom, determining its identity as an element. Oxygen is essential for life on Earth, as it is a key component of cellular respiration in organisms, allowing them to convert food into energy. It exists naturally as a diatomic molecule (O2), which makes up about 21% of the Earth's atmosphere. The atomic structure of oxygen also enables it to form compounds with various elements, contributing to the formation of water and organic molecules, crucial for sustaining life.