The chemical symbol for oxygen is O. In the periodic table, oxygen is classified as a non-metal and is essential for life on Earth. It has an atomic number of 8, meaning each oxygen atom contains eight protons in its nucleus. Oxygen is a diatomic molecule (O2) in its natural state, which means it is typically found as two oxygen atoms bonded together. It plays a critical role in respiration for most living organisms and is also necessary for combustion processes, making it a vital element in both biological and chemical reactions.