An oxygen atom is a basic unit of matter that makes up the element oxygen, which is essential for life on Earth. It consists of eight protons in its nucleus, surrounded by eight electrons that orbit the nucleus in energy levels. The number of protons defines the element, making oxygen unique among other elements. Oxygen is represented by the chemical symbol O and has an atomic number of 8. It is a vital component of the atmosphere, making up about 21% of the air we breathe. Oxygen is crucial for processes like cellular respiration, where it helps organisms convert food into energy.