A neutral atom of oxygen is represented as O. It has an atomic number of 8. Hence, it contains 8 electrons and 8 protons. When oxygen forms an ion, it gains 2 electrons to become a O2- ion. Oxygen gas is the most common form of oxygen known to us. In its gaseous form, each molecules of gas contains 2 atoms of oxygen and thus a total of 16 electrons.
Oxygen is an element and a member of period 2 and group 16 of the periodic table of elements. Apart from its most common application in cellular respiration (and that is why we breathe it in and the same process is the reason we breathe out carbon dioxide), there are a large number of organic compounds that contain oxygen and are of interest to us.
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