It’s dependent on whether it’s either ionised or not, as well as the type of oxygen it is, O2 molecule or atomic oxygen. One oxygen atom that is not ionized molecules contain 8 electrons, which are split between two layers two and six. This means that the second layer isn’t filled and can accommodate two electrons, which is the reason for the preference for forming two oxygen atoms molecules.GCSE CHEMISTRY Covalent Bonding within an Oxygen Molecule What is the structure of the Oxygen Molecule? — GCSE Science.