The oxygen molecule is often "misunderstood". The oxygen molecule is a "di-radical". The O=O notations is not adequate to describe the ground state of molecular oxygen; the correct Lewis structure would have to contain two dots to represent two unpaired electrons. In the "triplet state", the two unpaired electrons have the same spin. In the "singlet state", the two unpaired electrons have opposite spins. This triplet state corrosponds to the most stable configuration of dioxygen and the singlet state is much less stable.