The 2p orbitals combine to produce a filled sigma and two filled perpendicular pi orbitals. The remaining two electrons occupy each of the pi* anti bonding orbitals with a single electron with the same spin. This reduces the bond order to two (three bonding, one anti bonding) bond and accounts for the TRIPLET ground state of oxygen due to Hund’s rule. As the molecule has two unpaired electrons, molecular oxygen is paramagnetic.
… and two half-filled pi* orbitals and one empty antibonding sigma* orbital.
The core orbitals derived from 1s and 2s orbitals are very similar to those displayed for nitrogen.
Explore bonding orbitals in other small molecules
Hydrogen | Fluorine | Nitrogen | Hydrogen Fluoride | Carbon Monoxide | Methane | Ammonia | Ethylene | Acetylene | Allene | Formaldehyde | Benzene