Anti-Bonding Orbitals: Molecular orbitals that increase the energy of a molecule when occupied by electrons. They result from destructive interference between atomic orbitals.
Sigma Bond:A type of covalent bond where electron density is concentrated along the axis connecting two nuclei, usually formed by head-on overlapping atomic orbitals.
Pi Bond: A type of covalent bond where electron density is concentrated above and below the plane of the nuclei, usually formed by side-on overlapping p-orbitals.