Molecular orbitals sigma and pi are types of molecular orbitals that describe the distribution of electrons within a molecule. Sigma orbitals are formed by the head-to-head overlap of atomic orbitals, while pi orbitals are formed by the side-to-side overlap of atomic orbitals.
Sigma orbitals are typically lower in energy and more stable than pi orbitals. They also have a cylindrical symmetry along the internuclear axis. In contrast, pi orbitals have a nodal plane perpendicular to the internuclear axis, resulting in a dumbbell shape.
Sigma orbitals are typically involved in single bonds, such as the sigma bond in a C-C single bond. Pi orbitals, on the other hand, are involved in double and triple bonds, such as the pi bonds in a C=C double bond or a C≡C triple bond.
The formation of sigma and pi bonds leads to increased electron density between atoms, resulting in a more stable molecule. This is due to the lowering of the overall energy of the system as electrons occupy these molecular orbitals.
Yes, sigma and pi orbitals can overlap simultaneously in a molecule. This can occur in molecules with multiple bonds, such as in the case of a double bond where there is both a sigma and a pi bond between the same two atoms.