A sigma molecular orbital is a type of molecular orbital that is formed by the overlap of atomic orbitals along the internuclear axis. It is a bonding orbital and is typically represented by the Greek letter sigma (σ).
A sigma molecular orbital is formed by the head-to-head or tail-to-tail overlap of atomic orbitals, while a pi molecular orbital is formed by the sideways overlap of atomic orbitals. Additionally, sigma molecular orbitals are typically lower in energy and have a greater contribution to the overall bond strength compared to pi molecular orbitals.
No, not every molecule has a sigma molecular orbital. This is because not all molecules have atomic orbitals that are aligned along the internuclear axis for the formation of a sigma bond. Some molecules only have pi bonds or no bonds at all.
In the case of B2, both atoms have a half-filled 2pz atomic orbital, which allows for the formation of a sigma molecular orbital through head-to-head overlap. This contributes to the stability of the molecule and its ability to form strong bonds with other atoms.
Yes, a molecule can have multiple sigma molecular orbitals. The number of sigma molecular orbitals depends on the number of atomic orbitals involved in the bonding process. For example, a molecule with two bonding atoms can have two sigma molecular orbitals, one formed by the overlap of the 2s orbitals and one formed by the overlap of the 2p orbitals.