Chemical Bonding and Hybrid Orbitals Chemical bonds can be considered the overlap of adjacent orbitals. In the case of H-Cl, the 1s orbital of H can overlap with the 3pz orbital of Cl and form a (polar) covalent bond. 1s 2p This overlap will fill both vacant orbitals of the two atoms and is called a (sigma) s- bond. In the case of CH4, we would expect it to have 3 C-H bonds identical and 1 C-H bond of differing energy because they are bonding with a different atomic orbital (C has 1 2s orbital and 3 2p orbitals available for bonding in its first excited state). In reality there are four identical bonds. This leads to the bonding theory that the s and p orbitals combine and make four identical hybrid orbitals called sp3. This bonding theory can also account for multiple bonds. In the case of formaldehyde, H , the central atom (AX3) has the \ C == O:: / H 2 bonding orbital sp . This accounts for the overlaps between the atoms but not the double bond. The bonding theory states that the extra 2pz filled orbital of carbon will have a sideways overlap with the adjacent orbital of oxygen. This is called a (pi) Π- bond. The formaldehyde structure has 3s and 1Π bond.