The molecular orbital theory explains the bonding in the HF (hydrogen fluoride) molecule through the combination of atomic orbitals from the hydrogen and fluorine atoms to form molecular orbitals.
In HF, we primarily consider the atomic orbitals of hydrogen (1s) and fluorine (2p). When these atomic orbitals overlap, they create two types of molecular orbitals: bonding and antibonding orbitals. The bonding orbital is lower in energy and is formed from the constructive interference of the atomic orbitals. This stabilization leads to an increase in electron density between the two nuclei, which helps to hold the atoms together.
Specifically, the bonding in HF occurs when the hydrogen’s 1s orbital merges with one of fluorine’s 2p orbitals (often the 2pz), creating a lower energy molecular orbital that is occupied by the shared pair of electrons. This electron sharing leads to a strong covalent bond between the hydrogen and fluorine atoms.
Moreover, the electronegativity difference between hydrogen and fluorine creates a dipole moment, which, according to molecular orbital theory, can also be described in terms of the varying extent of electron sharing and the distribution of electron density in the bonding orbital. As a result, this model not only accounts for the bond formation but also explains the molecular polarity of HF.