Final answer:
HCl is formed through a molecular orbital interaction between H's 1s and Cl's 3pz orbitals, resulting in a sigma bond with a bond order of 1. Nonbonding orbitals on Cl, like 3px and 3py, contain lone pairs and do not affect the bond order. The orbital interaction causes polarity due to the electron density being closer to Cl.
Step-by-step explanation:
The formation of HCl through the interaction of hydrogen's 1s orbital and chlorine's 3pz orbital is explained by molecular orbital theory. The hydrogen (H) 1s atomic orbital (AO) is closest in energy to chlorine’s (Cl) 3p orbitals. When these atoms combine to form hydrochloric acid (HCl), the significant interaction is between the H 1s and Cl 3pz orbitals. This interaction results in the formation of bonding and antibonding molecular orbitals. The 3px and 3py orbitals of chlorine do not overlap significantly with the hydrogen 1s orbital and are therefore considered nonbonding molecular orbitals, which contain lone pairs of electrons that do not contribute to the bond order. The bond order of HCl is calculated as (2 - 0) ÷ 2 = 1, indicating a single sigma bond. Additionally, due to the relative energies of the orbitals involved, the bonding molecular orbital has electrons concentrated closer to the chlorine atom, which leads to the polarization of the H-Cl bond.