Q.Describe the formation of HF molecule by orbital overlap.

Fluorine's electronic configuration leaves one half-filled 2p orbital; this orbital overlaps end-to-end (head-on) with hydrogen's half-filled 1s orbital, and the shared electron pair in this overlap region forms the H-F sigma covalent bond.

Electronic configurations:

H: 1s1 — one half-filled 1s orbital, containing one unpaired electron.

F: 1s2 2s2 2p5 — the 2p subshell has 5 electrons in three 2p orbitals (2px2 2py2 2pz1, by convention), so exactly one 2p orbital (say 2pz) is half-filled with one unpaired electron; the rest are already fully paired.

According to valence bond theory, a covalent bond forms when two atomic orbitals, each containing a single unpaired electron with opposite spins, overlap. Here, the half-filled 1s orbital of hydrogen overlaps along the internuclear axis (head-on / axial overlap) with the half-filled 2pz orbital of fluorine.

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