Formation of Hydrogen, Fluorine, Hydrogen Fluoride and Oxygen Molecules

Formation of hydrogen (H₂). Hydrogen's electronic configuration is 1s¹. When two hydrogen atoms combine, the 1s orbital of each (each containing one unpaired electron, of opposite spin to the other) overlaps with the other along the internuclear axis -- an s-s overlap. Being axial, this overlap forms a σ-covalent bond (Fig 10.18).

Formation of fluorine (F₂). Fluorine's valence-shell configuration is 2s² 2pₓ² 2p_y² 2p_z¹ -- only the 2p_z orbital is half-filled. When the half-filled 2p_z orbitals of two fluorine atoms overlap along the z-axis (the molecular axis here), a p-p overlap results, forming a σ-covalent bond between the two fluorines (Fig 10.19).

Formation of hydrogen fluoride (HF). Hydrogen's configuration is 1s¹; fluorine's valence-shell configuration is again 2s² 2pₓ² 2p_y² 2p_z¹. When hydrogen's half-filled 1s orbital overlaps LINEARLY with fluorine's half-filled 2p_z orbital, an s-p overlap forms the σ-covalent H-F bond (Fig 10.20).

Formation of oxygen (O₂). Oxygen's valence-shell configuration is 2s² 2pₓ² 2p_y¹ 2p_z¹ -- TWO half-filled orbitals (2p_y and 2p_z) per atom. Taking the internuclear (z) axis as the molecular axis: the half-filled 2p_z orbitals of the two oxygens overlap head-on along that axis, forming a σ bond; the half-filled 2p_y orbitals of the two oxygens, being parallel to each other but perpendicular to the molecular axis, overlap SIDEWAYS, forming a π bond (Fig 10.21). Together, this one σ bond plus one π bond give the O=O double bond in dioxygen. The remaining, already-paired 2s and 2pₓ electrons on each oxygen do not participate in bonding and remain as lone pairs. …