Final answer:
Valence bond theory explains the bonding in F2, HF, and ClBr by the overlap of atomic orbitals to form sigma (σ) bonds.
Step-by-step explanation:
Valence bond theory describes bonding as a consequence of the overlap of two separate atomic orbitals on different atoms that creates a region with one pair of electrons shared between the two atoms. When the orbitals overlap along an axis containing the nuclei, they form a sigma (σ) bond, which is a strong bond. When they overlap in a fashion that creates a node along this axis, they form a pi (π) bond, which is a weaker bond.