Abstract The adiabatic bond-charge model is extended to describe phonon dispersion curves and elastic properties in A 3 B 5 semiconductors. Asymmetry of the bond-charge position and of the force constants involving them is found to be the main consequence of ionicity. A six-parameter model provides a good fit to the experimental data for GaAs, GaSb and InSb. A small seventh parameter describing weak second-neighbor interactions is needed in GaP. Trends in the force-constant parameters are discussed.