An analysis of the temporal evolution of the electron energy distribution function (EEDF) and the electron swarm parameters in oxygen and chlorine gases is presented. The spatially homogeneous time-dependent Boltzmann equation is solved for dc and radio-frequency ac electric fields by a finite-element method. A comparison is made of the swarm parameters obtained for the following three cases: (a) under the actual ac field; (b) assuming that the EEDF follows faithfully the applied ac field [quasi-steady-state (QSS) approximation]; and (c) using an ‘‘effective’’ dc field (effective dc approximation). It is shown that the effective dc approximation is not applicable to either oxygen or chlorine for frequencies <10 MHz; however, the QSS approximation is justified for chlorine discharges at <13.56 MHz. This has important implications for reducing the computation time in modeling the bulk plasma of glow discharge reactors. It is also shown that atomic chlorine resulting from molecular dissociation has a significant effect on the swarm parameters, especially for large degrees of gas dissociation.