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.