The equations giving the response of a slightly ionized plasma with monatomic components to sinusoidal perturbations are formulated. Included in the model equations are the electron Hall effect, electron thermal diffusion, radiation and electron-atom rate processes. Plasma conditions are limited to those where viscous effects, the induced magnetic field, ion slip and atom-atom inelastic processes can be neglected. The limiting cases of frozen and equilibrium electron excited state populations are discussed. Presented are results of calculations for MHD generators with a working fluid of potassium seeded argon and with a Boltzmann distribution of electron quantum states of the seed in steady state.