A negative-ion, positive-ion plasma produced by the release of an electron attachment chemical into the F region becomes electrically polarized by the collisions with neutrals moving across magnetic field lines. The resulting electric field causes E¿B drift of the two ion species and the residual electrons. The cross-field flow of the modified ionosphere is computed using a two-dimensional numerical simulation which includes electron attachment and mutual neutralization chemistry, self-consistent electric fields, and three-species plasma transport. The velocity of the plasma is initially in the direction of the neutral wind because the negative-ion cloud is a Pedersen conductivity enhancement. As the positive and negative ions react, the Pedersen conductivity becomes depressed below the ambient value and the velocity of the plasma reverses direction. A plasma hole remains after the positive and negative ions have mutually neutralized. The E¿B gradient drift instability produces irregularities on the upwind edge of the hole. These processes may be observed experimentally with optical and backscatter-radar diagnostics.