The second-harmonic response of single-crystal silver electrodes to an incident wavelength of 1064 nm was measured in the presence of adsorbed chloride and bromide ions. The adsorbate markedly affects the magnitude and phase of the isotropic part of the signal. In particular, the structural transitions in the adsorbed layer can be detected; transitions to dense layers are often indicated by a drop in the phase of the signal. For the case of Ag(111), we have obtained the Rudnick and Stern parameter alpha, which characterizes the electronic response perpendicular to the surface. These optical measurements were supplemented by impedance spectroscopy.