We have studied the growth of Gd on a W(110) substrate at submonolayer coverages by means of scanning tunneling microscopy (STM). Gd forms domains of equidistant chains along the [11̄0] direction of the substrate. The distance between the chains decreases in discrete steps with increasing coverage. These chain-like superstructures coincide with the appearance of (n × 2) LEED-patterns (n = 10, 8, 7, 6, 5). Atomically resolved STM images support an earlier model which explains the chains by periodic adsorption in on-top and non-top sites. The apparent corrugation of the chains exhibits a strong bias dependence which can be explained by adsorption-site-dependent local electronic properties. Spatially resolved spectroscopy of the local barrier height is in excellent qualitative agreement with earlier spatially averaging experiments.