Low-temperature scanning tunneling microscopy at $7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is used to assemble monatomic native adatom chains on a Cu(111) surface and to study their $sp$-derived quantum states. The adatoms within the structure reside on equivalent nearest-neighbor lattice sites of the substrate surface (intrinsic Cu-Cu spacing $2.55\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$). Starting from linear chain segments, kinked chains and triple-terminal junctions are created, and the impact of the different structural details of the junction on the electronic properties is investigated by spectroscopic measurements. A simple tight-binding (TB) parametrization scheme is applied to discuss the experimentally observed energies and densities of the quantum states inherent to these chain structures of advanced complexity. The TB model also reveals potential overlaps of resonance-broadened states, which are not resolved in the experiment.