A chemical element, symbol Rh, atomic number 45, relative atomic weight 102.905. Rhodium is a transition metal and one of the group of platinum metals (ruthenium, osmium, rhodium, iridium, palladium, and platinum) that share similar chemical and physical properties. The gas-phase atom has the electronic configuration 1s², 2s², 2p⁶, 3s², 3p⁶, 3d¹⁰, 4s², 4p⁶, 4d⁸, 5s¹. The ionic radius for the cation Rh³⁺ is 0.0665 nanometer, and the metallic radius is 0.1345 nm.