Platinum Group

platinum group, six metals, in order of increasing atomic weight, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). The elements all possess a silvery white colour—except osmium, which is bluish white. The chemical behaviour of these metals is paradoxical in that they are highly resistant to attack by most chemical reagents yet, employed as catalysts, readily accelerate or control the rate of many oxidation, reduction, and hydrogenation reactions.

Ruthenium and osmium crystallize in the hexagonal close-packed system, and the others have face-centred cubic structures. This is reflected in the greater hardness of ruthenium and osmium.