Precious metals (silver (Ag), gold (Au)) and platinum metals (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt)) are extremely nonreactive, they are very stable and can be found in nature in elementary form. Poor reactivity of these metals originates from the fact that their atoms are significantly smaller than the alkali metal atoms, so their valence electrons are much closer to the atomic nucleus and are more firmly attached to it. That is why they have higher values of the ionization energy than alkali metals.