Platinum
. Platinum, symbol Pt, relatively rare, chemically inert metallic element that is more valuable than gold. The atomic number of platinum is 78. The element is one of the transition elements in group 10 (or VIIIb) of the periodic table (see Periodic Law ). Platinum is the most important of the group of elements called the platinum metals, the other members of which are ruthenium , rhodium , palladium , osmium , and iridium . Platinum metals were probably used in alloyed forms in ancient Greece and Rome and were first mentioned in European literature in the early 16th century. The separation of the other platinum metals from platinum and from each other was accomplished in the early 19th century. II PROPERTIES AND OCCURRENCE Platinum is a grayish-white metal with a hardness of 4.3. It has a high fusing point, is malleable and ductile, expands slightly upon heating, and has high electrical resistance. Chemically the metal is relatively inert and resists attack by air, water, single acids,