The atomic number 77 is associated with the element iridium. Iridium is a chemical element in the periodic table that has an atomic number of 77 and an atomic weight of 192. It is a hard, brittle, silvery-white transition metal of the platinum group. Iridium is the second densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. It has a relatively high melting point of 2410 °C and is the only metal to maintain good mechanical properties in air at temperatures above 1600 °C.