Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a “rare-earth element”.Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element.
The most important uses of yttrium are LEDs and phosphors, particularly the red phosphors in television set cathode ray tube displays. However, due to the lanthanide contraction, it is also less electronegative than its successor in the group, lutetium.Yttrium is the first d-block element in the fifth period.
The pure element is relatively stable in air in bulk form, due to passivation of a protective oxide film that forms on the surface. This film can reach a thickness of 10 µm when yttrium is heated to 750 °C in water vapor.
Yttrium is also used in the production of electrodes, electrolytes, electronic filters, lasers, superconductors, various medical applications, and tracing various materials to enhance their properties./source