text: Yttrium is a soft, silver-metallic, lustrous and highly crystalline transition metal in group 3. As expected by periodic trends, it is less electronegative than its predecessor in the group, scandium, and less electronegative than the next member of period 5, zirconium. 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. When finely divided, however, yttrium is very unstable in air; shavings or turnings of the metal can ignite in air at temperatures exceeding 400 °C. Yttrium nitride (YN) is formed when the metal is heated to 1000 °C in nitrogen.