Tin needs four electrons to fill its 5p orbital and can form compounds with four covalent bonds. Alternatively, tin can lose two or four electrons to form Sn2+ or Sn4+ ions, respectively. Tin is element number 50 on the periodic table. Its ground state electron configuration is [Kr]4d105s25p2.
Although tin has a completely full 4d orbital, most sources classify it as a transition metal. In nature, relatively little tin can be found as a free element. Instead, most occurs as tin dioxide, or SnO2, in the ore cassiterite. Some tin is found in an alloy called stannine, with the chemical formula Cu2FeSnS4. Important tin alloys include bronze, which is 80 percent copper and 20 percent tin, and solder, which is 67 percent lead and 33 percent tin.