It has long been presumed that there is a common cause at the genetic, cognitive, and neural levels for autism's characteristic triad of symptoms. However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur.
1 Transition metals are kinds of metals that have electrons in d or f orbitals. 2  Transition metals are in columns 3-12 of the periodic table and in the lanthanide and actinide series.  Most transition metals are lustrous, silvery, hard, and good conductors; however, properties may vary greatly.
Overview. Cadmium is a transition metal. The transition metals are the elements found in Rows 4 through 7 between Groups 2 and 13 in the periodic table, a chart that shows how elements are related. Cadmium was discovered by German chemist Friedrich Stromeyer (1776-1835) in 1817. It is found most commonly in ores of zinc.