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.
Transition Elements. The transition elements are those elements having a partially filled d or f subshell in any common oxidation state. The term transition elements most commonly refers to the d-block transition elements. The 2B elements zinc, cadmium and mercury do not strictly meet the defining properties, but are usually included with the transition elements because of their similar properties.