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.
Elements in the lanthanide and actinide series are often considered to be inner transition metals. The transition metals are identifiable in the periodic table below as peach, the inner transition metals are dark pink and light pink in color. The d block transition metals are in columns 3-12 (often labeled 1B-10B in other versions of the periodic table). The f block inner transition metals are in the two long rows below the periodic table. Inner transition metals are often just referred to as transition metals.