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.
The inner transition metals are shown in two rows at the bottom, in pink and purple. An inner transition metal is one of a group of chemical elements on the periodic table. They are normally shown in two rows below all of the other elements. They include elements 57-71 (lanthanides) and 89-103 (actinides). The lanthanides are very similar, and the actinides are all radioactive. They have three incomplete outermost electron shells and are all metals.