Tell about the difference of inner and outer transition elements in detail.
The Transition Metals are the elements found between the Group IIA elements and the Group IIB elements in the periodic table. The Group IIB are sometimes considered transition elements. The outer transition elements are also known as the d-block elements, because while the outermost level contains at most two electrons, their next to outermost main levels have incompletely filled d sub-orbitals, which are filled-up progressively on going across the periodic table from 8 to 18 electrons. The filling of the d sub-orbitals of the transition elements across a row of the periodic table is not always regular. The inner transition elements are two series of elements known as the lanthanoids (previously called lanthanides) and actinoids (previously called actinides). They are usually shown below all the other elements in the standard view of the periodic table, but they really belong to periods 6 and 7. The lanthanoid series consists of the 14 elements Cerium through Lutetium (atomic numbers 58–71), which immediately follow Lanthanum. Likewise, the actinoid series consists of the 14 elements Thorium through Lawrencium (atomic numbers 90–103), which immediately follow Actinium. These elements were among the last to be discovered and placed in the periodic table. Many of the actinoids do not occur naturally but were synthesized through nuclear reactions.