The lanthanide elements from lanthanum to lutetium inclusive are incorporated into the body of the periodic table. They are subdivided into three sub-groups according to their important oxidation states: La to Sm, Eu to Tm, Yb and Lu, so that Eu and Yb fall directly below Ba; La, Gd, Lu form a column directly below Y; Ce and Tb fall in a vertical line between Zr and Hf. Pm falls below Tc; both are radioactive, and not naturally occurring. The elements (...) with easily attained 2+ and 4+ oxidation states are grouped and clearly differentiated. Gadolinium has an important position as the centre of four triads in the block of elements that surround it– La, Gd, Lu; Ba, Gd, Hf; Eu, Gd, Tb; Yb, Gd, Ce. This new arrangement has the advantages of compactness, simplicity and clarity – there are no tie lines; and important oxidation states of these metals are emphasized. The actinides are also accommodated within this system, and element 114 falls naturally below lead in Group 14. (shrink)

The periodic table of the elements is one of the most powerful icons in science: a single document that captures the essence of chemistry in an elegant pattern. Indeed, nothing quite like it exists in biology or physics, or any other branch of science, for that matter. One sees periodic tables everywhere: in industrial labs, workshops, academic labs, and of course, lecture halls. It is sometimes said that chemistry has no deep ideas, unlike physics, which can boast quantum mechanics and (...) relativity, and biology, which has produced the theory of evolution. This view is mistaken, however, since there are in fact two big ideas in chemistry. They are chemical periodicity and chemical bonding, and they are deeply interconnected. The observation that certain elements prefer to combine with specific kinds of elements prompted early chemists to classify the elements in tables of chemical affinity. Later these tables would lead, somewhat indirectly, to the discovery of the periodic system, perhaps the biggest idea in the whole of chemistry. Indeed, periodic tables arose partly through the attempts by Dimitri Mendeleev and numerous others to make sense of the way in which particular elements enter into chemical bonding. (shrink)