lanthanides
Lanthanides - a group of chemical elements separated from the 6th period of the periodic table. Their unofficial common symbol is Ln. It starts with lanthanum. and ends on lutecia. It counts 15 elements: lanthanum, cerium, praseodymium, neodymium, promet, samar, europ, gadolinium, terbium, dysprosium, holm, erb, tul, iter and lutet. Lanthanides are divided into a subgroup of cerium and a subgroup of terbium. Lanthanides have very similar physical and chemical properties. These are the metals that can reach the maximum oxidation level IV, although they are most likely to occur in the III oxidation state. The ability of lanthanides to oxidize at levels II and IV is explained by the differences in the energy state of electrons at 4f, depending on their number. Electrons are most permanently associated when level 4f is half full or full, so the most stable 4f level configuration is gadolinium and lutetium. The oxidation states IV, Ce, Pr, Tb, Dy, and the oxidation degree II - Nd, Pm, Sm, Eu, Tm, Yb, ie, the roots of which the number of electrons at 4f is close to 0, 7 and 14.