Anomaly of lithium
The periodicity of Group IA is very obvious, but lithium is still very different from other alkali metal elements of the same family. This difference is mainly manifested in the covalence of lithium compounds, which is caused by the small atomic radius of lithium.
Diagonal rule
In the periodic table of elements, alkali lithium has some similarities with alkaline earth magnesium (Mg) at its diagonal position, which reflects the "diagonal rule" locally existing in the periodic table of elements. The similarities between lithium and magnesium are as follows:
(1) Normal oxide is generated by the interaction of simple substance and oxygen
(2) The simple substance can be directly combined with nitrogen (other alkali metal simple substances of the same family as lithium have no such property)
(3) Fluoride, carbonate and phosphate are insoluble in water
(4) Carbonate is easy to decompose when heated
The reason is that the lithium magnesium diagonal rule can be explained by the change of ion radius in the periodic table. In the same period, from left to right, the ion radius decreases with the increase of effective charge, and the ion radius of the same group elements increases from top to bottom with the increase of the number of electronic layers. Because lithium and magnesium are at the diagonal, magnesium is just at the "bottom right" of lithium, and its ion radius decreases with the gradual change of the period, and increases with the gradual change of the family, Similarity appears after the two offset
