Which Element Has Similar Properties to Lithium
Magnesium and lithium of main group IA are located diagonally in the periodic table, showing a diagonal similarity.
The similarity between the properties of an element in the periodic table and the properties of another element on the upper left or lower right of it is called the diagonal rule. This similarity is more obvious between the three pairs of elements lithium and magnesium, beryllium and aluminum, boron and silicon.
The diagonal rule can be roughly explained from the viewpoint of ionic polarization of the similarities of properties between magnesium and lithium: the similarity in properties of elements on the diagonal is due to their similar ionic polarization forces. The magnitude of the ion polarizing force depends on its radius, charge and structure. For example, although lithium ions and sodium ions are in the same family and have the same ion charge, the former has a smaller radius, so its polarizing force is much stronger than that of Na+, so the properties of lithium compounds and sodium compounds are quite different. Since Mg 2+ has a higher charge and a smaller radius than sodium ions, its polarizing force is close to that of lithium ions, so Mg 2+ shows similarities in properties with the lithium ions on the upper left. It can be seen that the diagonal relationship is a concrete manifestation of the internal relationship between the structure and properties of matter.