What value was there in predicting the properties for gaps in mendeleev's table?

Predicting the properties for gaps in Mendeleev’s table helps discover new elements. Because during his presentation of his proposed periodic table, he noted some gaps in his table and predicted that there are still unknown elements between those gaps. He uses some prefixes like dvi-, tri-, and eka- in order to give provisional names to his predicted elements. In his periodic table, he also laid out his elements from the lightest to the heaviest element. The lightest elements started from zero, some examples are gases.

Electron equations of the given changes are as follow,a)                              cu      →      cu⁺²  + 2e⁻b)                              mg⁺²  +  2 e⁻      →      mgc)                              cl⁻    →      cl  +  1e⁻d)                              s  +  2 e⁻    →      s²⁻e)                                o²⁻      →      o  +  2 e⁻f)                              p  +  3 e⁻    →      p³⁻g)                              fe²⁺    →      fe³⁺  + 1 e⁻h)                              s²⁻    →      s⁴⁺  +  6 e⁻