Earlier when periodic table was not there scientist face problem to arrange the elements.
When scientist discovered more elements they saw that there are elements who posses same characteristics.So, they started arranging elements with same properties together.
Arranging elements together helps to predict the characteristics of the element .
Mendeleev's arrange the periodic elements according to atomic mass of element.
Then comes Moseley which arranges element on the basis of atomic number.
Well, when it was first created, the person who created it (Dmitri Mendeleev?) sorted it in a way that he noticed there were some missing elements. Through the organization by atomic number and other information, he hypothesized the existence of undiscovered elements and he was eventually found to be right. Other than that, it helps with finding out how chemical bonds work and with which elements they work best with, as well as showing correlations with electronegativity, groups, etc.
