why was Mendeleev able to predict the properties of the elements that belonged in the blanks in his table?

Question

thank u for answering

Answer 1

Because largely the properties of the elements are defined by their atomic number or the number of protons and electrons.

Also if you new the properties of a couple of the elements in a line then you could make an educated guess as to what the properties will be for the unknown element.

Answer 2

He saw that the blanks were above and/or below known elements. So based on the properties of the known elements, he predicted that others would be found with similar properties. Because he arranged the table according to atomic weights, he was able to tell what atomic weights the new elements would have.