Arranged the elements in order of their masses. (Today it is Relative Atomic Mass)
In 1863, suggested the elements were to be arranged in octaves --> Similar to music; the eighth note resembles the first note. Thus, there was a systematic relationship between the order of atomic masses and the repetition of their properties.
He did not leave spaces- thinking that all the elements had been found.
The law was best applied to Calcium but some were too heavy to fit Newland's idea.
In 1869 he published his table- elements were arranged by increasing atomic mass.
Why he was accepted:
Mendeleev had left spaces for elements he knew hadn't been invented yet. However, he predicted their properties and after the discovery of these unknown elements between 1874 and 1885 because Mendeleev was so close to the actual value, thats why he was accepted! Furthermore, because he predicted their properties, he was known as the father of the elements :) x