Alexandre-Émile Béguyer de Chancourtois was a French geologist and mineralogist who was the first to arrange the chemical elements in order of atomic weights, doing so in 1862.

Döbereiner recognised triads of elements with chemically similar properties, such as lithium, sodium and potassium, and showed that the properties of the middle element could be predicted from the properties of the other two 

And that the mean of the mass of the 1st and the 3rd element was approximately equal to the mass of the middle element.

He found that every eight elements had similar properties and called this the law of octaves. He arranged the elements in eight groups but left no gaps for undiscovered elements

Mendeleev claimed the famous periodic law that “Element properties are a periodic function of their atomic weight.” 

In his table, the Properties of elements in a period show regular gradation

It had several advantages, he left space for the new elements which would be found in the future but also predicted their properties.

In 1913 he used self-built equipment to prove that every element's identity is uniquely determined by the number of protons it has. His discovery revealed the true basis of the periodic table and enabled Moseley to predict confidently the existence of four new chemical elements, all of which were found.

He also gave the Modern periodic law which states that "properties of elements are a periodic function of their atomic number."