Mendeleev takes into consideration the basic property of elements, namely, the atomic mass, as standard and arranged 63 elements known at that time in an increasing order of their atomic masses. Then, he transformed this into the periodic table of elements in accordance with the physical and chemical properties of these elements. On the basis of the law that the properties of elements are a periodic function of their atomic masses, to all the known elements, Mendeleev arranged the elements, keeping in mind that the information available till then was not final and it could change. Following this, Mendeleev’s periodic table is said to have the following merits.
1. In order to give the atoms proper place in the periodic table as per their properties, the atomic masses of some elements were revised. For example, the previously determined atomic mass of beryllium, 14.09, was modified to the correct value 9.4, and beryllium was placed before boron.
2. Mendeleev’s periodic table has vacant places to accommodate the elements that are not discovered yet. Three of these unknown elements were eka-boron, eka-aluminium and eka-silicon from the known neighbours with atomic masses 44, 68 and 72, respectively. Not only this, but their properties were also predicted. Later on, these elements were discovered and named as scandium (Sc), gallium (Ga) and germanium (Ge) respectively. The properties of these elements matched well with those predicted by Mendeleev. Due to this success, all were convinced about the importance of Mendeleev’s periodic table and this method of classification of elements was accepted immediately.
3. Meanwhile, Mendeleev’s periodic table did not have a place to include the noble gases like helium, neon or argon. But, later, in the 19th century, when they were discovered, Mendeleev created the zero group where the noble gases fitted very well without any disturbance to the original periodic table.