Soon, Mendeleev was predicting the properties of three elements – gallium, scandium and germanium – that had not then been discovered. So convinced was he of the soundness of his periodic law that he left gaps for these elements in his table.

Germanium was one of the elements whose existence was predicted in 1869 by Russian chemist Dmitri Mendeleev, after he noticed a gap between silicon and tin in his periodic table. Mendeleev had predicted the new element’s density would be 5.5 g/cm3 and its atomic weight would be 70. The element in question was gallium.

Germanium was one of the elements whose existence was predicted in 1869 by Russian chemist Dmitri Mendeleev, after he noticed a gap between silicon and tin in his periodic table. Mendeleev had predicted the new element’s density would be 5.5 g/cm3 and its atomic weight would be 70.

To put some order into his study of chemical elements, Mendeleev made up a set of cards, one for each of the 63 elements known at the time. Mendeleev wrote the atomic weight and the properties of each element on a card.

Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements. The element germanium was discovered later.

Hint: Genesis of periodic classification of elements into groups and development of periodic law and the periodic table….Complete step by step solution:

What eventually happened to these gaps? Mendeleev left gaps in between his periodic tabel as he knew that no exisiting (undiscovered) element could fill the gap and that there has to be an element. The gaps were eventually filled when new elements were discovered.

There are no gaps in the periodic table. Atomic numbers of known elements go from 1 to something over 115 with no missing numbers. The atomic number tells you the number of protons in the nucleus and by extension electrons in the shell, they can only be integers. There are no gaps in the periodic table.

Disadvantages: He couldn’t allocate a correct position to hydrogen. Atomic masses didn’t increase in a regular manner, so it was impossible to predict how many elements could be discovered between two elements. Isotopes of all elements posed a problem to his periodic table.

Noble Gases

In Mendeleev’s periodic table there were gaps for undiscovered elements. Modern periodic table maintains uniformity. In Mendeleev’s periodic table noble gases were not placed (as they are not discovered at that time). In Modern periodic table noble gases in a seperate group named as group-18.

Merits and demerit of mendeleev’s periodic table

• There was a regular gradation in physical and chemical properties of elements.
• The group number of an element indicates highest oxidation state that it can attain.
• There were many vacant spaces in Mendeleev’s periodic table for the elements to be discovered.

The difference between Mendeleev and Moseley periodic table is that Mendeleev periodic table is created based on the atomic masses of chemical elements whereas Moseley periodic table is created based on the atomic numbers of chemical elements.

The modern periodic table does correct the defects of Mendeleev’s periodic table. However, it is the right places for them but is against Mendeleev’s periodic law. These elements atomic number shows the reverse order compared to atomic mass.

Lanthanides and Actinides kept separately under the table not kept within the Modern periodic table. i) It could not provide a proper plzcement of hydrogen…. ii) no place to isotopes of various elements is given….