Difference Between Mendeleev and Modern Periodic Table

Mendeleev vs Modern Periodic Table
 

The key difference between Mendeleev and modern periodic table is that Mendeleev’s periodic table was based on the increasing atomic masses while the modern periodic table is based on the increasing atomic numbers. Let us see here what is Mendeleev periodic table and what is modern periodic table, and then compare both to understand the difference between both periodic tables. Mendeleev is the pioneer of the modern periodic table, though a numerous number of changes had been made to the old version of the periodic table. Both of these attempts are equally important to the scientific community; because without an invention of the periodic relationship in elements, the modern developments in Science would not reach a development era as today. Before the invention of Mendeleev’s classification, there were several attempts made by several chemists, but their periodic laws were inadequate to apply for all the elements. The modern periodic table is so advantageous for the development in the Science.

What is Mendeleev Periodic Table?

In 1869, a Russian chemist Dmitri Mendeleev and a German chemist Lothar Meyer proposed a tabulation of periodic elements on the basis of periodic recurrence of properties. In 1864, before Mendeleev , an English chemist John Newlands arranged the elements in order of atomic mass where every eight elements has similar properties. He referred the peculiar relationship as the law of octaves. However, this law could not be applied for the elements beyond Calcium. Therefore, it was not accepted by the scientific community.

Compared to the Newland’s classification, Mendeleev’s classification system has a great improvement for two reasons. First factor is, it grouped the elements together more accurately according to their properties. Second, it made the possible prediction of the properties of several elements that had not been discovered by that time. For example, Mendeleev proposed the existence of an unknown element called eka-aluminum and predicted number of its properties. (Eka-Meaning in Sanskrit is ‘first’, thus eka-aluminum would be the first element in the aluminum group). When gallium was discovered after four years, its properties remarkably matched the predicted properties of eka-aluminum.

Property                                     Eka-aluminum (Ea)                       Gallium (Ga)
Atomic mass                                  68 amu                                         69.9 amu
Melting point                                 Low                                                30.15 0C
Density                                           5.9 gcm-3                                       5.94 gcm-3
Formula of oxide                          Ea2O3                                             Ea2O3

In Mendeleev periodic table, there were 66 known elements. By 1900, another 30 elements were added to the list, filling some of the empty spaces in the table.

Mendeleev's Periodic Table
What is Modern Periodic Table?

The modern periodic table is considered the outermost ground-state electron configuration of the elements. According to the type of subshell being filled, the elements are divided into categories; the representative elements, noble gases, the transition elements (or transition metals) and the actinides. The representative elements are (also called main group elements) the groups in IA to 7A, which all the elements have incompletely filled s or p subshells of the highest principle quantum number. With the exception of Helium (He) all the 8A elements have filled p-subshell.

The transition metals are the elements of 1B and 3B through 8B, where molecules have incompletely filled d-subshells. The lanthanides and actinides are sometimes called f-block elements since those elements have incompletely filled f-orbitals.

Difference Between Modern Periodic Table and Mendeleev's Periodic Table

What is the difference between Mendeleev and Modern Periodic Table?

• Modern periodic table contains about 103 elements, in Mendeleev periodic table there were only about 66 elements.

• The basis of the modern periodic table is mainly the electronic configuration of the elements, we called it atomic number, whereas in Mendeleev’s time he considered the atomic mass of the elements.

• In Mendeleev periodic table, there were gaps for un-discovered elements, but modern periodic table has a uniformity.

• Both of these classifications consider the periodic relationship in properties of the elements.

• Both, Mendeleev and Modern, periodic tables are used to predict chemical and physical properties of unknown elements.

• In classification, both had arranged elements in groups or families.

Mendeleev vs Modern Periodic Table Summary

Mendeleev periodic table was based on the increasing atomic masses and the modern periodic table is based on the increasing atomic numbers. The elements with similar chemical and physical properties recur at definite intervals in the modern periodic table. In modern periodic table, there are about 103 elements. When Mendeleev classified them, there were only 66 elements in the periodic table. However, Mendeleev left places empty in his periodic table for the un-discovered elements. He also assumed the periodic variation of properties in elements.

 

Image Courtesy:

  1. Modern Periodic Table by 2012rc (CC BY 3.0)