The key difference between Mendeleev and Modern periodic table is that the basis of the modern periodic table is mainly the electronic configuration of the elements, which we call as the atomic number whereas, in Mendeleev periodic table, it is the atomic mass of the elements.
Let us see here what is Mendeleev periodic table and what is a modern periodic table, and then compare both to understand the difference between Mendeleev and modern periodic table. Mendeleev is the pioneer of the modern periodic table, after a numerous number of changes 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 like today.
CONTENTS
1. Overview and Key Difference
2. What is Mendeleev Periodic Table
3. What is Modern Periodic Table
4. Side by Side Comparison – Mendeleev vs Modern Periodic Table in Tabular Form
5. Summary
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 have similar properties. He referred to the peculiar relationship as the “law of octaves”. However, we cannot make his law for the elements beyond Calcium. Therefore, the scientific community did not accept it.
Figure 01: Mendeleev Periodic Table
Compared to the Newland’s classification, Mendeleev’s classification system has a great improvement for two reasons. The 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 undiscovered-elements. For example, Mendeleev proposed the existence of an unknown element called eka-aluminum and predicted a number of its properties. (Eka-Meaning in Sanskrit is ‘first’. Thus eka-aluminum is the first element in the aluminum group). When scientists discovered gallium after four years, its properties remarkably matched the predicted properties of eka-aluminum.
Thus, to mention these would be as follows;
In Mendeleev periodic table, 66 elements are there. By 1900, another 30 elements scientists added to the list, filling some of the empty spaces in the table.
What is Modern Periodic Table?
The modern periodic table considers the outermost ground-state electron configuration of the elements. According to the type of subshell that fills with electrons, we can divide the elements into categories; the representative elements, noble gases, the transition elements (or transition metals) and the actinides. The representative elements are (we call them 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.
Figure 02: Modern Periodic Table
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 incomplete f-orbitals.
What is the Difference Between Mendeleev and Modern Periodic Table?
Mendeleev periodic table is the basis for the modern periodic table that we use today. It has 65 known elements, but with the newly discovered elements, there are 103 elements in the modern periodic table. The key difference between Mendeleev and Modern periodic table is that the basis of the modern periodic table is mainly the electronic configuration of the elements, which we call as the atomic number whereas Mendeleev periodic table considers the atomic mass of the elements.
The below infographic tabulates the difference between Mendeleev and Modern periodic table in detail.
Summary – Mendeleev vs Modern Periodic Table
The elements with similar chemical and physical properties recur at definite intervals in the modern periodic table, and it has 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 undiscovered elements. He also assumed the periodic variation of properties in elements. The key difference between Mendeleev and Modern periodic table is that the basis of the modern periodic table is mainly the electronic configuration of the elements, which we call as the atomic number whereas Mendeleev periodic table considers the atomic mass of the elements.
Reference:
1. Libretexts. “3.1: Mendeleev’s Periodic Table.” Chemistry LibreTexts, Libretexts, 14 Oct. 2016. Available here
2. “Periodic Table.” Wikipedia, Wikimedia Foundation, 7 Oct. 2018. Available here
Image Courtesy:
1.”Periodic table by Mendeleev, 1871″By NikNaks – Own work, (Public Domain) via Commons Wikimedia
2.”Simple Periodic Table Chart-en”By Offnfopt – Own work, (Public Domain) via Commons Wikimedia