The Disadvantages of the Modern Periodic Table

Mendeleev’s periodic table gained wide acceptance from the scientific community; this has earned him credit as the discoverer of the periodic law. Element number 101, was synthesized in the year 1955, and it was named as mendelevium after the name of the founder of the periodic table. It was, however, around several years after Mendeleev died before the various complexities with the atomic masses should be explained and before the reasons behind the repetition of chemical properties could be fully explained.

Overview of the Periodic Law

When Mendeleev put forth his periodic table together, then everyone was surprised to know about the existence of the nucleus.  It was not until the year 1911 that Rutherford conducted his gold foil experiment that has helped in demonstrating the presence of the nucleus in the atom. Two years later, in 1913, English physicist Henry Moseley (1887-1915) examined x-ray spectra of a number of chemical elements. He would shoot X-rays through crystals of the element and then he studied the wavelengths of the radiation he detected.  Moseley was able to find that there was a relationship between the wavelength and atomic number. His observations led to the discovery of the definition of atomic number as the number of protons contained in the nucleus of each atom. He then believed that the elements of the periodic table must be arranged in an order of increasing atomic number rather than increasing atomic mass. 

Disadvantages of the Modern Periodic Table

• No fixed place was given to hydrogen as it resembles alkali metals as well as halogens. 

• Isotopes of the same element possess different atomic masses. Therefore each of these isotopes must be given a different position. But isotopes that were chemically similar should be given the same position. 

• At specific places, an element of higher atomic mass was placed before an element of lower mass. E.g Cobalt (Co = 58.93) is generally placed before nickel (Ni = 58.71).  

• Some elements that were placed in the same subgroup had different properties. E.g. Manganese (Mn) is placed with halogens that totally differ in the properties. 

Limitations of Modern Periodic Table

Position of hydrogen element: The position of hydrogen was not accepted in his table as some properties of hydrogen were similar to alkali metals and some were similar to halogens.

Position of isotopes: The position of isotopes was also not given accurately. Isotopes refers to atoms of the same elements, they possess the same atomic number, but varying atomic mass. Mendeleev’s table was totally based on the increasing order of atomic masses, but he assigned the same position to isotopes that possess different atomic masses rather than placing them at different positions. For example, isotopes of hydrogen occupied the same position in his table.

Presence of anomalous pairs: There were few elements that were not present in the order of their increasing atomic masses. For example, there were some pairs of elements in which an element with more atomic mass was placed before the element that has less atomic mass like that of Argon (Ar) with atomic mass 40 is placed before the Potassium (K) with atomic mass 39. Similarly, Cobalt (Co) having atomic mass 60 comes before Nickel (Ni) that has an atomic mass of 59 in his table.

Conclusion

In the year 1869, Dmitri Mendeleev discovered a method of organizing elements based on their atomic mass. His method was later revised, but it has served as a basis for the method used today. Mendeleev formulated a periodic table of all the elements that were known at that time. The rows of the table, known as the periods, each row comprised about eight elements that increased in atomic mass from left to right. The columns of the table are known as groups, it comprises the elements having similar properties. Mendeleev’s periodic table was considered as a good model since it can be used to predict the properties of unknown elements. All of these missing elements were slowly discovered. Here we come to an end of this topic, we hope that you were able to grasp a clear concept of the disadvantages of demerits of the modern periodic table, an overview of the periodic law, and also the limitations of Mendeleev’s periodic table.