Question

Write a short note on Position of isotopes in the Mendeleev’s and the modern periodic table.

Answer 1

We have to know that isotopes are the atoms having the same atomic number but different mass number. Mendeleev’s periodic table does not explain the electronic arrangement of elements. Elements which are chemically similar such as Gold and Platinum have been placed in separate groups.

Complete answer:
As we know, isotopes are the atoms of the same element having different atomic masses. Therefore, according to Mendeleev’s classification these should be placed at different places depending upon their atomic masses. For example: hydrogen isotopes with atomic masses $1$, $2$ and $3$ should be placed at three places. However, isotopes have not been given separate places in the periodic table because of their similar properties. Isotopes have similar chemical properties but different masses. Based on periodic law an isotope is an element which must have a separate place in the periodic table. However there are no places for isotopes in the Mendeleev periodic table. Since isotopes have the same atomic number they haven't been given any specific position in the modern periodic table. According to Mendeleev's Periodic Law, isotopes of an element must be given separate places in the periodic table because they have different atomic masses. Isotopes could not find a position in Mendeleev's periodic table because those were arranged according to atomic number in the increasing order but isotopes have the same atomic number.

Note:
We need to know that all the isotopes of an element have the same number of protons, so their atomic number is also the same. Since, all the isotopes of an element have the same atomic number; they can be put at one place in the same group of the periodic table.