state the position of

(i) isotopes of the same element

(ii) hydrogen in the modern periodic table

Dear Student, 

(1) Modern periodic table is arranged in order of increasing atomic numbers.

Isotopes are those which have same atomic number but different mass number.

Hence isotopes will be placed at the same place as their atomic numbers are same.

(2) Hydrogen is considered as a very unique element. The position of this small element in the periodic table is debatable.

Hydrogen’s position was not justified in the very old Mendeleev’s periodic table. He positioned hydrogen in the first column above alkali metals. He did so because hydrogen and alkali metals have similar properties. For example, hydrogen reacts with halogens, oxygen, and sulphur to form compounds whose formulae are similar to those of alkali metals.

Hydrogen also resembles halogens in many ways. Like halogens, hydrogen is a gas, and exists as a diatomic molecule (H2). It forms covalent compounds like halogens unlike alkali metals. Hence, it can also be placed above the halogen group.

THESE PROPERTIES LEAD TO THE UNEXPLAINED POSITION OF HYDROGEN