Question

Explain why `""_1^3"H"` and `""_2^3"H"` are not considered isotopes.

Answer 1

Isotopes are the atoms of an element with the same atomic number but different mass numbers. There are three isotopes of hydrogen atom, namely protium `""_1^1"H"` , deuterium `""_1^2"H"`  and tritium `""_1^3"H"` . `""_1^3"H"`  and `""_2^3"H"`  are not considered as isotopes because they do not have the same atomic number. Such atoms that have same mass number but different atomic numbers are called isobars.