Question

Name or state the following:

Atoms of the same element differing in mass numbers.

Answer 1

Atoms of the same element differing in mass numbers are called as isotopes.

Example: ${}_{17}{}^{35}\mathrm{Cl}$ and ${}_{17}{}^{37}\mathrm{Cl}$. These two isotopes are of the same element i.e.; Chlorine (Cl). Mass number of ${}_{17}{}^{35}\mathrm{Cl}$ is 35 and ${}_{17}{}^{37}\mathrm{Cl}$ is 37.

• The different mass numbers exist due to the difference in number of neutrons as both the isotopes have same number of protons i.e.; 17.
• Mass number = Number of protons+ Number of neutrons