Question

The two elements with same number of electrons but different mass numbers are known as ______.

Answer 1

Isotopes:

1. Isotopes are two elements that have the same number of electrons but differing masses.
2. Isotopes differ in relative atomic mass but not in chemical characteristics because they have different numbers of neutrons but equal quantities of protons in their nuclei.
3. Example: ${}_{17}{}^{}\mathrm{Cl}^{35}\mathrm{and}{}_{17}{}^{}\mathrm{Cl}^{37}$.