# Chlorine has two principle isotopes, Cl-35 and Cl-37. How do you write out these isotopes in correct isotope notation?

Aug 30, 2016

The mass number of an isotope is usually supercripted to the upper left of the elemental symbol.

#### Explanation:

Sometimes, the atomic number, $Z$ is subscripted to the lower left, however, the elemental symbol unequivocally identifies the element's identity, and thus identifies $Z$.

For common hydrogen isotopes, protium, deuterium, and tritium, we would write ${\text{^1H, ""^2H, "and " }}^{3} H$, respectively.

For your problem we would write ${\text{^35Cl, "and " }}^{37} C l$; for both isotopes the elemental symbol specifies $Z = 17$.

Capisce?