Question

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

Answer 1

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 `""^1H, ""^2H, "and " ""^3H`, respectively.

For your problem we would write `""^35Cl, "and " ""^37Cl`; for both isotopes the elemental symbol specifies `Z=17`.

Capisce?