# What are some common mistakes students make with isotope notation?

##### 1 Answer
Mar 5, 2017

Writing mass and atomic numbers the wrong way round.

#### Explanation:

Isotopes are written as ""_Z^A X, where X is the element, Z is the atomic number and A is the atomic mass.

I was guilty of this for a long time too, I'd write the mass on the bottom because it's larger so it made more sense.

Isotopes should always be written with the big number on top.