How are isotopes written using chemical symbols, atomic numbers, and mass numbers?

To represent an isotope, you use the chemical symbol of the element combined with its atomic number and mass number.

The standard notation is written as:
$${}_Z^A\text{Sy}$$

In this format:
* Sy is the one- or two-letter chemical symbol of the element.1
* Z is the atomic number, representing the number of protons in the nucleus.1
* A is the mass number, which is the sum of the protons and neutrons in the nucleus.12

For example, the isotope of uranium used in nuclear power is written as ${}_{92}^{235}\text{U}$.1

Alternatively, if you prefer not to use the full symbolic notation, you can identify an isotope by writing the element's name followed by its mass number, such as uranium-235 or carbon-14.13