# Number of protons, electrons, & neutrons from mass number & atomic number

In this post, we will see how to calculate the number of protons, electrons, & neutrons from the mass number & the atomic number of an element.

**how to calculate the number of protons, electrons, & neutrons from the mass number & the atomic number of an element?**

We have to remember and use the following 2 formulas:

**Atomic number = number of protons = number of electronsMass number = number of neutrons + number of protons**

We will take one example to understand the procedure. Say, we need to find out the number of protons, electrons, and neutrons in an atom of chlorine-37.

We will use the above-mentioned formulas to do this calculation.

The mass number of chlorine-37 is 37. Consulting the periodic table reveals that chlorine’s atomic number is 17.

Therefore we know that:

atomic number = number of protons = number of electrons = 17 protons and 17 electrons

number of neutrons = mass number – atomic number = 37 – 17 = 20 neutrons

Hence, we can summarize that an atom of chlorine-37 is made up of 17 electrons, 17 protons, and 20 neutrons.

## Assignment

- How many protons, electrons, and neutrons make up an atom of bromine-80?
- Write the nuclear symbol for carbon-13.
- Write the hyphen notation for the isotope with 15 electrons and 15 neutrons.