# Carbon has an atomic number of 6. How many protons and neutrons are in a nucleus of carbon-13?

Jan 20, 2017

The isotope $\text{_6^13"C}$ has 6 protons and 7 neutrons.

#### Explanation:

To be carbon the atom must have 6 protons.

Each proton has a mass of 1 u for a total of 6 u.

The nucleus of $\text{_6^13"C}$ has a mass of 13 u.

Subtracting the 6 u from the mass of the protons leaves 7 u:

$\text{13 u - 6 u = 7 u}$

Each neutron has a mass of 1 u. The 7 u left are accounted for by 7 neutrons.