# If an isotope of carbon has a atomic mass of 13, then how many protons does it have?

Oct 16, 2016

If it is a carbon isotope, then it MUST have 6 protons, i.e. 6 positively charged $\text{nucular}$ particles.

#### Explanation:

The identity of an atom is characterized by its atomic number, $Z$.

$Z = 1$, the element is hydrogen; $Z = 2$, the element is helium;...... $Z = 26$, the element is iron.

And if $Z = 6$, the element is carbon. Of course, a given nucleus may contain various, differing numbers of neutrons, and this gives rise to the phenomenon of isotopes, the same element with a different mass. Most carbon nuclei contain 6 neutrons, i.e. 6 massive nuclear particles with zero charge, and thus the most numerous istope is ""^12C, a few contain 7 neutrons to give ""^13C, which is a very important isotope for direct characterization of organic molecules, and an even smaller percentage of carbon nuclei contain 8 neutrons to give the ""^14C isotope.

In short, the number of protons determine $Z$, and thus the identity of the element; the number of neutrons determine the mass. Most heavier elements have a range of isotopes, and the average isotopic mass is quoted on the Periodic Table.