Illustrated Glossary of Organic Chemistry

Carbon-12 (12C): The carbon isotope whose nucleus contains six protons and six neutrons. This gives an atomic mass of 12 amu.



The nucleus of carbon-12 contains six protons and
six neutrons, resulting in an atomic mass of 12 amu.
  
The nucleus of carbon-13 contains six protons and
seven neutrons, resulting in an atomic mass of 13 amu.
  
The nucleus of carbon-14 contains six protons and
eight neutrons, resulting in an atomic mass of 14 amu.