The relative atomic mass of carbon is approximately 12.01 atomic mass units (amu). The atomic mass of an element is determined by the weighted average of the masses of its naturally occurring isotopes. Carbon has two stable isotopes: carbon-12 and carbon-13.
Carbon-12 is the most abundant isotope, making up about 98.93% of naturally occurring carbon atoms. It has a mass of exactly 12 atomic mass units.
Carbon-13 is the less abundant isotope, constituting about 1.07% of the atoms. It has a mass of approximately 13.003355 amu.
To calculate the relative atomic mass of carbon, the masses of the isotopes are multiplied by their respective abundances and then added together:
Relative atomic mass of carbon = (isotope 1 mass × isotope 1 abundance) + (isotope 2 mass × isotope 2 abundance)
= (12 amu × 0.9893) + (13.003355 amu × 0.0107)
= 11.8716 amu + 0.1398 amu
= 12.0114 amu
Rounded to two decimal places, the relative atomic mass of carbon is approximately 12.01 amu.