The atomic mass of carbon is 12.01 amu (atomic mass units).
This is not the mass of a single carbon atom, but rather the average atomic mass of all carbon isotopes found in nature. Different isotopes of carbon have different numbers of neutrons, resulting in slightly different masses. The most common isotope, Carbon-12 (¹²C), has an atomic mass of exactly 12 amu and makes up the majority of naturally occurring carbon. However, other isotopes like Carbon-13 (¹³C) also exist, contributing to the overall average atomic mass.
Understanding Atomic Mass
- Atomic Mass Units (amu): A unit of mass used to express the mass of atoms and molecules. One amu is approximately equal to the mass of a single proton or neutron.
- Isotopes: Atoms of the same element with the same number of protons but a different number of neutrons. They have the same atomic number but different atomic masses.
- Average Atomic Mass: The weighted average of the atomic masses of all naturally occurring isotopes of an element. The weighting is based on the relative abundance of each isotope.
How the Average Atomic Mass is Calculated
The average atomic mass of carbon (12.01 amu) is calculated by considering the mass and abundance of each carbon isotope. For instance, the calculation would include the contribution of the most abundant isotope, ¹²C (approximately 98.9% abundance), and less abundant isotopes such as ¹³C (approximately 1.1% abundance).
Carbon Isotopes and Their Masses
- Carbon-12 (¹²C): Atomic mass of exactly 12 amu. This isotope is used as the standard for defining the atomic mass unit.
- Carbon-13 (¹³C): Atomic mass slightly greater than 13 amu.
- Carbon-14 (¹⁴C): Radioactive isotope with an atomic mass of approximately 14 amu.
This average atomic mass is the value you will find on the periodic table.
