The of the
C atom is *defined* to be *exactly*
12 amu. This means there are an infinite number of significant figures
in the mass of carbon-12. The mass of C is 12.011 amu. What? Is it
12.(infinite 0's) amu or is it 12.011 amu?

- The atomic mass scale is
*defined*by the mass of the C atom. Note that this is a*specific*isotope of carbon. All other atomic masses are relative to the mass of this atom. In addition, the mole is a number unit defined from the atomic mass scale as the number of particles in*exactly*12 g of carbon-12. The molar mass of carbon-12 is defined to be exactly 12 g/mol. - What does the symbol C represent? Recall that there are three 'common'
isotopes of carbon:
C,
C and
C.
The symbol C represent 'natural carbon,' which means a sample of carbon
that contains all three isotopes distributed in their natural relative
abundances.
- The molar mass of natural carbon is the mass of one mole of natural
carbon. Taken relative to one mole of carbon-12, the molar mass of
natural carbon is experimentally found to be 12.011 g/mol. Further,
this mass is the
*average*mass as calculated from

Using 98.9% for the natural abundance (probability) of carbon-12 and 1.1% for the probability of carbon-13, the average carbon mass is calculated to be 12.011 amu. - This applies to other elements as well.

- The molar mass of natural carbon is the mass of one mole of natural
carbon. Taken relative to one mole of carbon-12, the molar mass of
natural carbon is experimentally found to be 12.011 g/mol. Further,
this mass is the