Isotopes are variations of chemical elements that have the same number of protons but different numbers of neutrons. We identify isotopes based on their mass, which is the sum of protons and neutrons. Carbon has three main isotopes: 12C with 6 protons and 6 neutrons; 13C with 6 protons and 7 neutrons; and 14C with 6 protons and 8 neutrons. Isotopes are identified by their distinct masses, which are measured using an isotope ratio mass spectrometer.

1. What are isotopes?
1cm Isotopes are variations of
chemical elements that
have the same number of
protons but different
numbers of neutrons.

2. What are isotopes?
1cm Isotopes are variations of
chemical elements that
have the same number of
protons but different
numbers of neutrons.
We identify isotopes based
on their mass, whereby the
sum of protons and
neutrons equals the mass of
the isotope.

3. What are isotopes?
1cm This carbon atom has a
mass of 12:
6 protons + 6 neutrons.

4. What are isotopes?
1cm This carbon atom has a
mass of 12:
12
C
6 protons + 6 neutrons.
The name of this isotope,
then, is 12C:
C for carbon, 12 for its mass.

5. What are isotopes?
1cm Two other isotopes of carbon
exist in addition to 12C. They
are:
12
C 6 protons
+ 6 neutrons

6. What are isotopes?
1cm Two other isotopes of carbon
exist in addition to 12C. They
are:
12
C 6 protons 13
C 6 protons
+ 6 neutrons + 7 neutrons
and…

7. What are isotopes?
1cm Two other isotopes of carbon
exist in addition to 12C. They
are:
12
C 6 protons 13
C 6 protons
+ 6 neutrons + 7 neutrons
14
C 6 protons
+ 8 neutrons

8. What are isotopes?
C
12 1cm 6 protons 13
C 6 protons
+ 6 neutrons + 7 neutrons
14
C 6 protons
Since isotopes have distinct + 8 neutrons
masses, we identify C isotopes in
our samples by measuring the mass
of the carbon atoms. We use an
instrument called an isotope ratio
mass spectrometer to make these
measurements.