Question

There are 3 isotopes of carbon. $Carbon - 12$ , $Carbon - 13$ and $Carbon - 14$ . The average atomic mass of carbon is $12.011$ . Which isotope of carbon is the most abundant? Why?

Answer 1

The average atomic mass of any element that contains more than one isotope is calculated by taking into consideration the relative percentage of abundance of each isotope. The most abundant isotope is likely to have the highest impact on average atomic mass.

Complete answer:
Carbon is the first member of the fourteenth group of the modern periodic table and contains four electrons in its outermost shell due to which it is called tetravalent.
Carbon is known to exist in more than one elemental form in nature, the different types of carbon element have the same number of protons in their nuclei (as well as same number of electrons in neutral states) but different number of neutrons. Thus, these elemental forms have the same chemical symbol and atomic numbers but different mass numbers and are called isotopes.
The three isotopes of carbon are $Carbon - 12$ , $Carbon - 13$ and $Carbon - 14$ . These isotopes are not found in equal amounts in nature. Nature has a rich source of some of these isotopes while the other ones are less stable and only found in minute amounts.
The relative abundance when multiplied by the atomic mass number of each isotope gives the average atomic mass. Thus, the average atomic mass value is closest to the mass of isotopes that has highest relative abundance in nature.
$\Rightarrow$ The average atomic mass value for carbon isotopes is $12.011$ which is closest to the $Carbon - 12$ isotope and therefore $Carbon - 12$ is the most abundant isotope.

Note:
A greater number of neutrons in the nucleus as compared to protons makes the atom very unstable due to which heavier nuclei are always less abundant and tend to disintegrate. As a result, the isotopes with lower atomic mass are usually more abundant and popularly used to represent the chemical species.