How does isotopic abundance affect relative atomic mass?

Isotopic abundance affects relative atomic mass by contributing to the average mass of an atom of an element.

In more detail, isotopes are different forms of the same element that have the same number of protons but different numbers of neutrons. This means that they have different atomic masses. For example, carbon-12 and carbon-14 are isotopes of carbon, with carbon-12 having 6 neutrons and carbon-14 having 8 neutrons.

Isotopic abundance refers to the percentage of each isotope of an element that exists in nature. For instance, about 99% of carbon on Earth is carbon-12, while only about 1% is carbon-14. This means that the isotopic abundance of carbon-12 is much higher than that of carbon-14.

The relative atomic mass of an element is the weighted average of the atomic masses of its isotopes, taking into account their isotopic abundances. In other words, it's not just a simple average, but one where each isotope's mass is multiplied by its abundance before all the values are added together.

So, if an element has one isotope that is much more abundant than the others, this isotope will have a greater effect on the relative atomic mass of the element. In the case of carbon, the relative atomic mass is close to 12, because carbon-12 is so much more abundant than carbon-14.

Therefore, the isotopic abundance of each isotope of an element plays a crucial role in determining the element's relative atomic mass. It's the reason why the relative atomic mass of most elements is not a whole number, but a decimal.