why is the relative atomic mass of element not a whole number?
The Correct Answer and Explanation is:
The relative atomic mass of an element is generally not a whole number because it reflects the weighted average mass of all the naturally occurring isotopes of that element. Elements often exist as mixtures of isotopes, which are atoms of the same element that have the same number of protons but different numbers of neutrons, leading to different atomic masses.
For example, carbon exists primarily as two isotopes: carbon-12 (with an atomic mass of 12 atomic mass units, amu) and carbon-14 (with an atomic mass of approximately 14 amu). However, these two isotopes are not present in equal amounts. The majority of naturally occurring carbon is carbon-12, but a small proportion is carbon-14. The relative atomic mass of carbon is calculated by taking the weighted average of the atomic masses of these isotopes, taking into account their relative abundances. This results in a value that is close to 12 but not exactly 12 because the presence of carbon-14, which has a higher atomic mass, influences the average.
To further explain, consider the element chlorine. Chlorine exists in nature as two isotopes: chlorine-35 (with an atomic mass of 35 amu) and chlorine-37 (with an atomic mass of 37 amu). The relative abundance of chlorine-35 is about 75%, while chlorine-37 makes up the remaining 25%. When calculating the relative atomic mass of chlorine, we weigh these isotopes according to their natural abundances. As a result, the relative atomic mass of chlorine is around 35.5, which is not a whole number.
In summary, the relative atomic mass is a weighted average of the atomic masses of an element’s isotopes, and since the isotopes have different masses and relative abundances, the overall atomic mass is rarely a whole number.
