Final answer:
Fractional atomic weight is the weighted average atomic mass of an element, considering isotope abundances. Some elements have atomic masses that are not whole numbers due to the mixture of isotopes.
Explanation:
Fractional atomic weight refers to the atomic mass of an element, which is a weighted average of the masses of the isotopes that compose the element. This average takes into account the abundance of each isotope to calculate the overall atomic mass. An example is boron, which has isotopes 10B and 11B with different masses and abundances contributing to its atomic mass calculation.
Atomic masses of some elements are not whole numbers because they are calculated as weighted averages considering the proportions of different isotopes. Since isotopes have different masses and occur in varying percentages in nature, the atomic mass is a reflection of this mixture, resulting in fractional values.
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