L'indium (Z=49) possède cinq isotopes: ^111 ln, ^112 ln,...

L'indium $(\mathrm{Z}=49)$ possède cinq isotopes: ${ }^{111} \ln ,{ }^{112} \ln ,{ }^{113} \ln ,{ }^{114} \ln$, et ${ }^{115} \ln$, mais il est formé en presque totalité de deux de ces isotopes seulement et sa masse atomique apparente est 114,82 . L'un des deux isotopes étant ${ }^{113} \ln$, quel est l'autre ?

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Key Concepts

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different mass numbers. This concept is fundamental when dealing with elements that exist naturally in multiple forms, as their individual masses influence the overall properties of the element.

Atomic Mass

Atomic mass is the weighted average mass of the atoms of an element, accounting for the different masses of its isotopes and their relative abundances. This value reflects the composite contribution of each isotope in natural samples, rather than simply being an arithmetic mean of the mass numbers.

Isotopic Abundance

Isotopic abundance refers to the relative proportions of different isotopes of an element that occur naturally. These proportions are essential for calculating the average atomic mass since each isotope contributes to the overall mass based on how common it is.

Weighted Average Calculation

Weighted average calculation is the method used to determine the atomic mass of an element by multiplying the mass of each isotope by its relative abundance and summing these products. This approach explains why the average atomic mass might be closer to the mass of the more abundant isotope, which is crucial in understanding the overall atomic mass of elements with multiple isotopes.

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