On most periodic tables a single atomic mass is listed instead of the mass numbers for all the stable isotopes. How is this mass related to the different isotopes?

Since atoms of the same element can vary in number of neutrons, isotopes of elements exist. Since neutrons have mass more or less of them in an atom affects its mass. Mass number is the average mass of the isotopes of an element with respect to the relative abundance of each isotope.

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Аноним Аноним · Answer 2 · 2019-12-30T07:35:44+01:00

Answer: The mass of the atom is basically the average atomic mass of all the stable isotopes.

Explanation:

Average atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

[tex]\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i[/tex]

For Example: Taking the element silicon

Three isotopes of Silicon, which are Si-28, Si-29 and Si-30.

Average atomic mass of silicon = 28.086 amu

As, the average atomic mass of silicon is closer to the mass of Si-28 isotope. This means that the relative abundance of this isotope is the highest as compared to the other two isotopes.

Percentage abundance of Si-28 isotope = 92.2%

Percentage abundance of Si-29 isotope = 4.7 %

Percentage abundance of Si-30 isotope = 3.1%

Hence, the mass of the atom is basically the average atomic mass of all the stable isotopes.