Question

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What is the average atomic mass of the element?

An element, X, has two isotopes, X-14 and X-15. Use the data in the table to find the average atomic mass of element X.

Isotope Atomic Mass Abundance (%)
X-14 14.003 99.636
X-15 15.000 0.364


The average atomic mass of element X is
amu.

Answer 1

Answer: Average atomic mass of an element is the summation of the masses of its isotopes, each multiplied by its natural abundance.

Average atomic mass = A₁M₁ + A₂M₂ +… + AnMn

Average atomic mass of element X is 13.9790 amu.

Step-by-step explanation:

Average atomic mass = A₁M₁ + A₂M₂ +… + AnMn)

where, A is % abundance and M is atomic mass of element

To find : average atomic mass of element X

Let's take abundance of each isotopes as;

Abundance of X-14 = 99.636% = 0.99636

Abundance of X-15 = 0.364% = 0.00364

As per given data, atomic mass of the element X-14 is 14.003 and

X-15 15.000 amu.

As per given formula: we get,

Avg. atomic mass = (14.003)*(0.99636) + (15.000)*(0.00364)

Calculating this expression gives us:

So, Avg. atomic mass = 13.92445 + 0.0546 = 13.97905 amu