Question

How to calculate atomic weight?
Explain with examples...​

Answer 1

Answer:

Calculating Average Atomic Mass

Average atomic mass = f1M1 + f2M2 +… + fnMn where f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope. The average atomic mass of an element can be found on the periodic table, typically under the elemental symbol.

Answer 2

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The atomic weight is calculated by adding the mass of each isotope multiplied by its fractional abundance. For example, for an element with 2 isotopes:

atomic weight = massa x fractb + massb x fractb

If there were three isotopes, you would add a 'c' entry. If there were four isotopes, you'd add a 'd', etc.

Atomic Weight Calculation Example:-

If chlorine has two naturally-occurring isotopes where:

Cl-35 mass is 34.968852 and fract is 0.7577

Cl-37 mass is 36.965303 and fract is 0.2423

atomic weight = massa x fracta + massb x fracb

atomic weight = 34.968852 x 0.7577 + 36.965303 x 0.2423

atomic weight = 26.496 amu + 8.9566 amu

atomic weight = 35.45 amu

Tips for Calculating Atomic

• The sum of the fractional abundance values must equal 1.

• Be sure to use the mass or weight of each isotope and not its mass number.