Question

Bromine has two naturally occurring isotopes, bromine-79 atomic mass = 78.9183 u; abundance = 50.69%2 and bromine-81 atomic mass = 80.9163 u; abundance = 49.31%2. Calculate the atomic weight of bromine.

Answer 1

The atomic weight of bromine can be calculated by multiplying the exact mass of each isotope (bromine-79 and bromine-81) by its corresponding abundance in decimal form, and then summing these values to get the average atomic mass of 79.90 amu.

Step-by-step explanation:

The student is asking to calculate the atomic weight of bromine, which has two naturally occurring isotopes: bromine-79 and bromine-81. To calculate this, we take the exact mass of each isotope and multiply it by its abundance in percentage form. The abundance percentages must first be converted to decimal form by dividing them by 100.

For bromine-79 (⁹⁹Br), the calculation will be as follows:
78.9183 amu (atomic mass unit) × 0.5069 (50.69%/100) = 40.00 amu

For bromine-81 (₈₁Br), the calculation will be:
80.9163 amu × 0.4931 (49.31%/100) = 39.90 amu

The final step is to add these results together to find the atomic mass of bromine:
40.00 amu + 39.90 amu = 79.90 amu, which is the average atomic mass of bromine.