What is the average atomic mass of bromine (Br) as listed on the periodic table?

• A. 79.90 u
• B. 126.90 u
• C. 35.45 u
• D. 47.88 u

Answer: (A)

Verified step by step guidance

1. Understand that the average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes, based on their relative abundances.
2. Identify the naturally occurring isotopes of bromine and their respective atomic masses and percent abundances. For bromine, the two main isotopes are typically \(^{79}\text{Br}\) and \(^{81}\text{Br}\).
3. Use the formula for average atomic mass: \[ \text{Average Atomic Mass} = (\text{fractional abundance of isotope 1} \times \text{mass of isotope 1}) + (\text{fractional abundance of isotope 2} \times \text{mass of isotope 2}) + \ldots \]
4. Convert the percent abundances of each isotope into decimal form (fractional abundances) by dividing by 100.
5. Multiply each isotope's mass by its fractional abundance and sum these values to find the average atomic mass, which corresponds to the value listed on the periodic table.