There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br₂ molecules, and the mass of a Br2 molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br₂ consists of three peaks: Mass (u) Relative Size 157.836 0.2569 159.834 0.4999 161.832 0.2431 (c) Determine the average molecular mass of a Br₂ molecule.

Verified step by step guidance

1. Identify the masses and their relative abundances from the mass spectrum data provided. The masses are 157.836 u, 159.834 u, and 161.832 u with relative abundances of 0.2569, 0.4999, and 0.2431 respectively.
2. Calculate the contribution of each mass to the average molecular mass by multiplying each mass by its corresponding relative abundance.
3. Sum up all the contributions from step 2 to get the total average molecular mass of the Br₂ molecule.
4. Ensure the units are consistent throughout the calculations, using atomic mass units (u) for all masses.
5. Interpret the result as the average mass of a Br₂ molecule based on the given mass spectrum data.

Key Concepts

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For bromine, there are two stable isotopes: Br-79 and Br-81. The presence of these isotopes affects the average atomic mass of bromine and consequently the molecular mass of Br2, as the molecular mass is calculated based on the isotopic composition.

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio of ions, which helps identify the different isotopes and their relative abundances in a sample. In the case of Br2, the mass spectrum shows three peaks corresponding to the different isotopic combinations of bromine atoms, allowing for the determination of the average molecular mass based on the relative sizes of these peaks.

Average Molecular Mass

The average molecular mass of a compound is calculated by taking the weighted average of the masses of its constituent atoms, considering their relative abundances. For Br2, this involves multiplying the mass of each isotopic form by its relative abundance and summing these products to find the overall average mass of the molecule. This concept is crucial for understanding how isotopic variations influence the properties of compounds.