Bromine has two naturally occurring isotopes; 79Br (mass of 78.918) and 81Br (mass of 80.916). If the atomic weight of bromine is 79.904, predict the mass spectrum of a sample of bromine atoms. (LO 2.17) (a)
(b)
(c)
(d)

Verified step by step guidance

1. Determine the relative abundance of each isotope. Let x be the fraction of 79Br and (1-x) be the fraction of 81Br.
2. Set up the equation for the average atomic mass: 78.918x + 80.916(1-x) = 79.904.
3. Solve the equation for x to find the relative abundance of 79Br.
4. Calculate the relative abundance of 81Br using 1-x.
5. Use the relative abundances to predict the mass spectrum, indicating the intensity of each isotope peak based on their relative abundances.

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, the two isotopes are 79Br and 81Br, which have masses of 78.918 and 80.916, respectively. Understanding isotopes is crucial for predicting the mass spectrum, as the relative abundance of each isotope affects the overall atomic weight.

Atomic Weight

Atomic weight is the weighted average mass of an element's isotopes, reflecting both the mass and the relative abundance of each isotope in nature. For bromine, the atomic weight of 79.904 indicates that the isotopes are not present in equal amounts, which influences the peaks observed in the mass spectrum. This concept is essential for interpreting the data from mass spectrometry.

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio of ions, showing the relative abundance of different isotopes or molecules in a sample. In the case of bromine, the mass spectrum will display peaks corresponding to the isotopes 79Br and 81Br, with their heights reflecting their relative abundances. Analyzing the mass spectrum allows for the identification and quantification of isotopes present in the sample.