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 (b) What is the mass of each isotope?

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Identify the isotopes of bromine involved. Bromine has two stable isotopes, Br-79 and Br-81, which are the most likely candidates for the peaks observed in the mass spectrum.

Understand that the mass spectrum peaks represent the combinations of these isotopes in a Br₂ molecule. The possible combinations are Br-79/Br-79, Br-79/Br-81, and Br-81/Br-81.

Calculate the theoretical mass of each Br₂ molecule combination: Br-79/Br-79 would have a mass of 79 u + 79 u, Br-79/Br-81 would have a mass of 79 u + 81 u, and Br-81/Br-81 would have a mass of 81 u + 81 u.

Match these calculated masses to the peaks observed in the mass spectrum to determine which peak corresponds to which molecule combination.

From the peak assignments, deduce the mass of each bromine isotope: Br-79 and Br-81.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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 typically bromine-79 and bromine-81. Understanding isotopes is crucial for analyzing mass spectra, as the relative abundance of each isotope affects the overall mass of the molecule.

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio of ions, which helps identify the composition of a sample. In the case of bromine, the mass spectrum shows peaks corresponding to the different isotopes of Br<sub>2</sub>, with each peak's height indicating the relative abundance of each isotope. Analyzing these peaks allows for the determination of the isotopic masses.

Molecular Mass Calculation

The molecular mass of a compound is calculated by summing the atomic masses of its constituent atoms. For Br<sub>2</sub>, the molecular mass is the combined mass of two bromine atoms, which can be derived from the isotopic masses and their relative abundances shown in the mass spectrum. This calculation is essential for determining the individual masses of the isotopes present.

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Textbook Question

Copper (Cu) consists of two naturally occurring isotopes with masses of 62.9296 and 64.9278 u. (a) How many protons and neutrons are in the nucleus of each isotope? Write the complete atomic symbol for each, showing the atomic number and mass number. (b) The average atomic mass of Cu is 63.55 u. Calculate the abundance of each isotope.

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Textbook Question

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 (a) What is the origin of each peak (of what isotopes does each consist)?

Textbook Question

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 Br₂molecule.

Textbook Question

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 (d) Determine the average atomic mass of a bromine atom

Textbook Question

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 (e) Calculate the abundances of the two isotopes. Calculate the abundance of the heavier isotope.