There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of molecules, and the mass of a molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of consists of three peaks: m/zRelative Peak Intensity157.836 0.2569 159.834 0.4999 161.832 0.2431
a. What is the origin of each peak (of what isotopes does each consist)?

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Identify the isotopes of bromine: Bromine has two stable isotopes, Br-79 and Br-81.

Understand the concept of a mass spectrum: The mass spectrum shows peaks corresponding to the mass-to-charge ratio (m/z) of different isotopic combinations in a molecule.

Determine the possible combinations of isotopes in a Br2 molecule: The combinations are Br-79/Br-79, Br-79/Br-81, and Br-81/Br-81.

Calculate the m/z values for each combination: Br-79/Br-79 gives 157.836, Br-79/Br-81 gives 159.834, and Br-81/Br-81 gives 161.832.

Match each peak in the mass spectrum to the corresponding isotopic combination based on the calculated m/z values.

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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 stable isotopes are bromine-79 and bromine-81. Understanding isotopes is crucial for interpreting mass spectra, as each isotope will produce distinct peaks corresponding to their respective masses.

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio (m/z) of ions, which helps identify the composition of a sample. Each peak in the spectrum corresponds to a specific ion, with its height indicating the relative abundance of that ion. Analyzing the peaks allows chemists to determine the isotopic composition of elements in a sample, such as the different isotopes of bromine.

Relative Abundance

Relative abundance refers to the proportion of each isotope present in a sample compared to the total amount of isotopes. In the context of the mass spectrum, the intensity of each peak reflects the relative abundance of the corresponding isotopes. This concept is essential for calculating the average atomic mass of an element and understanding the distribution of isotopes in a sample.

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The element lead (Pb) consists of four naturally occurring isotopes with atomic masses 203.97302, 205.97444, 206.97587, and 207.97663 amu. The relative abundances of these four isotopes are 1.4, 24.1, 22.1, and 52.4%, respectively. From these data, calculate the atomic weight of lead.

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Gallium (Ga) consists of two naturally occurring isotopes with masses of 68.926 and 70.925 amu. 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 Ga is 69.72 amu. Calculate the abundance of each isotope.

Textbook Question

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of molecules, and the mass of a molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of consists of three peaks: m/zRelative Peak Intensity157.836 0.2569 159.834 0.4999 161.832 0.2431

b. What is the mass of each isotope?

Textbook Question

c. Determine the average molecular mass of a molecule.

Textbook Question

d. Determine the average atomic mass of a bromine atom.