Question

What is the atomic mass of bromine?

Short answer

The atomic mass of bromine is approximately 79.872 amu.

Step-by-step solution

Understanding Atomic Mass

Atomic mass, also known as atomic weight, is the average mass of atoms of an element, measured in atomic mass units (amu). It considers the different isotopes and their abundances.

Identifying Bromine Isotopes

Bromine has two major naturally occurring isotopes: Bromine-79 and Bromine-81. These isotopes have masses of 78.918 amu and 80.916 amu, respectively.

Determining Isotopic Abundances

The approximate natural abundance of Bromine-79 is 50.7%, and for Bromine-81, it is 49.3%. These percentages are derived from analyses of natural bromine samples.

Calculating Average Atomic Mass

Using the formula for average atomic mass: \[ \text{Atomic mass} = (\text{mass of isotope 1} \times \text{abundance of isotope 1}) + (\text{mass of isotope 2} \times \text{abundance of isotope 2}) \]Substitute with bromine's values:\[ \text{Atomic mass} = (78.918 \times 0.507) + (80.916 \times 0.493) \]

Solving the Equation

Multiply each isotopic mass by its abundance:\[ 78.918 \times 0.507 = 39.997 \]\[ 80.916 \times 0.493 = 39.875 \]Add these results together to find the average atomic mass:\[ 39.997 + 39.875 = 79.872 \] amu.

Key concepts

Isotopic Abundance

Isotopic abundance is a crucial concept in understanding the composition of elements such as bromine. Elements often exist in nature as mixtures of isotopes. Each isotope of an element has a distinct number of neutrons, leading to variations in mass. The isotopic abundance tells us the relative amount of each isotope present in a sample of the element.
For bromine, there are two naturally occurring isotopes: Bromine-79 and Bromine-81. The abundance of these isotopes is expressed in percentages. For Bromine-79, the abundance is about 50.7%, while Bromine-81 has an abundance of approximately 49.3%. This means that in a sample of bromine, about half of the atoms are Bromine-79, and the other half are Bromine-81.

• Isotopic abundances are often measured in percentages.
• They provide the proportion of each isotope in a natural sample.
• Understanding isotopic abundance is vital for calculating the atomic mass of an element.

By knowing the isotopic abundance, scientists can calculate a more accurate atomic mass for an element.

Atomic Mass Units

Atomic mass is typically measured in atomic mass units (amu), a standard unit of mass that quantifies the mass on an atomic or molecular scale. One atomic mass unit is defined as one twelfth of the mass of a carbon-12 atom, approximately equivalent to 1.66 x 10^{-27} kilograms.

This unit allows chemists and physicists to express the mass of one mole of an atom or molecule in a way that is easier to handle than using kilograms, because the numbers are relatively larger and more manageable.
For example, the atomic mass of Bromine-79 is 78.918 amu, while Bromine-81 is 80.916 amu. These are precise measurements that reflect the average mass of an atom as it exists in nature.

• Atomic mass units allow for a consistent method of comparing masses at an atomic level.
• This measurement is crucial in the field of chemistry and physics.

In calculations, using amu simplifies the values, making it easier to understand the relative weights among different atoms.

Bromine Isotopes

Bromine is an element that consists mainly of two isotopes: Bromine-79 and Bromine-81. These isotopes differ due to their distinct numbers of neutrons, although they both have the same number of protons, defining them as bromine.

These isotopes are common in nature, making up the bulk of naturally occurring bromine. The mass of Bromine-79 is 78.918 amu, while Bromine-81 has a mass of 80.916 amu.
The difference in mass between the isotopes is due to the difference in neutron numbers, which affects their atomic mass. Yet, chemically, these isotopes behave similarly because they have the same electron configuration.

• Bromine isotopes are used in various scientific applications.
• The analysis of isotopic ratios is important in chemical, environmental, and geological studies.

Understanding the unique characteristics of these isotopes is essential for proper application in scientific analysis and industry.

Average Atomic Mass Calculation

The average atomic mass of an element like bromine is a weighted average of its isotopes' masses based on their natural abundance. This provides a realistic measurement of the element's mass as encountered in the real world.

For bromine, calculating the average atomic mass involves considering both Bromine-79 and Bromine-81. The calculation formula is:

\[ \text{Atomic mass} = (\text{mass of isotope 1} \times \text{abundance of isotope 1}) + (\text{mass of isotope 2} \times \text{abundance of isotope 2}) \]

Applying bromine's values, we use:

• Mass of Bromine-79: 78.918 amu
• Abundance of Bromine-79: 50.7% \( \Rightarrow 0.507 \)
• Mass of Bromine-81: 80.916 amu
• Abundance of Bromine-81: 49.3% \( \Rightarrow 0.493 \)

Calculate step by step:

1. Multiply the mass of each isotope by its respective abundance.
2. \( 78.918 \times 0.507 = 39.997 \)
3. \( 80.916 \times 0.493 = 39.875 \)
4. Add the results to get the average atomic mass:
\[ 39.997 + 39.875 = 79.872 \text{ amu} \]
This calculation reveals the true atomic mass of bromine, as it averages the mass based on how we find bromine in nature.