If the average atomic mass of Br is 79.90 amu, what is the percent abundance of each of its isotopes?

How would we figure out the isotopes first before we calculate the percent abundance??

To determine the isotopes of an element, you can refer to the periodic table. In the case of bromine (Br), the atomic number is 35, which means it has 35 protons in its nucleus. The average atomic mass of 79.90 amu is a weighted average of the different isotopes of bromine, taking into account their individual masses and abundances.

To find the isotopes of bromine, you can look at the atomic masses listed on the periodic table. Bromine has two stable isotopes: ^79Br and ^81Br. The atomic mass of ^79Br is approximately 78.92 amu, while the atomic mass of ^81Br is approximately 80.92 amu.

Now, let's calculate the percent abundance of each isotope using the average atomic mass and the atomic masses of the isotopes:

Let the percent abundance of ^79Br be x and the percent abundance of ^81Br be (100 - x) since the sum of the percentages should be 100%.

Average atomic mass = (Percent abundance of ^79Br * Atomic mass of ^79Br) + (Percent abundance of ^81Br * Atomic mass of ^81Br)

79.90 amu = (x/100 * 78.92 amu) + ((100 - x)/100 * 80.92 amu)

Now you can solve this equation to find the value of x, which will give you the percent abundance of ^79Br. Solving this equation will give you the answer.