How to Find the Mass Number of a Boron Isotope
- 1). Determine how many neutrons the isotope of boron contains. If you are working on a test problem, it should provide this information. In this example, assume that the isotope of boron has eight neutrons.
- 2). Add the number of neutrons to the number of protons in a boron atom, which is five. In this example, the result is 13. This is the mass number of the boron isotope. Each atom of this isotope weighs approximately 13 atomic mass units, and a mole of atoms (6.02 x 10^23 atoms) weighs 13 grams.
- 3). Check to see if the isotope is labeled as "boron" followed by a number (e.g., "boron-8" or "boron-12"). In this case, the number after the name is the sum of the protons and neutrons, and is therefore the same as the mass number. Note that you can calculate the number of neutrons in the atom by subtracting the number of protons from the mass number.
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