How do I Calculate a Neutron's Given Mass?

Single-element atoms contain protons, electrons and neutrons. Electrons have virtually no weight and are negligible in the calculation of atomic weight. You can calculate the mass of the neutrons in an element by subtracting the weight of the protons (atomic number) from the weight of the neutrons and protons combined (atomic mass). This requires simple math skills and a periodic table with given atomic mass and atomic numbers.

Things You'll Need

• Periodic table

Instructions

1. Locate the element that you are dealing with on the periodic table. Note that if the element is a gas, you can find it on the right side of the periodic table; if the element is a metal you can find it on the left side of the periodic table.

2. Locate the value of the atomic number and atomic mass (mass number) of the element. Note that atomic number is always an integer, while the atomic mass is sometimes a decimal. This is because the recorded atomic mass is a calculated average atomic mass for that specific element.

3. Round the atomic mass to the nearest whole integer, unless you know the specific isotope for the element you are dealing with. For example, if you are dealing with hydrogen, the atomic mass is 1.00794. Round that number to 1, unless you know that you are dealing with a hydrogen isotope (an example is 2H). In that case, the atomic mass is 2.

4. Subtract the atomic number from the rounded (or isotope) atomic mass to learn the mass of the neutrons. Note that this also tells you the number of neutrons in the atom. For example if you are calculating the neutron mass of a standard atom of oxygen, you subtract 8 from 15.9994 or 16. This tells you that oxygen has eight neutrons and each neutron weighs one atomic mass unit (amu). Therefore the mass of the neutrons is 8 amu.

References

• John Jay College of Criminal Justice: Atomic Structure
• ThinkQuest: Atomic Nomenclature
• School for Champions: Atomic Weight
• Periodic Table: The Photographic Periodic Table of Elements