How to Find the Number of Neutrons in an Atom
Locate the element on the periodic table., Find the element’s atomic number., Find the element’s atomic weight., Round off the atomic weight to the nearest whole number to find the atomic mass., Subtract the atomic number from the atomic mass...
Step-by-Step Guide
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Step 1: Locate the element on the periodic table.
For this example, we’ll look at osmium (Os), which is in the sixth row down. -
Step 2: Find the element’s atomic number.
This tends to be the most visible number pertaining to a given element and usually sits above the element symbol. (On the chart we're using, in fact, no other numbers are listed.) The atomic number is the number of protons in a single atom of that element.
Os is number 76, meaning one atom of osmium has 76 protons. , This number is usually found beneath the atomic symbol.
Note that the chart in this example is based solely on atomic number and doesn’t list the atomic weight.
This won’t always usually be the case.
Osmium has an atomic weight of
190.23. , In our example,
190.23 would be rounded to 190, resulting in an atomic mass of 190 for osmium. , Since the vast majority of an atom’s mass is found its protons and neutrons, subtracting the number of protons (i.e. the atomic number) from the atomic mass will give you the calculated number of neutrons in the atom.
The numbers after the decimal point represent the usually very small mass of the electrons in the atom.
In our example, this is: 190 (atomic weight) – 76 (number of protons) = 114 (number of neutrons). , To find the number of neutrons in the future, simply use this formula:
N = M – n N = number of Neutrons M = atomic Mass n = atomic number -
Step 3: Find the element’s atomic weight.
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Step 4: Round off the atomic weight to the nearest whole number to find the atomic mass.
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Step 5: Subtract the atomic number from the atomic mass.
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Step 6: Remember the formula.
Detailed Guide
For this example, we’ll look at osmium (Os), which is in the sixth row down.
This tends to be the most visible number pertaining to a given element and usually sits above the element symbol. (On the chart we're using, in fact, no other numbers are listed.) The atomic number is the number of protons in a single atom of that element.
Os is number 76, meaning one atom of osmium has 76 protons. , This number is usually found beneath the atomic symbol.
Note that the chart in this example is based solely on atomic number and doesn’t list the atomic weight.
This won’t always usually be the case.
Osmium has an atomic weight of
190.23. , In our example,
190.23 would be rounded to 190, resulting in an atomic mass of 190 for osmium. , Since the vast majority of an atom’s mass is found its protons and neutrons, subtracting the number of protons (i.e. the atomic number) from the atomic mass will give you the calculated number of neutrons in the atom.
The numbers after the decimal point represent the usually very small mass of the electrons in the atom.
In our example, this is: 190 (atomic weight) – 76 (number of protons) = 114 (number of neutrons). , To find the number of neutrons in the future, simply use this formula:
N = M – n N = number of Neutrons M = atomic Mass n = atomic number
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