To find the number of neutrons in an atom, use this formula:
Number of neutrons=Mass number−Atomic number\text{Number of neutrons}=\text{Mass number}-\text{Atomic number}Number of neutrons=Mass number−Atomic number
- The atomic number (number of protons) is found on the periodic table above the element's symbol.
- The mass number is the total of protons and neutrons, often found as a whole number associated with the isotope of the element.
- Subtracting the atomic number from the mass number gives the number of neutrons.
For example, if an atom has an atomic number of 17 and a mass number of 37, the number of neutrons is:
37−17=2037-17=2037−17=20
The atomic number equals the number of protons, and for a neutral atom, the number of electrons equals the atomic number as well.
