Determining the number of neutrons in an atom is quite simple and does not require any experience. To calculate the number of neutrons in an ordinary atom or isotope, simply follow these instructions.
Step
Method 1 of 2: Finding the Number of Neutrons in an Ordinary Atom
Step 1. Find the element in the periodic table
In this example, we will look at osmium (Os), in the sixth row.
Step 2. Find the atomic number of the element
This number tends to be the most visible number and is usually above the element symbol. (The table doesn't even show any other numbers.) The atomic number is the number of protons in a single atom of the element. Os is the number 76, which means one atom of osmium has 76 protons.
Step 3. Find the atomic mass of the element
This number is usually below the atomic symbol. Note that the table in this example is based on atomic number only and does not list atomic weights. This is usually not always the case. Osmium has an atomic weight of 190.23.
Step 4. Round the atomic weight to the nearest number to find the atomic mass
In this example 190, 23 is rounded up to 190, so the atomic mass of osmium is 190.
Step 5. Subtract the atomic number from the atomic mass
Since most of the atomic mass is found to be protons and neutrons, subtracting the number of protons (i.e. atomic number) from the atomic mass will give you the calculated number of neutrons in the atom. The numbers after the decimal point are usually the very small masses of electrons in an atom. In our example: 190 (atomic weight) - 76 (number of protons) = 114 (number of neutrons).
Step 6. Remember the formula
To find the number of neutrons, simply use this formula:
-
N = M – n
- N = number Neutron
- M = Matomic mass
- n = number of atoms
Method 2 of 2: Finding the Number of Neutrons in an Isotope
Step 1. Find the element in the periodic table
As an example, we will look at the isotope carbon-14. Since the non-isotope form of carbon-14 is carbon (C), look for the element carbon in the periodic table (in the second row).
Step 2. Find the atomic number of the element
This number tends to be the most visible number and is usually above the element symbol. (The table doesn't even show any other numbers.) The atomic number is the number of protons in a single atom of the element.
C is the number 6, which means one carbon atom has 6 protons.
Step 3. Find the atomic mass
For isotopes is very easy, because it is named according to the atomic mass of the element. Carbon-14, for example, has an atomic mass of 14. After finding the atomic mass of an isotope, the process is the same as finding the number of neutrons in an ordinary atom.
Step 4. Subtract the atomic number from the atomic mass
Since most of the atomic mass is found to be protons and neutrons, subtracting the number of protons (i.e. atomic number) from the atomic mass will give you the calculated number of neutrons in the atom. The numbers after the decimal point are usually the very small masses of electrons in an atom. In our example: 14 (atomic mass) - 6 (number of protons) = 8 (number of neutrons).
Step 5. Remember the formula
To find the number of neutrons, simply use this formula:
-
N = M – n
- N = number Neutron
- M = Matomic mass
- n = number of atoms
Tips
- Osmium, a metal that is solid at room temperature, derives its name from the Greek word for odor, "osme."
- Protons and neutrons make up almost all of the element's weight, while electrons and other particles make up a negligible mass (close to zero mass). Since a proton has almost the same weight as a neutron, and the atomic number is the number of protons, we can subtract the number of protons from the total mass.
- If you don't remember the element numbers in the periodic table, remember that the table is designed around the atomic number (i.e. the number of protons), starting with 1 (hydrogen) and increasing every unit from left to right, and ending at 118 (ununoctium). This is because the number of protons in an atom determines the atom, making it an easily manageable property of the element. (e.g. an atom with 2 protons must be helium, an atom with 79 protons must be gold.)
