Calculating the number of neutrons in an atom or an isotope is quite simple and does not require any kind of experimentation: just follow the instructions in this guide.
Steps
Method 1 of 2: Finding the Number of Neutrons in a Regular Atom
Step 1. Find the position of the element on the periodic table
In our example, we will consider osmium (Os), which is found in the sixth row below.
Step 2. Find the atomic number of the element
It is usually the most visible number, written above the symbol of the element itself - in our table above it is the only number shown. The atomic number represents the number of protons in a single atom of the element under consideration.
The number for Hos is 76; this means that an osmium atom has 76 protons.
Step 3. Find the atomic weight of the element
This number is usually found written under the atomic symbol. Note that the diagram shown here contains only the atomic numbers and not the atomic weights of the elements. Usually, however, this is not the case. Osmium has an atomic weight of 190.23.
Step 4. Approximate the atomic weight to the nearest whole number; this will give you the atomic mass
In our example, 190, 23 will be approximated to 190, giving an atomic mass for osmium equal to 190.
Step 5. Subtract the atomic number from the atomic mass
Since for most atoms, mass is given by protons and neutrons, subtracting the number of protons (which is the atomic number) from the atomic mass, you will get the "calculated" number of neutrons of an atom. In our case, it will be: 190 (atomic weight) - 76 (number of protons) = 114 (number of neutrons).
Step 6. Learn the formula
In the future, to find the number of neutrons, simply use this formula:
-
N = M - n
- N = number of No.eutrons
- M = M.atomic assa
- n = atomic number
Method 2 of 2: Finding the Number of Neutrons in an Isotope
Find the Number of Neutrons in an Atom Step 7 Step 1. Find the position of the element on the periodic table
As an example, we will look at the carbon-14 isotope. Since the non-isotopic form of carbon-14 is simply carbon (C), find carbon in the periodic table.
Find the Number of Neutrons in an Atom Step 8 Step 2. Find the atomic number of the element
It is usually the most visible number, written above the symbol of the element itself - in our table above it is the only number shown. The atomic number represents the number of protons in a single atom of the element under consideration.
The number for C is 6; this means that a carbon atom has 6 protons.
Find the Number of Neutrons in an Atom Step 9 Step 3. Find the atomic mass
This is a no-brainer with isotopes, as their name comes precisely from their atomic mass. Carbon-14, for example, has an atomic mass of 14. Once the atomic mass of the isotope has been found, the procedure is the same as that used to find the number of neutrons in a regular atom.
Find the Number of Neutrons in an Atom Step 10 Step 4. Subtract the atomic number from the atomic mass
Since for most atoms, mass is given by protons and neutrons, subtracting the number of protons (which is the atomic number) from the atomic mass, you will get the "calculated" number of neutrons of an atom. In our case, it will be: 14 (atomic mass) - 6 (number of protons) = 8 (number of neutrons).
Find the Number of Neutrons in an Atom Step 11 Step 5. Learn the formula
In the future, to find the number of neutrons, simply use this formula:
-
N = M - n
- N = number of No.eutrons
- M = M.atomic assa
- n = atomic number
Advice
- Osmium, a metal in a solid state at room temperature, derives its name from the Greek word "osme", which means odor.
- Protons and neutrons determine the weight of elements, while electrons and other particles have negligible mass (close to zero mass). Since a proton weighs approximately as much as a neutron and since the atomic number represents the number of protons, we can simply subtract the number of protons from the total mass.
- If you happen to be unsure what the various numbers of the periodic table represent, remember that the table is organized according to the atomic number (which is the number of protons), starting from 1 (hydrogen) and increasing one unit at a time from left to right, ending with 118 (ununoctio). This is because in an atom the number of protons determines the type of atom; that's why it's the easiest feature to use when organizing the various elements. (For example, an atom with 2 protons will always be helium, just as an atom with 79 protons will always be gold).
