Although all atoms of the same element contain the same number of protons, their number of neutrons can vary. Knowing the number of neutrons in an atom can help you determine if it is a normal atom of that element or an isotope, which will have additional or fewer neutrons. Identifying the number of neutrons in an atom is very simple and does not even require any experimentation. To calculate the number of neutrons in a normal atom or isotope, all you will have to do is follow these instructions with a periodic table at hand.
Steps
Method 1 of 2: Finding the Number of Neutrons in a Normal Atom
Step 1. Locate the element on the periodic table
For this example, we will use osmium (Os), which is in the sixth row from the bottom.
Step 2. Find the atomic number of the element
It tends to be the most visible number belonging to a given element and is usually found above the element's symbol. In the example table, in fact, there are no more numbers listed. The atomic number is the number of protons in a single atom of that element. Os is the number 76, which means that an osmium atom has 76 protons.
The number of protons never changes in an element; this is basically what said element makes it
Step 3. Find the atomic weight
This number is usually found below the atomic symbol. Note that the example graph is based on atomic number only and does not show atomic weight. But it will not always be the case. Osmium has an atomic weight of 190.23.
Step 4. Round the atomic weight to the nearest whole number to find the atomic mass
In this example, 190, 23 rounds to 190, resulting in an atomic weight of 190 for osmium.
The atomic weight is an average of the isotopes of the element, so it is not usually a whole number
Step 5. Subtract the atomic number from the atomic mass
Since the vast majority of the atomic mass is found in protons and neutrons, subtracting the number of protons (for example the atomic number) from the atomic mass will give the calculated value of the number of neutrons in the atom. The numbers after the decimal point represent the normally very small mass of electrons in the atom. In the example, this is: 190 (atomic weight) - 76 (number of protons) = 114 (number of neutrons).
Step 6. Remember the formula
To find the number of neutrons in the future, just use this formula:
-
N = M - n
- N = number of Neutrons
- M = Matomic handle
- n = atomic number
Method 2 of 2: Finding the Number of Neutrons in an Isotope
Step 1. Locate the element on the periodic table
As an example, the isotope of carbon-14 will be taken. Since the non-isotopic form of carbon-14 is simply carbon (C), you will find carbon on the periodic table in the second column below.
Step 2. Find the atomic number of the element
It is usually the most visible number belonging to a given element and is usually found above the element symbol. In the example table, in fact, there are no more numbers listed. The atomic number is the number of protons in a single atom of that element.
C is the number 6, which means that a carbon atom has 6 protons.
Step 3. Find the atomic mass
It's really easy with isotopes, since they are named according to their atomic mass. For example, carbon-14 has an atomic mass of 14. Once you find the atomic mass of the isotope, the process is the same as for finding the neutrons in a normal atom.
Step 4. Subtract the atomic number from the atomic mass
Since the vast majority of the atomic mass is found in protons and neutrons, subtracting the number of protons (for example the atomic number) from the atomic mass will give the calculated value of the number of neutrons in the atom. In the example, this is: 14 (atomic weight) - 6 (number of protons) = 8 (number of neutrons).
Step 5. Remember the formula
To find the number of neutrons in the future, just use this formula:
-
N = M - n
- N = number of Neutrons
- M = Matomic handle
- n = atomic number
Advice
- The name of osmium, a metal that is solid at room temperature, derives from the Greek word for odor, "osme."
- Protons and neutrons make up almost all the weight of the elements while electrons and various other particles make up almost zero of their mass (practically zero mass). Since a proton has approximately the same weight as a neutron and the atomic number represents the number of protons, the number of protons can simply be subtracted from the total mass.
- If you are not sure what number each is in the periodic table, just remember that the table is designed based on the atomic number (for example, the number of protons), start with 1 (hydrogen) and add one unit at a time from left to right, ending with 118 (ununoctium). This is because the number of protons in an atom determines what that atom is, making it the easiest elemental trait to organize. For example, an atom with 2 protons will always be helium, just as an atom with 79 protons will always be gold.