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The neutron number refers to the total number of neutrons in the nucleus. If the number of neutrons is larger than the number of protons, the atom has a neutron excess.
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Sign up for freeWhat is the neutron number?
Where is the neutron number in the nuclide notation?
Which data do you need to calculate the neutron number?
What is neutron excess?
What is a neutron?
Where are neutrons located?
What is another name for neutrons?
What is the effect of there being more neutrons in an atom?
What can happen when an atom has more neutrons than protons?
What happens when, due to an excess of neutrons, the atom breaks into smaller particles?
What is the neutron number?
Where is the neutron number in the nuclide notation?
Which data do you need to calculate the neutron number?
What is neutron excess?
What is a neutron?
Where are neutrons located?
What is another name for neutrons?
What is the effect of there being more neutrons in an atom?
What can happen when an atom has more neutrons than protons?
What happens when, due to an excess of neutrons, the atom breaks into smaller particles?
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Team Neutron Number Teachers
To identify the neutron number, you need to read the element’s nuclide notation. The neutron number is located in the lower right corner of the nuclide notation, as in this example of Iron 56:
\[^{56}_{26}Fe_{30}\]
However, the neutron number is not always specified and thus may need to be calculated.
Figure 1. Tritium, which is an isotope of hydrogen. Its nuclide notation indicates that there are three particles in the nucleus: one proton and two neutrons. Source: Manuel R. Camacho, StudySmarter.
To calculate the neutron number, use the nuclide notation as shown below:
\[\text{Neutron number} = (\text{Mass number - Atomic number})\]
In the case of Iron 56, this looks as follows
\(\text{Neutron number} = (56 - 26) = 30\)
The nuclide notation defines the number of particles in the nucleus in the upper-left corner, while the number of protons is given in the lower-left corner, as in this example of Iron 56:
\[^{56}_{26}Fe_{30}\]
Iron has 26 protons, as indicated by the atomic number in the lower-left corner, and a total of 56 particles in the nucleus, as shown in the upper-left corner. You might expect the number of protons and other particles in the nucleus to be equal, but that is not the case. Multiplying 26 by two would give you 52, whereas the atomic number 56 indicates that there are four additional particles in the atom’s nucleus. There is, therefore, a neutron excess of four.
An atom with either a lack or an excess of neutrons is called an isotope. Some isotopes break up after some time, which produces radiation in the form of particles such as photons, beta particles and others. There can be many isotopes for a single atomic element.
Figure 2. Hydrogen isotopes with different numbers of neutrons in the nucleus. From left to right: no neutron, one neutron, and two neutrons. Source Manuel R. Camacho, StudySmarter.
A neutron is a particle located in the centre of an atom alongside protons. Both neutrons and protons are also known as nucleons. Neutrons have a neutral charge and are one of two types of particles that contribute a greater amount of mass to an atom. The characteristics of neutrons are shown below:
| Particle | Mass in kilograms | Electrical charge in coulombs | Location |
| neutron | \(1.67 \cdot 10 ^{-27}\) | 0 | Nucleus |
Neutrons are one of two types of particles that make up most of an atom’s mass. The more neutrons an atom has, the heavier it is. Neutrons have a mass that is 1836.15 times larger than that of an electron and are just a bit heavier than protons.
Neutrons have a neutral electrical charge. Because of this, when an atom has a neutron excess, it does not change its electrical nature.
When thinking about atomic charges, it helps to work with the concept of relative charge. The relative electrical charge of a neutron is 0. A neutron’s relative charge is indicated as below:
\[0^n\]
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How do we determine the number of neutrons?
To determine the number of neutrons, you need to read the nuclide notation and apply the following formula:
Neutron number = Mass number-Atomic number.
What is the neutron number?
The neutron number indicates the number of neutrons in an atom.
What is neutron excess?
Neutron excess indicates that there are more neutrons than protons in the atom’s nucleus. It is determined by subtracting the number of protons from the number of neutrons.
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