How to Calculate the Number of Protons, Neutrons and Electrons

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This article was co-written by Meredith Juncker, PhD. Meredith Juncker is a PhD student in Biochemistry and Molecular Biology at Louisiana State University’s Center for Health Sciences. Her studies focus on proteins and neurodegenerative diseases.

This article has been viewed 171,597 times.

This article will show you how to calculate the number of protons, neutrons, and electrons as well as how to calculate the number of these particles when an atom is ionized.

Table of Contents

Calculate the number of protons, neutrons and electrons

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Prepare the periodic table of chemical elements. The periodic table of the chemical elements (referred to as the periodic table) is a table that arranges the elements according to their nuclear structure. In the periodic table, the elements are usually divided by color and have a shortened chemical symbol consisting of 1, 2, and 3 letters. Other information about the element mentioned in the periodic table is its atomic mass and atomic number. ^{[1] X Research Source}

The periodic table is often included with textbooks, which you can also find online or buy in bookstores.
During the test, some teachers may give a periodic table.

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Locate the element you want to find in the periodic table. The periodic table sorts elements by atomic number and divides them into three main groups: metals, nonmetals, and nonmetals. There are also groups of alkali metals, halogens and noble gases. ^{[2] X Research Source}

Use groups (columns) or periods (rows) to locate the element of interest in the periodic table.
You can also search for elements by chemical symbol if you don’t know anything more about that element.

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Locate element by atomic number. The atomic number is usually written in the upper left corner of the element’s chemical symbol. The atomic number provides information about the number of protons constituting an atom of that element. ^{[3] X Research Sources}

For example, Bo(B) has an atomic number of 5, which means that the atom of this element has 5 protons.

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Determine the number of electrons. Proton is a positively charged particle located in the nucleus. Electrons are negatively charged particles. Therefore, an element that is electrically neutral will have an equal number of protons and electrons.

For example, Bo(B) has an atomic number of 5, which means that the atom of this element has 5 protons and 5 electrons.
However, if the element has a positive ion or a negative ion, the number of protons and the number of electrons will not be equal. At this point, you need to make the necessary calculations to determine the amount of each type of seed. The number of ions is expressed as a small digit in the upper right (like the exponent) of the element.

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Find the atomic mass of the element. To calculate the number of neutrons, you first need to determine the atomic mass of the element. The atomic mass of an element (also the atomic mass of the element) is the average mass of the atoms of an element. ^{[4] X Research Source} The mass number is usually written just below the element’s chemical symbol.

You need to round the atomic mass. For example, Bo’s atomic mass is 10,811, to calculate the number of neutrons you can round to 11.

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Subtract the atomic number from the atomic mass. The number of neutrons is calculated as the difference between the atomic mass and the atomic number. You need to remember that the atomic number is equivalent to the number of protons, which was determined in the previous step. ^{[5] X Research Sources}

In the example of the element Bo, we have the number of neutrons calculated as: 11 (atomic mass) – 5 (atomic number) = 6 neutrons.

Calculate the number of electrons in an ionized atom

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Determine the number of ions. The number of ions in an ionized atom is expressed as one (or several) small digits in the upper right of the element. An ion is a particle with a negative or positive charge depending on its ability to donate/accept electrons. ^{[6] X Research Source} The number of protons in an atom is a constant, only the number of electrons changes when the ionized atom becomes an ion.

Electrons are negatively charged particles, so when an atom lacks electrons, the atom becomes a positive ion. Conversely, when an atom gains more electrons, the atom becomes a negative ion.
For example, N ^3- has a charge of -3, and Ca ²⁺ has a charge of +2.
Remember that if the atom doesn’t have an ion digit in the upper right, you don’t need to calculate this step.

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For positive ions, subtract the charge from the atomic number. When an ion has a positive charge, the atom of that ion has lost electrons. To calculate the number of electrons remaining, you subtract the charge of the ion from the atomic number. In the case of positive ions, the number of protons will be greater than the number of electrons.

For example, Ca ²⁺ has a charge of +2, which means it has lost 2 electrons from its neutral state. The atomic number of calcium is 20, so the Ca ²⁺ ion has 18 electrons.

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Add the atomic number to the charge in the case of negative ions. An atom with an extra electron will form a negative ion. To calculate the total number of electrons in that ion, you simply take the atomic number plus the residual charge. In this case, the number of protons will be less than the number of electrons.

For example, N ^3- has a charge of -3, which means that the nitrogen atom has gained 3 more electrons compared to the charge-neutral state. The atomic number of nitrogen is 7, so the N ^3- ion has 7 + 3 = 10 electrons.

Steps

Calculate the number of protons, neutrons and electrons

Calculate the number of electrons in an ionized atom

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