How to Find the Number of Protons, Neutrons, and Electrons

This article was co-authored by Meredith Juncker, PhD. Meredith Juncker is a PhD candidate in Biochemistry and Molecular Biology at Louisiana State University Health Sciences Center. Her studies are focused on proteins and neurodegenerative diseases.

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Finding the number of protons, neutrons, and electrons in a given element isn't as hard as it sounds. Oftentimes part of your answer will be right in front of you in the periodic table! Once you know where to look, finding the number of protons, neutrons, and electrons will be a breeze.

Calculating Protons, Electrons, and Neutrons

• You can find a periodic table online or in a chemistry book.
• In tests, normally, a periodic table will be provided.

Step 2 Find your element on the periodic table." width="460" height="345" />

• Using the group (columns) or period (rows) can make the element easier to locate on the table.
• You can also search the table for the symbol of the element if you don’t know any other properties.

• For example, boron (B) has an atomic number of 5, therefore it has 5 protons.

• For example, boron (B) has an atomic number of 5, therefore it has 5 protons and 5 electrons.
• However, if the element includes a negative or positive ion, then the protons and electrons will not be the same. You will have to calculate them. The ion number will appear as a small superscript after the element.

• Make sure that you round the atomic mass to the nearest whole number. For example, the atomic mass of boron is 10.811, but you can just round the atomic mass up to 11.

• For our boron example, 11 (atomic mass) – 5 (atomic number) = 6 neutrons

Calculating the Electrons with Ions Present

• Because an electron has a negative charge, when you remove electrons, the ion becomes positive. When you add more electrons, the ion becomes negative.
• For example, N 3- has a -3 charge while Ca 2+ has a +2 charge.
• Keep in mind that you do not have to do this calculation if there is no superscripted ion number following the element.

• For example, Ca 2+ has a +2 charge so it has lost 2 electrons from the neutral state. Calcium’s atomic number is 20, therefore the ion has 18 electrons.

• For example, N 3- has a -3 charge; therefore, it has gained 3 electrons compared to the neutral state. Nitrogen’s atomic number is 7, therefore this ion has 10 electrons.

Expert Q&A

Meredith Juncker is a PhD candidate in Biochemistry and Molecular Biology at Louisiana State University Health Sciences Center. Her studies are focused on proteins and neurodegenerative diseases.

The number of protons will never change. Atoms with negative or positive charges just indicate a gain or loss of electrons.

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Meredith Juncker is a PhD candidate in Biochemistry and Molecular Biology at Louisiana State University Health Sciences Center. Her studies are focused on proteins and neurodegenerative diseases.

You will find actinium in group 3, period 7 of the periodic table. The atomic number of actinium is 89, which means there are 89 protons. Because there is no net charge, we know that # protons = # electrons, so there are 89 electrons as well.

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All the protons are present in the nucleus, or centre of an atom. You need the atomic number to find the amount of protons and/or electrons, unless you have the amount of neutrons and the atomic mass, in which case you can simply subtract the amount of neutrons from the atomic mass, leaving the amount of protons in the atom. The atomic number (number at the top) is the amount of protons and the amount of electrons. So if an element has an atomic number of 5, you know that it has 5 protons and 5 electrons. The atomic mass (number at the bottom) is the amount of protons and neutrons added together. Whichever you know, you subtract from the atomic mass.

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