How to Find the Number of Protons, Neutrons and Electrons

2024 Author: Samantha Chapman | [email protected]. Last modified: 2024-01-15 13:47

Protons, neutrons and electrons are the three main particles that make up an atom. Just as their names suggest, protons have a positive charge, electrons have a negative charge, and neutrons have a neutral charge. The mass of electrons is very small, while that of neutrons and protons is practically identical. To find the number of electrons, protons and neutrons of an atom just use the information you find on the periodic table of the elements.

Steps

Part 1 of 2: Finding the Number of Protons, Electrons and Neutrons

Step 1. Get a periodic table of elements

It is a table that organizes the elements according to their atomic structure. It follows a color-based criterion and assigns each element a symbol consisting of one, two or three letters. The other information highlighted are the atomic weight and the atomic number.

You can find a copy online or in chemistry textbooks

Step 2. Find the element you are studying on the periodic table

The elements are arranged following the order of atomic number and are separated into three main families: metals, non-metals and metalloids (or semi-metals). A further subdivision can be made into alkali metals, halogens and noble gases.

• Using the groups (the columns) and the periods (the rows) of the table, you can find the element that interests you without any difficulty.
• If you don't know the other properties of the element, you can search by symbol.

Step 3. Find the atomic number

It is shown in the element box, in the upper left corner and indicates the number of protons present in a single atom of the element.

For example, boron (B) has an atomic number of 5, so it has 5 protons

Step 4. Determine the number of electrons

Protons are positive particles that contribute to the formation of the nucleus. Electrons, on the other hand, are negatively charged particles. Consequently, an atom under neutral conditions will have the same number of protons and electrons.

• For example, boron (B) has an atomic number of 5, so it has 5 protons and 5 electrons.
• However, if the element includes a positive or negative ion, then protons and electrons will not be in equal measure and you will need to calculate their number. Electric charge is indicated with a small superscript number after the element symbol.

Step 5. Find the atomic mass of the element, you will need it in order to calculate the number of electrons

This value (also called atomic weight) indicates the average mass of the atoms of an element, calculated using the relative abundance of the isotopes. You can find this number under the element symbol inside its box.

Make sure you round the atomic mass value to the nearest whole number. For example, the atomic mass of boron is 10.811 and you can round to 11

Step 6. Subtract the atomic number from the mass number

Since electrons have a very small mass, most of the mass of an atom is given by that of protons and neutrons. You can know the number of protons thanks to the atomic number and you just need to subtract this value from the mass number to find the number of neutrons.

Always considering the example of boron: 11 (mass number) - 5 (atomic number) = 6 neutrons

Part 2 of 2: Finding the number of Electrons from the Ions

Step 1. Determine the number of ions

This value is indicated with a small number in superscript after the element symbol. An ion is an atom that has a positive or negative charge due to the addition or subtraction of electrons. Although the number of protons and neutrons remains constant, in this case the number of electrons changes.

• Since electrons are negatively charged, when you remove them you get a positive ion. When you add electrons, you generate a negative ion.
• For example, N^3- possesses charge -3 while Ca²⁺ has a +2 charge.
• Keep in mind that there is no need to calculate if there is no superscript number after the element.

Step 2. Subtract the charge from the atomic number

When an ion has a positive charge, the atom has lost electrons. To calculate the number of the remaining ones, you need to subtract the value of the extra charge from the atomic number. In the case of a positive ion, there are more protons than electrons.

For example, Ca²⁺ it has +2 charge, so it has lost 2 electrons with respect to the atom in the neutral state. The atomic number of calcium is 20, so the ion has 18 electrons.

Step 3. Add the charge to the atomic number, if you are considering a negative ion

In this case you are faced with an atom that has gained electrons. To find the current number of electrons, simply add the absolute value of the charge to the atomic number. In negative ions, there are more electrons than protons.

For example, N^3- it has a -3 charge, so it has gained 3 electrons with respect to the same atom under neutral conditions. The atomic number of nitrogen is 7, so the ion has 10 electrons.