How to Calculate the Number of Electrons

All basic elements are made up of electrons, protons, and neutrons. Electrons are negatively charged particles that make up part of an atom. Determining the number of electrons in an atom is a fundamental skill in chemistry. This is very easy if you know how to use the periodic table. Besides, other skills that are equally important are calculating the number of neutrons and valence electrons (the number of electrons in the outermost shell) of an element.

Table of Contents

Calculate the number of electrons in a neutral atom

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Have a periodic table of chemical elements ready. This table consists of many color-coded cells that rely on atomic structure to arrange all known elements. The name of each element is listed with 1, 2 or 3 initials, followed by the atomic mass and atomic number. ^{[1] X Research Source}

You can easily find the periodic table in textbooks or online.

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Find the element mentioned in the periodic table . The elements are arranged by atomic number and are classified into three main groups: metals, nonmetals, and nonmetals. These elements are further divided into subgroups including alkali metals, halogens and noble gases. ^{[2] X Research Source} Each column in the table is called a group and each row is a period.

If you know more information about the element (such as the group or period) it will be easier to identify.
If you don’t have any information about the element you’re looking for, just look for that symbol in the periodic table.

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Find the atomic number of the element. In each square, the atomic number is in the upper left or middle corner above the element symbol. The atomic number is the number of protons in the nucleus of an atom. ^{[3] X Research Source} Protons are positively charged particles that make up atoms. Because electrons are negatively charged, an element in the neutral state will have the same number of protons and electrons.

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

Calculate the number of electrons in a positive/negative ion

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Determine the charge of the ion. If an atom gains or loses electrons, it will not change in nature, but only in charge. Then we will have an ion, such as K ⁺ , Ca ²⁺ or N ^3- . Usually, charge is shown in small letters at the top right of the element’s symbol.

Electrons are negatively charged particles, so when an atom gains an electron, the atom becomes a negative ion.
Conversely, when it loses an electron, the atom becomes a positive ion.
For example, N ^3- has a charge of -3, and Ca ²⁺ has a charge of +2.

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

For example, Ca ²⁺ has a charge of +2, which indicates that the atom has lost 2 electrons from its electrically neutral state. The atomic number of calcium is 20, so the Ca ²⁺ ion has 20 – 2 = 18 electrons.

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Add the atomic number to the charge if the ion is negative. For the negative charge case, the ion has gained an extra electron. To determine the number of electrons available, calculate the sum of the charge and the atomic number. 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 indicates that the nitrogen atom has gained 3 more electrons than the neutral state. The atomic number of nitrogen is 7, so the N ^3- ion has 7 + 3 = 10 electrons.

Steps

Calculate the number of electrons in a neutral atom

Calculate the number of electrons in a positive/negative ion

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