Electrons are negatively charged particles that make up part of an atom. All basic elements are composed of electrons, protons, and neutrons. The basic concept in chemistry is the ability to find the number of electrons present in an atom. Using the periodic table of elements, the number of electrons can be found easily. Other important concepts include finding the number of neutrons and valence electrons (the number of electrons in their outermost shell) in an element.
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Method 1 of 2: Finding the Number of Electrons in a Neutral Atom
Step 1. Find the periodic table of the elements
The periodic table is a color-coded table that lists all the known elements based on their atomic structure. Each element has an abbreviation consisting of 1, 2, or 3 letters and is written along with its weight and atomic number.
The periodic table can be easily searched in chemistry books or online
Step 2. Find the element in question on the periodic table
Elements are arranged by atomic number and separated into three main groups: metals, nonmetals, and metalloids (semimetals). These elements are further classified into specific groups including the alkali metals, halogens, and noble gases. Each column in the table is called a group and each row is called a period.
- If you know the details of your element such as its group or period, you can find it more easily.
- If you don't know anything about the element in question, look up its symbol in the table until you find it.
Step 3. Find the atomic number of an element
The atomic number is in the upper-left corner, above the element symbol in the box. The atomic number indicates the number of protons present in an element. Protons are particles in an element that have a positive charge. Since electrons have a negative charge, when an element is in a neutral state, the element has the same number of protons and electrons.
For example, boron (B) has an atomic number of 5. That is, it has 5 protons and 5 electrons
Method 2 of 2: Finding the Number of Electrons in a Positive/Negatively Charged Ion
Step 1. Find the charge of the ion
The addition or removal of electrons from an atom does not change its identity, but changes its charge. In this case, you now have an ion like K+, Ca2+, or N3-. Usually, charge is denoted as a small number to the right of the atomic symbol.
- Since electrons have a negative charge, as you add electrons, the ion becomes more negative.
- As you lose electrons, the ions become more positive.
- For example, N3- has a -3 charge, while Ca2+ has a charge of +2.
Step 2. Subtract the charge from its atomic number if the ion has a positive charge
If the charge is positive, the ion loses electrons. To find the number of electrons left, subtract the total charge from the atomic number. In this case, there are more protons than electrons.
For example, Ca2+ has a +2 charge so the ion has 2 fewer electrons than a neutral calcium atom. The atomic number of calcium is 20 so this ion has 18 electrons.
Step 3. Add charge to the atomic number if the charge is negative
If the charge is negative, the ion gains electrons. To find the number of electrons, add the total charge to the atomic number. In this case, there are fewer protons than electrons.
For example, N3- has a charge of -3. That is, the atom has 3 more electrons than the neutral nitrogen atom. The atomic number of nitrogen is 7 so this ion has 10 electrons.
Related wikiHow Articles
- Finding Valence Electrons
- Finding the Number of Neutrons in an Atom
- Finding the Number of Protons, Neutrons, and Electrons
