Menu Close

Ions and Charge

Ions and isotopes are essential concepts in chemistry that help us understand the properties and behavior of elements. An ion is an atom or molecule that has lost or gained one or more electrons, resulting in a net electric charge. In contrast, an isotope is an atom of the same element with the same number of protons but a different number of neutrons. Understanding the differences between ions and isotopes is crucial in fields such as medicine, environmental science, and materials science.


If you recall, protons have a positive (+1) charge and electrons have a negative (-1) charge. Atoms have the same number of protons and electrons resulting in a net charge of zero.

For example, an atom Boron has an atomic number of 5, so it has 5 protons and 5 electrons.

When Boron ionizes, it has a charge of +3. Since the charge is positive, that means there are more protons than electrons. The three indicates there are 3 more protons than electrons.

Boron Ion (+3 charge)

When Fluorine ionizes, it has a charge of -1. Since the charge is negative, that means there are more electrons than protons. The one indicates there are 1 more electron than proton.

Fluorine Ion (-1 charge)

Determining the Charge of an Ion

The charge of an ion can be determined by its location on the Periodic Table. To fully understand why an ion ionizes with a particular charge, you need to understand the concept of valence electrons.

The charges for elements are listed in the table below:

Group 1+1
Group 2+2
Group 13+3
Group 14+4 / -4
Group 15-3
Group 16-2
Group 17-1
Group 180
Charges of Ions by Group Number

If you noticed, groups 3-12 were excluded from the table. Elements in those groups can have different charges depending on what they’re bonded to. There are also some exceptions in groups 13-16.