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How well do you remember how to determine the number of valence electrons a representative element has?

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Recall that valence electrons are electrons located in the valence shell, or outermost energy level, of an atom.

In this model of a sodium atom, you can see that a sodium atom has 11 electrons, with only one electron in its highest energy level. So, sodium has one valence electron.

This can also be determined using its shortened electron configuration.

[Ne]3s1 (the valence electron is the one electron in the 3s sublevel).

electron structure of sodium

Another way to determine the number of valence electrons an element has is by noting its position on the periodic table.

Recall that the elements in Groups 1-2 and 13-18 are often referred to as the representative elements, or main group elements. A representative element's group number and the number of valence electrons its atoms contain are related. Click the periodic table to review what you have learned about this relationship.

Periodic table with labels: Enter key opens full-screen view with caption; escape key exits full screen.
Periodic table with labels. Full description in following section.

Periodic table with the following labels:

  • Group 1 labelled 1

  • Group 2 labelled 2

  • Group 13 labelled 3

  • Group 14 labelled 4

  • Group 15 labelled 5

  • Group 16 labelled 6

  • Group 17 labelled 7

  • Group 18 labeled 8

This periodic table shows how a representative element's group number and the number of valence electrons its atoms contain are related.

All elements in each group have the same number of valence electrons. The Group 1 elements have one valence electron, the Group 2 elements have two valence electrons, and so on. Since sodium is in Group 1, we know that a sodium atom has one valence electron.

Note that all the Group 18 elements have eight valence electrons, except for helium (He), which has only two valence electrons. This is because helium only contains one subshell, which can hold a maximum of two electrons.

Let's Practice

Do you remember how to determine the number of valence electrons a representative element contains? Find out by completing this activity. Use the periodic table to match each element on the left with the correct number of valence electrons on the right.

If you need a periodic table, click below to open an interactive periodic table or to download a PDF.

Periodic Table PDF

To match items, click or tap an item in the left column and then click or tap its match in the right column. If you change your mind, make a different choice. Once you have matched all items, click "Check Answers" to see how you did. Click "Reset" to try again.
Great job!