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How can the periodic table be used to determine the valence electrons of an element?

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Earlier in this lesson, you reviewed how to determine the number of valence electrons an element has based on its electron configuration. The number of valence electrons can also be determined by the location of the element on the periodic table. Click the periodic table to review this relationship.

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

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 labelled 8

Look at this periodic table. Recall that when the representative elements are numbered from 1 through 8, the group number then matches the number of valence electrons in that group.

All elements in each group have the same number of valence electrons. Elements in the first group (alkali metals) have one valence electron, those in the second group (alkaline earth metals have two valence electrons, and those in group 13 have three valence electrons. The number of valence electrons continues to increase until reaching group 18, which has eight valence electrons, except for helium, which can only hold a maximum of two electrons.

Since the elements in each group have the same valence electrons, that means that they have similar properties. The elements in the alkali metals with only one valence electron are very reactive, thus the reactions between sodium and water and potassium and water are seen.

icon with book and keyboard

Let's Practice

Using this information, match the element on the left with its 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!

Reflection

How does the number of valence electrons of sodium and potassium explain the reactions they have with water?