Figuring out information about the valence shell of an element is an important skill taught in high school chemistry. The electrons in the outermost shell of an atom are called its valence electrons. These valence electrons control how an element will react with other chemicals. Noble gases have a complete valence shell and are the most chemically nonreactive. Elements that only have one electron in their valence shell or are missing one electron from having a complete shell are the most reactive. For most elements you can use the periodic table groups to ascertain information about an element's valence shell.
- Skill level:
- Easy
Instructions
Things you need
- Periodic Table
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1
Locate the element you are examining on the periodic table. Most elements are listed by initials that correspond to part of the element's name, such as He for Helium and O for oxygen.
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2
Count the periodic table group columns going from the left to the right until you reach the column with your element. The groups may be listed from 1A to 8A or from 1 to 18. For example, oxygen is in group 16 or 6A and lithium is in group 1 or 1A.
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3
Use the element's periodic table group to determine how many electrons are in its valence shell. Groups 1 and 2 have a number of electrons in their valence shell equal to their group number. For elements in groups 13 through 18, they have a number of electrons in their valence shell equal to "group number minus 10." If the groups are ordered 1A to 8A, you don't need to subtract. For example, oxygen, which is in group 16, has "16-10 = 6" valence electrons. One exception is helium, which is in group 18 but only has two valence electrons. For the transition elements, groups 3 to 12, valence electrons can't be determined in a predictable, reliable way. This is because electrons move into the sub levels and complicate the electron configuration.
