Study Sheet for Writing Electron Configurations for Monatomic Ions

Study Sheet

Sample Study Sheet: Writing Electron Configurations for Monatomic Ions

Tip-off If you are asked to predict the charge or charges on monatomic ions of an element, or if you are asked to write abbreviated electron configurations for monatomic ions, follow these steps.

General Steps - To predict ionic charges, follow these guidelines.

Nonmetallic elements form anions.

Hydrogen atoms gain one electron to form H^- with a stable 1s² electron configuration.

The other nonmetallic elements gain one, two, or three electrons to achieve a stable ns²np⁶ configuration. The group 17 nonmetals form -1 ions, the group 16 nonmetals form -2 ions, and the group 15 nonmetals form -3 ions.

Metallic elements form cations. (You will only be able to predict some of the charges on these cations.)

Many elements lose one, two, or three electrons and achieve one or two of the stable electron configurations: 1s², ns²np⁶, nd¹⁰, or nd¹⁰(n+1)s².

The exact procedure for writing the abbreviated electron configuration for an ion depends on whether the ion is an anion; Al³⁺ or a cation in groups 1, 2, or 3; or any other cation.

For monatomic anions, follow these steps.

Locate the symbol for the element on the periodic table.

Move to the far right of the same row on the table to find the nearest larger noble gas.

Write the abbreviated electron configuration for this noble gas.

This can be done most simply by putting the symbol for this noble gas in brackets, For example, [Ar] for argon.

It can also be done using the symbol for the noble gas element at the end of the previous row. For example, [Ne] 3s² 3p⁶ for argon.

For Al³⁺ and monatomic cations from elements in groups 1, 2, or 3, follow these steps.

Locate the symbol for the element on the periodic table.
Move up one row and to the far right on the table to find the symbol for the noble gas to put in brackets.
Write the abbreviated electron configuration for this noble gas.

For any other monatomic cations, follow these steps.

Write the abbreviated electron configuration for the uncharged atom, listing the sublevels for the electrons outside of the noble gas configuration in the order of increasing principal energy level.
Remove electrons from the electron configuration of the uncharged atom starting with the electrons listed on the far right. Remove one electron for +1 cations, two electrons for +2, and three electrons for +3.

Click here to see an example.

Click here to see an exercise.

Return to the Monatomic Ion Configuratuions Page.