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# How do electron configurations change for ions?

When you create an ion, you are either adding electrons to, or removing electrons from, the highest occupied energy subshell in the atom.

**NONMETALS**

Write the electronic structure for the neutral atom.

Then add electrons to the highest occupied subshell.

E.g., for ##"Cl"^"-"##:

##"Cl": "1s"^2 "2s"^2 "2p"^6 "3s"^2 "3p"^5##, but ##"Cl"^"-"## has one more electron

Add it to the 3##p## subshell.

##"Cl"^"⁻": "1s"^2 "2s"^2 "2p"^6 "3s"^2 "3p"^6##

**##"s"## and ##"p"## BLOCK METALS**

Write the electronic structure for the neutral atom. Then remove electrons from the highest

For ##"Na"^+##:

##"Na": "1s"^2 "2s"^2 "2p"^6 "3s"##, but ##"Na"^+## has one less electron

Take it from the ##"3s"## subshell.

##"Na"^+: "1s"^2 "2s"^2 "2p"^6##

**##"d"## BLOCK METALS**

Remove ##"s"## electrons before ##"d"## electrons.

E.g., for ##"Cr"^(3+)##

##"Cr": "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6 "4s""3d"^5##

##"Cr"^(3+): "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6 "3d"^3##

You remove the ##"4s"## electron first, followed by two of the ##"3d"## electrons.

**EXAMPLES**

Write the electron configurations for ##"O"^"2-", "Ca"^(2+)##, and ##"Zn"^(2+)##.

**Solutions**

##"O": "1s"^2 "2s"^2"2p"^4##

##"O"^"2-": "1s"^2 "2s"^2"2p"^6##

##"Ca": "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6 "4s"^2##

##"Ca"^(2+): "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6##

##"Zn": "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6 "4s"^2"3d"^(10)##

##"Zn"^(2+): "1s"^2 "2s"^2"2p"^6 "3s"^2"3p"^6 "3d"^(10)##