Question 6.1: Writing Ground-State Electron Configurations for Ions Predic...
Writing Ground-State Electron Configurations for Ions
Predict the ground-state electron configuration for each of the following ions.
STRATEGY
First write the electron configuration for the atom. To account for charge of the ion, add electrons for anions and remove electrons for cations. Remember transition metal cations lose outer shell s electrons before d electrons.
(a) The valence electron configuration for Se is [Ar] 4s² 4p^{4} Add two electrons to form the Se^{2-} ion:
Se: [Ar] 4s²4p^{4} \overset{+2e^{-}}{→}Se^{2-} : [Ar] 4s²4p^{6} or [K](b) The electron configuration for Cs is [Xe] 6s¹ . Remove one electron to form the Cs^{+} ion:
Cs: [Xe] 6s¹ \overset{-e^{-}}{→} Cs^{+}: [Kr] 5s² 5p^{6} or [Xe](c) The electron configuration for Cr is [Ar] 4s¹ 3d^{5} . Three electrons must be removed to form Cr^{3+}. First remove one electron from the 4s orbital and then two electrons from the 3d orbitals to form the Cr^{3+} ion:
Cr: [Ar] 4s¹ 3d^{5} \overset{-3e^{-}}{→} Cr^{3+}: [Ar] 3d^{3}