Electron Configurations of Ions:
When electrons are removed from an atom to form a cation, they are always removed first from the occupied orbitals having the highest principal quantum number, n.
Removing one electron from a lithium atom produces:
When electrons are added to an atom to form an anion, they are added to the empty or partially filled orbital having the lowest value of n.
Li (1s22s1) − e− ⇒ Li+ (1s2)
Removing two electrons from an iron atom produces:
Fe ([Ar]3d64s2) − 2e− ⇒ Fe+2 ([Ar]3d6)
Removing an electron from Fe+2 produces:
Fe+2 ([Ar]3d6) − e− ⇒ Fe+3 ([Ar]3d5)
Adding one electron to a fluorine atom produces:
F (1s22s22p5) + e− ⇒ F− (1s22s22p6)
Electron Configurations and Orbital Diagrams