Name a member of the lanthanoid series: (I) which exhibits +4 oxidation state; (II) which exhibits +2 oxidation state.
Show Hint
Lanthanoids most commonly show the +3 oxidation state, but a few show +2 or +4 when doing so gives an empty, half-filled, or fully-filled 4f subshell, which is extra stable.
Step 1: Recall the usual state. Lanthanoids almost always show the \(+3\) oxidation state.
Step 2: Know why other states appear. A \(+2\) or \(+4\) state shows up when it gives an empty \((4f^0)\), half-filled \((4f^7)\), or fully filled \((4f^{14})\) subshell, which is extra stable.
Step 3: Find the \(+4\) member. Cerium can lose four electrons to reach \(4f^0\) (empty subshell), so it shows the \(+4\) state.
Step 4: Find the \(+2\) member. Europium can stop at \(+2\) because that leaves a half-filled \(4f^7\) subshell, which is stable.
Step 5: State the answers. So Ce gives \(+4\) and Eu gives \(+2\).