Behavior in Non-Standard Oxidation States

While $$+3$$ is the default baseline for both series, specific elements deviate to achieve stability:

• Reducing Agents ($$+2 \rightarrow +3$$): $$\text{Eu}^{2+}$$ ($$f^7$$) and $$\text{Yb}^{2+}$$ ($$f^{14}$$) are highly stable in the $$+2$$ state but readily oxidize to the baseline $$+3$$ state.
• Oxidizing Agents ($$+4 \rightarrow +3$$): $$\text{Ce}^{4+}$$ ($$f^0$$) intensely acts to gain an electron to drop back down to its stable $$+3$$ baseline state.