Animated Solution for Chemistry - d and f-Block Elements: The highest possible oxidation states of uranium and plutonium, respectively, are

When we study the f-block elements, the lanthanoids often seem quite well-behaved, stubbornly sticking to their favorite $+3$ oxidation state. But the actinoids? They are the rebels of the periodic table. They exhibit a fascinating and wide variety of oxidation states.

To understand why, we have to look at their energy levels. In the actinoid series, the $5f$, $6d$, and $7s$ orbitals are remarkably close to each other in terms of energy.

Because the energy gap ($\Delta E$) between these subshells is so incredibly small, the electrons don't just stay confined to their specific orbitals when it comes to chemical bonding. Instead, electrons from all three subshells—$5f$, $6d$, and $7s$—can easily participate.

This unique property is the secret behind their ability to expand their oxidation states significantly. They can lose or share a large number of valence electrons, leading to highly oxidized compounds.

Let us focus on Uranium (U), a famous early actinoid with an atomic number of $92$. If we look at its electronic configuration, it is $[\text{Rn}]5f^{3}6d^{1}7s^2$.

Uranium has the ability to lose all six of these valence electrons. By doing so, it achieves a maximum oxidation state of $+6$. A classic, real-world example of this is Uranium hexafluoride ($U{F}_6$), a compound heavily used in the uranium enrichment process.

Moving a bit further down the series, we encounter Plutonium (Pu), with an atomic number of $94$. Its electronic configuration is $[\text{Rn}]5f^{6}7s^2$.

Plutonium pushes the boundaries even further. It can utilize up to seven of its valence electrons for bonding, reaching an impressive maximum oxidation state of $+7$! While these $+7$ compounds are rare and highly oxidizing, they do exist under specific conditions.

Bringing it all together, the highest possible oxidation states for Uranium and Plutonium are $+6$ and $+7$, respectively.

As a bonus fact, it is crucial to remember the general trend among the early actinoids. The maximum oxidation state increases from Uranium ($+6$) to Neptunium ($+7$) and Plutonium ($+7$), and then it drops back down for Americium ($+6$). This specific trend is a favorite concept for examiners, so keep it locked in your memory!