[mc1990]

Hi,

I hope I'm not on the wrong forum, but I have a question regarding the actinides and their oxidation states. The early actinides possess a wide range of oxidation states, diverging from the lanthanides, which is explained by relativistic electron effects. Namely the f- and d-orbitals are more (chemically) available for the early actinides and thus have a wide range of oxidation states. Now that's clear, but what I don't get is why the late actinides then resemble the lanthanides? The relativistic effect still holds for these elements, so why are they suddenly reduced to the dominant +3 ox. state? Is it because the 5f-orbitals lower in energy after 95Am, and, if so, why is that so? I hope someone has an answer!

Greetings,
Mitchel

[mc1990]

(*Ignore me, I am impatient*) Anyone can help me?

[MattChe32413231aeerwea]

Hey man I appreciate that this is 2 years too late, that you've probably finished your degree and don't care anymore/ have already found out. However, I shall reply for revision and incase you still care.

Although the relativistic effect does mean the 5f orbitals are further from the nucleus due to the indirect relativistic orbital expansion, there is something else we have to consider. Much like the lanthanides, the actinides have a contraction. The actinide 5f orbitals are bad at shielding, and as a result there is an actinide contraction. Therefore towards the end of the row this poor shielding overcomes the indirect relativistic effect, and means the orbitals are pulled into the nucleus as they feel the metal ion's attraction, the high charge  density. As the electrons are pulled in there is a smaller radius, the element is more ionic in it's bonding and favors lower oxidation states. As it is more ionic it behaves like the lanthanides.