Oxidation States

The actinoids display a noticeably wider spread of oxidation states than the lanthanoids do. This is partly explained by the electronic structure of the series: the $5f$, $6d$, and $7s$ levels lie close enough in energy to each other that electrons from more than one of these subshells can be involved in bonding, opening up a larger set of accessible oxidation states (the full range for each element is collected in the accompanying oxidation-states table).

The +3 state is the general, characteristic oxidation state across the series, just as it is for the lanthanoids. But the elements in the first half of the actinoid series show a distinct tendency to reach much higher oxidation states as well. The maximum oxidation state climbs steadily through the early actinoids — from $+4$ in thorium, up to $+5$, $+6$, and $+7$ in protactinium, uranium, and neptunium respectively — before falling away again in the elements that follow neptunium. …