In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence.They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties.
He also isolated the first sample of uranium metal by heating uranium tetrachloride with metallic potassium.
Jöns Jacob Berzelius characterized this material in more detail by in 1828.
The prevailing view that dominated early research into transuranics was that they were regular elements in the 7th period, with thorium, protactinium and uranium corresponding to 6th-period hafnium, tantalum and tungsten, respectively.
Synthesis of transuranics gradually undermined this point of view.
Compared to the lanthanides, which (except for promethium) are found in nature in appreciable quantities, most actinides are rare.
The majority of them do not even occur in nature, and of those that do, only thorium and uranium do so in more than trace quantities.While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium, protactinium, and uranium are much more similar to transition metals in their chemistry, with neptunium and plutonium occupying an intermediate position.All actinides are radioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth.The actinide series derives its name from the first element in the series, actinium.The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.The most abundant or easily synthesized actinides are uranium and thorium, followed by plutonium, americium, actinium, protactinium, neptunium, and curium.