Occasionally the names are confused and 15 elements including lanthanum may be called lanthanides. Because the three stages of ionization enthalpy of lanthanoid elements are comparative low, they are positive elements and readily assume trivalent ionic states. See more Encyclopedia articles on: Compounds and Elements.
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Cite this Article Format. Helmenstine, Anne Marie, Ph. Some of them can be cut with a knife. The hardness of thorium is similar to that of soft steel, so heated pure thorium can be rolled in sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium but is harder than both of them.
Unlike the lanthanides, most elements of the actinide series have the same properties as the d block. Members of the actinide series can lose multiple electrons to form a variety of different ions.
All actinides are radioactive, paramagnetic, and, with the exception of actinium, have several crystalline phases. All actinides are pyrophoric, especially when finely divided i. The melting point of actinides does not have a clear dependence on the number of f electrons. Like the lanthanides, all actinides are highly reactive with halogens and chalcogens; however, the actinides react more easily. Actinides, especially those with a small number of 5f electrons, are prone to hybridization.
This is explained by the similarity of the electron energies at the 5f, 7s, and 6d subshells.
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