See actinium and protactinium.
Hydrogen is absorbed at high temperatures by many transition metals (scandium, 21, through copper, 29; yttrium, 39, through silver, 47; hafnium, 72, through gold, 79); and metals of the actinoid (actinium, 89, through lawrencium, 103) and lanthanoid series (lanthanum, 57, through lutetium, 71) to form hard, alloy-like hydrides.
Actinium was discovered (1899) by French chemist André-Louis Debierne in pitchblende residues left after French physicists Pierre and Marie Curie had extracted radium from them, and it was also discovered (1902) independently by German chemist Friedrich Oskar Giesel.
Actinium, the ions of which in solution are colourless, exhibits an oxidation state of +3, closely resembling the rare-earth lanthanoid elements in its chemical properties.
Element 121 should be similar in its chemical properties to lanthanum and actinium, but detailed properties have not been predicted.
The periodic table of the elements contains all of the chemical elements that have been discovered or made; they are arranged, in the order of their atomic numbers, in seven horizontal periods, with the lanthanoids (lanthanum, 57, to lutetium, 71) and the actinoids (actinium, 89, to lawrencium, 103) indicated separately below (unless otherwise stated, Figure 1 will be used as reference).
Each has 86 electrons arranged as in the atoms of the noble gas radon (which precedes actinium by three columns in the table), with three more electrons that may be positioned in the 6d and 7s orbitals (the seventh shell is outermost), and with additional electrons packing into inside orbitals.
Complexes of actinium-225 have been studied for their use in nuclear medicine.
This isotope decays to actinium-227 with a half-life of 32,760 years.
Actinium-227, which is one of the decay products of uranium-235, has a 21.8-year half-life and in turn decays almost entirely to thorium-227, but about 1 percent decays to francium-223.
Actinium-225 has a 10-day half-life, decaying by the emission of alpha particles.
