synthetic elements

synthetic elements,

in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetiumtechnetium
[Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200°C;; b.p. 4,877°C;; sp. gr. 11.5 (calculated); valence +4, +6, or +7.
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 (at. no. 43), which was the first element to be synthesized, promethiumpromethium
, artificially produced radioactive chemical element; symbol Pm; at. no. 61; mass no. of most stable isotope 145; m.p. 1,042°C;; b.p. 3,000°C; (estimated); sp. gr. unknown; valence +3.
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 (at. no. 61), astatineastatine
[Gr.,=unstable], semimetallic radioactive chemical element; symbol At; at. no. 85; at. wt. of most stable isotope 210; m.p. 302°C; (estimated); b.p. 337°C; (estimated); density unknown; valence believed to be +1, +3, +5, or +7.
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 (at. no. 85), franciumfrancium
[from France], radioactive chemical element; symbol Fr; at. no. 87; mass no. of most stable isotope 223; m.p. about 27°C; (estimated); b.p. 677°C; (estimated); sp. gr. unknown; valence +1.
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 (at. no. 87), and the transuranium elementstransuranium elements,
in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ.
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 (at. no. 93 and beyond in the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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). Some of these elements have since been shown to exist in minute amounts in nature, usually as short-lived members of natural radioactive decay series (see radioactivityradioactivity,
spontaneous disintegration or decay of the nucleus of an atom by emission of particles, usually accompanied by electromagnetic radiation. The energy produced by radioactivity has important military and industrial applications.
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).

The synthetic elements through at. no. 100 (fermiumfermium
[for Enrico Fermi], artificially produced radioactive chemical element; symbol Fm; at. no. 100; mass no. of most stable isotope 257; m.p. 1,527°C;; b.p. and sp. gr. unknown; valence +2, +3. Fermium is a member of Group 3 of the periodic table.
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) are created by bombarding a heavy element, such as uranium or plutonium, with neutrons or alpha particles. The synthesis of the transfermium elements (elements with at. no. 101 or greater) is accomplished by the fusion of the nuclei of two lighter elements. Elements 101 through 106 were first produced by fusing the nuclei of slightly lighter elements, such as californiumcalifornium
[from California], artificially produced, radioactive metallic chemical element; symbol Cf; at. no. 98; mass no. of most stable isotope 251; m.p. about 900°C;; b.p. about 1,470°C;; density unknown; valence +3.
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, with those of light elements, such as carboncarbon
[Lat.,=charcoal], nonmetallic chemical element; symbol C; at. no. 6; interval in which at. wt. ranges 12.0096–12.0116; m.p. about 3,550°C;; graphite sublimes about 3,375°C;; b.p. 4,827°C;; sp. gr. 1.8–2.1 (amorphous), 1.9–2.3 (graphite), 3.
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. Elements 107 through 112 were first produced by fusing the nuclei of medium-weight elements, such as bismuthbismuth
[Ger. Weisse Masse=white mass], metallic chemical element; symbol Bi; at. no. 83; at. wt. 208.98040; m.p. 271.3°C;; b.p. about 1,560°C;; sp. gr. 9.75 at 20°C;; valence +3 or +5.
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 or leadlead,
metallic chemical element; symbol Pb [Lat. plumbum]; at. no. 82; at. wt. 207.2; m.p. 327.502°C;; b.p. about 1,740°C;; sp. gr. 11.35 at 20°C;; valence +2 or +4.
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, with those of other medium-weight elements, such as ironiron,
metallic chemical element; symbol Fe [Lat. ferrum]; at. no. 26; at. wt. 55.845; m.p. about 1,535°C;; b.p. about 2,750°C;; sp. gr. 7.87 at 20°C;; valence +2, +3, +4, or +6. Iron is biologically significant.
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, nickelnickel,
metallic chemical element; symbol Ni; at. no. 28; at. wt. 58.6934; m.p. about 1,453°C;; b.p. about 2,732°C;; sp. gr. 8.902 at 25°C;; valence 0, +1, +2, +3, or +4.
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, or zinczinc,
metallic chemical element; symbol Zn; at. no. 30; at. wt. 65.38; m.p. 419.58°C;; b.p. 907°C;; sp. gr. 7.133 at 25°C;; valence +2. Zinc is a lustrous bluish-white metal. It is found in Group 12 of the periodic table.
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. Most of the elements with at. no. 113 through at. no. 118 were discovered by bombarding plutonium, americium, or a heavier transuranium element in the actinide series with calcium; the Japanese scientists who synthesized element 113, however, fused bismuth with zinc.

The transfermium elements are produced in very small quantities (one atom at a time), and identification is therefore very difficult because of half-liveshalf-life,
measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
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 ranging from minutes to milliseconds and the need to identify the products by methods other than known chemical separations. This has led to controversy over reported discoveries and over the naming of the elements. It has been predicted that one isotope of element 114—containing 114 protons and 184 neutrons—would be very stable because its nucleus would have a full complement of protons and neutrons. Termed an "island of stability," its half-life might be measured in years. However, none of the isotopes of element 114 synthesized as yet have as many as 184 neutrons, and their half-lives are still in the millisecond range (see fleroviumflerovium,
artificially produced radioactive chemical element; symbol Fl; at. no. 114; mass number of most stable isotope 289; m.p., b.p., sp. gr., and valence unknown. Situated in Group 14 of the periodic table, it is expected to have properties similar to those of lead and tin.
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).

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