The Physics
Factbook
An encyclopedia of scientific essays

Mass of the Heaviest Man-Made Element

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Beurstein, Bruce. Chemistry. New Jersey: Prentice Hall, 1997: inside back cover. "Lr 103 (260)" 260 amu
The World Book. New Jersey: Prentice Hall, 1996: 123. "By bombarding a lead target with zinc atoms they produced an atom of the element that had the atomic weight of 277 amu" 277 amu
Krebs, Robert. The History and Use of our Earth Elements. New Jersey: Greenwood Press, 1998: 280. "atomic weight: 277 amu" 277 amu
Neft, Zizte. Chemistry. New York: Glencoe, 1977: inside front cover. "103 Lr 257 amu" 257 amu
Element 112 Discovered at GSI. Gesellschaft für Schwerionenforschung (GSI). "The identified isotope is now the heaviest atom ever produced by man and has an atomic mass of 277" 277 amu
New Element. Russell For President 2000. Bill Neely from the science dept. of campaign headquarters and parts unknown. "The heaviest element known to science has been discovered … named Administratium (Ad) … atomic mass of 312" 312 amu
(a joke)

An element is a substance that cannot be decomposed into other substances by means of a chemical change. It is consists entirely of atoms with the same atomic numbers.

The concept of an element as it is understood today did not develop until the 17th century. By 1860, more than 60 elements were known. Scientific progress in the past and present have led to discoveries of more and more elements; some are made in nature; some are man-made; some exist only in theory; and some are yet to be named. These last few decades brought to light heavy elements, adding more to our periodic table. Currently, there are over 120 known elements.

I have investigated different sources to determine the mass of the heavies man-made element. My textbook search has yielded Lawrencium (Lr), with 260 amu (atomic mass unit). My reference work and book searches have yielded Ununbium (Uub) with 277 amu. The contradiction among the sources can be attributed to the time that these works were published. Some sources are older than others and since then newer and heavier elements have been discovered. I have determined the mass of Ununbium, which is element 112, as the mass of the heaviest element since it is the most recent. Interestingly, I surfed over the Internet and found that Administratium (Ad) is the heaviest element, with 312 amu. But I later found out this is a joke; it is reported to have 1 neutron, 125 deputy neutron, 75 associate neutrons, 111 deputy associate neutrons, and a atomic number of 0.

Kim Fai Wong -- 1998

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Schewe, Phillip F. & Stein, Ben. Element 114. Physics News. (27 January 1999). "atoms of element 114 (with a nuclear weight of 289) were detected" 289 amu
Ninov, V. et al. Observation of Superheavy Nuclei Produced in the Reaction of 86Kr with 208Pb. Physical Review Letters. 83, 6 (9 August 1999): 1104-1107. "The observed chains are consistent with the formation of 293118 and its decay by sequential alpha -particle emission to 289116, 285114, 281112, 277110, 273Hs (Z = 108) and 269Sg (Z = 106)." 293 amu
Two New Elements. Physical Review Focus. 6 August 1999. "A team at the Lawrence Berkeley National Laboratory (LBNL) in California has created elements 116 and 118, which extends the chart into a region long-predicted to contain extra-stable nuclei." -
"Berkeley Lab Leapfrogs to Elements 116 and 118." Physics Today. (August 1999): 17-19. "After fusion, some compound nuclei emit a single neutron to become ions of the isotope 293118" 293 amu

Three new superheavy elements were produced in 1999: 114, 116, and 118.

Editor's Supplement -- 1999

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Ninov, V. et al. Editorial Note: Observation of Superheavy Nuclei Produced in the Reaction of 86Kr with 208Pb. Physical Review Letters. Vol. 89, No. 3 (1 July 2002): 039901. [a retraction of the earlier claim] -
Oganessian, Yu. Ts. et al. Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm+48Ca fusion reactions. Physical Review C. Vol. 74 (9 October 2006): 044602. "We performed the element 118 experiment at two projectile energies, corresponding to 297118 compound nucleus excitation energies of E* = 29.2±2.5 and 34.4±2.3 MeV." 297 amu

Oops! Elements 116 and 118 was not produced in 1999 at Lawrence Berkeley National Laboratory in California. They were produced in 2002 at the Joint Institute for Nuclear Research in Russia.

Editor's Supplement -- 2007