TRANSURANIUM ELEMENTS—SEABORG PAS Ti 
have led to the production of over 100 atoms of mendelevium. The 
indications are that mendelevium is a typical tripositive actinide 
element and a true eka-thulium, as expected. 
ELEMENT 102 
The discovery of element 102 was announced in 1957 as the result of 
work done at the Nobel Institute for Physics in Stockholm by a team 
of scientists from the Argonne National Laboratory, the Atomic 
Energy Research Establishment at Harwell, and the Nobel Institute. 
An isotope of the element was reportedly produced by bombarding 
Cm? with cyclotron-produced C¥“ ions and decayed with a half- 
life of about 10 minutes by the emission of 8-5 MeV alpha particles. 
The name nobelium for element 102 was suggested by this group. 
Unfortunately it has not been possible to confirm this discovery in 
experiments performed at the University of California Radiation 
Laboratory. In April 1958 a group consisting of Ghiorso, T. Sikke- 
land, J. R. Walton, and the author at the Radiation Laboratory 
identified the isotope 10274 as a product of the bombardment of Cm?** 
with C™ ions accelerated in the new heavy-ion linear accelerator 
there. (The reaction is Cm?#*(C™, 4n)102%*). The element 102 
isotope decays by alpha-particle emission with a half-life of about 
3 seconds. It was detected by the chemical identification of its known 
daughter Fm, the atoms of the daughter element being separated 
from the parent element 102 by taking advantage of the recoil due to 
element 102 alpha-decay. Although the name nobelium for element 
102 will undoubtedly have to be changed, the investigators have not, 
at the time of writing, made their suggestion for the new name. 
COMPARISON OF ACTINIDES AND LANTHANIDES 
The resemblance between the actinide and lanthanide elements sug- 
gests that their electronic structures must besimilar. In the lanthanide 
elements, the 14 4f electrons are added one by one, beginning with 
cerium (atomic number 58) and ending with lutetium (atomic num- 
ber 71). In the actinide elements, 14 5f electrons are added, beginning 
formally with thorium and ending with element 103. The evidence 
for this, which is too complex and lengthy to discuss in this article, 
lies in the chemical properties, absorption and fluorescence spectra in 
aqueous solution and crystals, crystallographic structure data, mag- 
netic data, and spectroscopic data. The lanthanide gadolinium, with 
seven 4f electrons, and the actinide curium, with seven 5f electrons, 
are of especial interest because of the enhanced stability of the half- 
filled f-electron shell configuration. The two elements have been found 
to have properties that are strikingly similar. The family relation- 
ship within the actinide group means that the study of any one of 
