350 | The History and Use of Our Earth’s Chemical Elements The two scientists then traced the very short decay sequence of the three Une-266 atoms as

350 | The History and Use of Our Earth’s Chemical Elements The two scientists then traced the very short decay sequence of the three Une-266 atoms as

they decayed into element 107 (unnilseptium or bohrium) and element number 105 (unnil- pentium or dubnium). The decay sequence is as follows:

109 Une-266 → 107 Uns-262 + 0 n-1 (high-energy helium nucleus). Unnilseptium-262 further decays as follows:

109 Uns-262 → 105 Unp-268 + 0 n-1.

Unnilpentium-268 further decays as follows:

105 Unp-268 + -1 e-0 (high-energy electron) → 104 Unq-259 (rutherfordium). Common฀Uses None, except for research purposes. Examples฀of฀Compounds There are too few atoms of meitnerium produced at any one time to form compounds. Hazards None, except for radiation, which is not much of a risk given that only a few atoms exist

in nuclear laboratories. DARMSTADTIUM฀(UNUNNILIUM)

SYMBOL:฀Ds฀(Uun)฀ PERIOD:฀7฀ SERIES฀NAME:฀Transactinide฀ ATOMIC฀NO:฀110 ATOMIC฀MASS:฀˜281฀amu฀ VALENCE:฀Unknown฀ OXIDATION฀STATE:฀Unknown฀ NATU-

RAL฀STATE:฀Solid฀(metal) ORIGIN฀OF฀NAME:฀Named฀for฀the฀German฀city฀of฀Darmstadt. ISOTOPES:฀There฀are฀a฀total฀of฀nine฀isotopes฀of฀Uun฀(Ds),฀ranging฀from฀Uun-267฀to฀Uun-

281,฀with฀half-lives฀ranging฀from฀0.17฀milliseconds฀to฀1.1฀minute.

ELECTRON฀CONFIGURATION ฀ Energy฀Levels/Shells/Electrons฀ Orbitals/Electrons

s2,฀p6

฀ 3-M฀=฀18฀

s2,฀p6,฀d10

฀ 4-N฀=฀32฀

s2,฀p6,฀d10,฀f14

฀ 5-O฀=฀32฀

s2,฀p6,฀d10,฀f14

฀ 6-฀P฀=฀16฀

s2,฀p6,฀d8

฀ 7-Q฀=฀2฀

s2

351 Properties฀and฀Characteristics

Guide to the Elements |

The production and confirmation of elements 110 and higher required the development of new equipment. In 1994 Peter Armbruster’s team used the Heavy Ion Research Laboratory’s linear accelerator (SHIP) located in Darmstadt, Germany, to create a few atoms of element 110 that had an atomic mass of 267. The researchers bombarded a thin sheet of lead with

high-energy ions of nickel. They “fired” over one billion (1×10 18 ) nickel ions at the lead target for seven days, resulting in the fusion of just one or two atoms of ununnilium 110. Uun’s isotope, now known as darmstadtium-269, has a half-life of about 0.00017 seconds as it spontaneously decays into hassium-277 and four alpha particles in the process. Both the single atoms produced and their short half-lives have made it difficult to identify the element Uun and impossible to perform any chemistry or confirm the predicted chemical and physical properties and characteristics of element 110.

History Germany, Russia, and the United States were all involved in the synthetic production of

element 110 and those elements of higher atomic numbers. This search has been an ongoing international effort by Peter Armbruster’s team that in 1994 claimed to have discovered ele- ment 110 in their laboratory. (See “Properties and Characteristics” section for more on this discovery.)

Several years before Armbruster’s discovery, in 1991, Albert Ghiorso and others of the Berkeley group produced atoms of element 110. They did this by identifying the atoms of Uun by the products of the decay chain, using their new gas-filled Small Angle Separator System (SASSY-2). The reaction follows:

Bi-209 + Co-59 + neutron = 110 Uun-267 + alpha particle. In 1994 and 1995 Dr. Darleane Hoffman of LLNL in California and others from

Germany used the Separator for Heavy Ion Reaction Products (SHIP) at the GSI laboratory in Darmstadt, Germany, to produce two new isotopes of element 110.

Pb-208 + Ni-62 + neutrons = 110 Uun-269 + alpha particles, and Pu-208 + Ni-64 = neutrons = 110 Uun-271 + alpha particles.

Only a few atoms were produced by these processes.

A combined team of scientists from the Lawrence-Livermore National Laboratory (LLNL) in California, and from the laboratory in Dubna, Russia, reported the following “hot” fusion reaction:

Pu-244 + S-34 + neutrons = 110 Uun-273 + alpha particles. The Heavy Ion Reaction Separator (SHIP) located in the GSI laboratory in Germany was

used to identify elements 107 (bohrium) through element 109 (meitnerium) during the years 1981 through 1984, and it was used again later, between 1994 and 1996, to verify elements 110 (Uun) through element 112 (Uub).

Common฀Uses None are known except as an interest in nuclear laboratories.