Elements 104-112
Prior to the atomic age, scientists believed uranium was the heaviest element with an atomic number of 92. However, this was shown to be wrong because a number of transuranium elements have been produced. Today, researchers have created elements at each position on the periodic table through element 112. No one knows exactly how many more elements exist, but current theory holds that there is a maximum of 200 possible.
Heavy elements are produced by a variety of techniques. One method that is often used is to bombard a lower transuranium element, such as plutonium, americium, or curium, with alpha particles or ions of light elements. The following is a typical example:
Element 104 is of interest to chemists because it is the first transactinideelement, that is, the first element to begin a new rare-earth-type row in the periodic table. It occupies the space below hafnium in the table.
In 1964, researchers at the Joint Nuclear Research Institute at Dubna, in the former Soviet Union, reported that they had produced an isotope of element 104 by bombarding plutonium-242 with neon-22 nuclei. They proposed the name kurchatovium (Ku) for the element, in honor of Soviet nuclear physicist, Igor Kurchatov (1903-1960).
Five years later, a group of scientists at the University of California at Berkeley also reported the production of element 104 by the reaction shown in the equation above. They suggested the name rutherfordium (Rf), in honor of Ernest Rutherford.
During the late 1960s and early 1970s, the Dubna and Berkeley groups also reported the discovery of elements 105 and 106. Names proposed for element 105 are hahnium (Ha), nielsbohrium, and bohrium.
The Dubna team announced the discovery of element 107 in 1976. They produced unnilseptium-261 by bombarding bismuth -204 nuclei with chromium-54 nuclei. This discovery was confirmed by scientists at the Heavy Ion Research Laboratory at Darmstadt, Germany, in 1982. The German team was able to produce and study six atoms of the new element.
The Darmstadt team also succeeded in making a single nucleus of element 109 in 1982. They followed the nucleus through a series of nuclear changes that matched those predicted for the element. Later in that decade, they produced element 108. In 1994, they announced the discovery of elements 110 and 111. In 1998, the produced the first known sample of element 112 by smashing lead atoms into zinc atoms in a linear accelerator. Since lead has 82 protons and zinc has 30, some of the atoms briefly stuck together as element 112.
The very short half-lives and small quantities of transactinide isotopes produced so far make the study of their physical and chemical properties very difficult. It is believed that these elements will behave similar to elements above them in the periodic table. For example, element 104 is expected to behave like hafnium. Similarly, element 105 would have chemical properties like tantalum, and 106 would be like tungsten.
The problem of naming the transactinide elements has been addressed by the International Union of Pure and Applied Chemistry (IUPAC). Traditionally, the person or group responsible for discovering a new element was given the right to name it. After an element's existence is independently verified, their proposed name is then ratified and adopted by IUPAC. In the case of these transactinide elements, the verification of newly created elements is difficult. Therefore, it is sometimes hard to determine who discovered an element first. This created a controversy and it was only in 1998 that names for elements 101 to 109 were ratified. These include Mendelevium (Md) for element 101, Nobelium (No) for element 102, Lawrencium (Lr) for element 103, Rutherfordium (Rf) for element 104, Dubnium (Db) for element 105, Seaborgium (Sg) for element 106, Bohrium (Bh) for element 107, Hassium (Hs) for element 108 and Meitnerium (Mt) for element 109. Names for elements 110, 111, and 112 are now under review.
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