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Lawrencium

physical science Maturity 11-13 Next article →

Lawrencium is a synthetic chemical element with the symbol Lr and atomic number 103. Because it is synthetic, it does not occur naturally in the environment. It is a radioactive metal and serves as the eleventh transuranium element. It is also the third transfermium element. Most importantly, lawrencium is the very last member of the actinide series.

F-block elution sequence
F-block elution sequence

Creating lawrencium requires high-energy physics. Since it is a heavy element, it can only be produced in particle accelerators. Scientists create it by bombarding lighter elements with charged particles. This process forces nuclei together to form a new, heavier atom. There are fourteen known isotopes of lawrencium. The most stable isotope is 266Lr, which has a half-life of 11 hours. However, scientists often use 260Lr for chemistry experiments. Even though 260Lr has a short half-life of only 2.7 minutes, it can be produced on a larger scale.

Chemists study lawrencium to see how it fits into the periodic table. Experiments show that lawrencium behaves as a heavier homolog to lutetium. This means it shares many chemical properties with lutetium. Lawrencium is trivalent, which means its ions typically have a charge of +3. Because of this, some scientists classify it as the first of the 7th-period transition metals. Its electron configuration is actually anomalous for its position. Instead of the s2d configuration seen in lutetium, lawrencium has an s2p configuration. Interestingly, this unusual arrangement does not seem to change its chemical behavior.

The discovery of lawrencium was a long and disputed process. During the 1950s, 1960s, and 1970s, many laboratories made claims about synthesizing element 103. These claims came from scientists in both the United States and the Soviet Union. The priority of the discovery led to a disagreement over the element's name.

96904536.thumb3
96904536.thumb3

Initially, the International Union of Pure and Applied Chemistry (IUPAC) gave credit to the American team. In 1992, the IUPAC reevaluated the evidence. They decided to give shared credit to both the Soviet and American teams. They did not change the name, which remained lawrencium.

Significant breakthroughs occurred at the Lawrence Berkeley National Laboratory. On February 14, 1961, a team led by Albert Ghiorso performed a major experiment.

They bombarded a three-milligram target of californium isotopes with boron-10 and boron-11 nuclei. They used the Heavy Ion Linear Accelerator, or HILAC, for this work. They originally reported finding the isotope 257Lr. They later corrected this to 258Lr after further testing. While the initial evidence was not fully convincing to everyone, it was a vital step toward the confirmed discovery.

In the Soviet Union, scientists at the Joint Institute for Nuclear Research in Dubna also conducted important work. They reported making 256Lr in 1965 by bombarding americium-243 with oxygen-18.

Ernest Lawrence
Ernest Lawrence

They identified the element indirectly by looking at its granddaughter, fermium-252. Later, in 1971, the Berkeley team successfully measured the decay properties of isotopes from mass 255 to 260. This work confirmed the previous results from both Berkeley and Dubna. Finally, in 1976 and 1977, scientists measured X-ray energies from 258Lr. These measurements dispelled all remaining doubts about the discovery.

Lawrencium is named after Ernest Lawrence. He was the inventor of the cyclotron, a device used to discover many artificial radioactive elements.

Ernest Lawrence
Ernest Lawrence

Physically, lawrencium is expected to be a silvery, heavy metal. It is predicted to have a density of about 14.4 g/cm3. It is also expected to be a solid with a hexagonal close-packed crystal structure. This structure is similar to the lighter element lutetium. Scientists estimate its melting point is around 1900 K, which is 1600 degrees Celsius. These properties help scientists understand how heavy elements behave at the edge of the periodic table.

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