336 | The History and Use of Our Earth’s Chemical Elements Properties

336 | The History and Use of Our Earth’s Chemical Elements Properties

The nuclear chemists at the Lawrence Berkeley Laboratory worked with extremely small samples of lawrencium with short half-lives, which made it difficult to determine the new element’s chemical and physical properties. Most of its isotopes spontaneously fission as they give off alpha particles (helium nuclei). Lawrencium’s melting point is about 1,627°C, but its boiling point and density are unknown.

Characteristics Lawrencium is the last of the transuranic elements and the 15th in the actinide series (there

are 15 elements in the lanthanide series as well, assuming you start counting the series at the elements lanthanide and actinium, respectively.) It is assumed that lawrencium has some chemical and physical characteristics similar to lutetium, located just above it in the lantha- nide series. It is also located at the bottom of the group 17 (VIIA) elements, which makes it the heaviest of the halides.

Abundance฀and฀Source Because lawrencium does not exist in nature, it had to be produced artificially. This was

done in 1961 by the team of scientists at Berkeley, using an ion accelerator to bombard three different isotopes of the element californium with heavy ions of the elements 10 boron and

11 boron along with some neutrons that produced the isotope 103 Lr-258. The resulting product weighed only about two millionths of a gram and had a half-life of only 4.1 seconds, fission- ing spontaneously.

History Albert Ghiorso’s team at the Lawrence Berkeley Laboratory included Torbjorn Sikkeland,

Almon E. Larsh, and Robert M. Latimer. They artificially manufactured lawrencium in 1961. They placed an incredibly small amount of californium as the target in a new instrument called

a “linear accelerator,” which speeds up particles by electromagnetic propulsion in a long straight tube to hit a target element instead of having the particles following a circular path of the cyclo- tron. Californium was the target that was bombarded in a series of steps with both 10 boron and

98 Cf- 249 + 98 Cf-252 + 10 B and 11 B + several neutrons → 103 La-257 and 103 La-258 + alpha radiation. Later in 1965, Russian scientists, using an ion accelerator, produced the isotope lawren- cium-256 by bombarding americium-243 with oxygen-18 ions.

11 boron to produce a microgram of the isotope of lawrencium-258. The reaction follows:

(Note: the original symbol for lawrencium was Lw, but it was changed by the IUPAC naming committee to Lr.)

Common฀Uses There are no common uses. So little of it exists that it has no use outside of basic scientific

research. Examples฀of฀Compounds

A few atoms of lawrencium oxide (Lr 3 O 2 ) have been produced for study, but it has no practical utility.

337 Hazards

Guide to the Elements |

Like the other short-lived radioactive isotopes, lawrencium is a radiation hazard. Also, as with the others, the danger to individuals and the public is small since there is not much of it in existence. Also, the small amount that has been produced has a short half-life, so over short periods of time it ceases to exist.

Transactinide Series: Period 7 (Continuation of Actinide Series)