PTL:Curium

From ChemEd Collaborative

Curium is a member of the actinide series, which stretches from actinium (Ac) to lawrencium (Lr). Curium is a synthetic element; none occurs naturally on earth.

1 Discovered
2 Name
3 Characteristics
4 Uses
5 Emission Spectra

Discovered

Once neptunium and plutonium had been prepared, it become evident to Seaborg and his coworkers at the University of California that it should be possible to extend the periodic table further. Ever heavier elements could be built by bombarding lighter ones with small particles such as alpha particles. Therefore, Seaborg and his group fired a beam of alpha particles at a plutonium target.

²³⁹Pu + 4 He ²⁴²Cm + 1n

Element 96, now called curium, was found early in 1944 in the first real test of these ideas. Later in the year, yet another element, number 95, was found by neutron bombardment of plutonium.

²³⁹Pu + 1n ²⁴⁰Pu

²⁴⁰Pu + 1n ²⁴¹Pu

²⁴¹Pu ²⁴¹Am + β

This other new element is now called americium. However, it took almost a year before the two elements could be chemically separated and their identity confirmed. This difficulty led one person working in that laboratory to name the new elements "pandemonium" and "delirium".

Name

The name was also chosen to parallel the name of the corresponding lanthanide element, Gd, which is immediately above curium in the periodic table. Gadolinium was named for Johan Gadolin, a well known investigator of lanthanide chemistry. Therefore, element 96 was named in honor of people who were pioneers in the discovery and chemistry of the radioactive elements, Pierre and Marie Curie.

Characteristics

The metal is silvery and almost as malleable as plutonium, but it is much more reactive than either plutonium or americium.

Chemical studies of Cm are difficult because the element is so intensely radioactive that its salts decompose water. Nonetheless, many compounds have been prepared, such as white Cm₂O₃ and black CmO₂. White or yellow halides of the type CmX₃ (X = F, Cl, and Br) are also known, as are black chlorides, bromides, and iodides of Cm(II).

Curium metal has been isolated by barium reduction of CmF₃.

3 Ba + 2 CmF₃ 3 BaF₂ + 2 Cm

Uses

Curium is used as a source of neutrons for neutron activation analysis

Like americium and californium, Cm has been used as a neutron source for [neutron activation analysis], which can detect trace quantities of many elements.

At least 14 isotopes of curium are known, ranging from mass numbers of 238 to 251. The most stable isotope is ²⁴⁷Cm, which has a half-life of about 15,600,000 years.