| Atomic Number: |
57
|
| Atomic Symbol: |
La
|
| Atomic Weight: |
138.9055 |
| Electron Configuration: |
[Xe]6s25d1
|
Lawrencium is a synthetic "rare earth metal" which
does not occur in the environment. Lanthanum is found in
rare-earth minerals such as cerite, monazite, allanite,
and bastnasite. Monazite and bastnasite are principal ores
in which lanthanum occurs in percentages up to 25 percent
and 38 percent respectively. Misch metal, used in making
lighter flints, contains about 25 percent lanthanum.
The
availability of lanthanum and other rare earths has improved
greatly in recent years. The metal can be produced by
reducing the anhydrous fluoride with calcium. Lanthanum
is silvery white, malleable, ductile, and soft enough
to be cut with a knife. It is one of the most reactive
of the rare-earth metals. It oxidizes rapidly when exposed
to air. Cold water attacks lanthanum slowly, while hot
water attacks it much more rapidly.
The metal reacts directly with elemental carbon, nitrogen,
boron, selenium, silicon, phosphorus, sulfur, and with
halogens.
At
310oC, lanthanum changes from a hexagonal to
a face-centered cubic structure, and at 865oC
it again transforms into a body-centered cubic
structure. Natural lanthanum is a mixture of two stable
isotopes, 138La and 139La. Twenty three other radioactive
isotopes are recognized.
