Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.


Lanthanum (Greek lanthanein, “to escape notice”), symbol La, metallic element with an atomic number of 57. Lanthanum is one of the rare earth elements of the periodic table. Lanthanum is often regarded as the first member of the lanthanide series, to which it gives its name.

Lanthanum was discovered by the Swedish chemist Carl Gustav Mosander in 1839. It burns in air at about 450° C (about 842° F) to form lanthanum oxide, La2O3. It forms colorless trivalent salts, including one of the strongest trivalent bases, which is used by analytical chemists. It generally occurs with other rare earth elements in such minerals as apatite and monazite and in certain kinds of calcite and fluorspar. It is fairly common, ranking 28th in order of abundance of the elements in the earth's crust. Impure lanthanum is used in alloys such as misch metal, of which lanthanum is a major constituent. Cigarette-lighter flints are made from this alloy. Lanthanum oxide is used in certain types of optical glass.

Lanthanum melts at about 918° C (about 1684° F), boils at about 3464° C (about 6267° F), and has a specific gravity of 6.15. The atomic weight of lanthanum is 138.91.