The Lanthanide Series

Lanthanum, is extensively used for carbon-arc electrodes. It was discovered in 1839 by Carl Mosander.

Symbol: La. Atomic number: 57. Atomic weight: 138.9055. Melting point: 1,688 F. (920 C). Boiling point: 6,249 F. (3,454 C). Specific gravity: 6.15. Valence: 3.

Cerium, is the most abundant of the rare earths. Cerium is used as a component of glass and as an abrasive in polishing glass surfaces. Cerium compounds serve as catalysts in the refining of petroleum. The element was discovered in 1803 by J. J. Berzelius and W. Hisinger working together, and also by M. H. Klaproth.

Symbol: Ce. Atomic number: 58. Atomic weight: 140.12. Melting point: 1,468 F. (798 C). Boiling point: 6,199 F. (3,426 C). Specific gravity: 6.66. Valence: 3 or 4.

Praseodymium, was first separated from didymium (a mixture of rare-earth elements consisting chiefly of praseodymium and neodymium) in 1885 by Baron Carl Auer von Welsbach. The existence of didymium was first reported in 1841 by Carl Mosander, who believed it to be a single element. Praseodymium is used to color glass and glazes. Glass colored with didymium is used in welder's goggles.

Symbol: Pr. Atomic number: 59. Atomic weight: 140.9077. Melting point: 1,708 F. (931 C). Boiling point: 6,354 F. (3,512 C). Specific gravity: 6.77. Valence: 3 or 4.

Neodymium, is used for the same purposes as praseodymium. It was first separated from didymium in 1885 by Baron Carl Auer von Welsbach.

Symbol: Nd. Atomic number: 60. Atomic weight: 144.24. Melting point: 1,850 F. (1,010 C). Boiling point: 5,554 F. (3,068 C). Specific gravity: 7.0. Valence: 3.

Promethium, is produced only in nuclear reactors. It was identified in 1945 by J. A. Marinsky and L. E. Glendenin, at Oak Ridge, Tennessee.

Symbol: Pm. Atomic number: 61. Atomic weight of the most stable known isotope: approximately 145. Melting point: about 1,976 F. (1,080 C). Boiling point: 4,460 F. (2,460 C). Specific gravity: 7.22. Valence: 3.

Samarium, was discovered in 1879 by Lecoq de Boisbaudran. It is used in infrared-absorbing glass, as an absorber of neutrons in nuclear reactors, and as an additive to crystals for lasers.

Symbol: Sm. Atomic number: 62. Atomic weight: 150.36. Melting point: 1,962 F. (1,072 C). Boiling point: 3,232 F. (1,778 C). Specific gravity: 7.54. Valence: 2 or 3.

Europium, the most chemically reactive of the rare earths, was discovered and prepared as an oxide in 1896 by Eugene Demarcay, who isolated it in relatively pure form in 1901. Europium oxide is used with yttrium to form the red phosphors of color-television tubes.

Symbol: Eu. Atomic number: 63. Atomic weight: 151.96. Melting point: 1,512 F. (822 C). Boiling point: 2,907 F. (1,597 C). Specific gravity: 5.25. Valence: 2 or 3.

Gadolinium, was discovered in 1880 by Jean Charles Galissard de Marignac. It is used in metallic alloys to improve resistance to heat and oxidation.

Symbol: Gd. Atomic number: 64. Atomic weight: 157.25. Melting point: 2,392 F. (1,311 C.). Boiling point: about 5,851 F. (3,233 C). Specific gravity: 7.90. Valence: 3.

Terbium, was discovered in 1843 by Carl Mosander. It is added to chemicals used in solid-state devices. Sodium terbium borate is used in laser crystals.

Symbol: Tb. Atomic number: 65. Atomic weight: 158.9254. Melting point: 2,480 F. (1,360 C). Boiling point: 5,653 F. (3,123 C). Specific gravity: 8.23. Valence: 3 or 4.

Dysprosium, was discovered in 1886 by Lecoq de Boisbaudran. It is used in nuclear reactors to absorb neutrons.

Symbol: Dy. Atomic number: 66. Atomic weight: 162.50. Melting point: 2,564.6 F. (1,407 C). Boiling point: 4,712 F. (2,600 C). Specific gravity: 8.55. Valence: 3.

Holmium, was discovered in 1878 by J. L. Soret and M. Delafontain and, independently, by P. T. Cleve in 1879.

Symbol: Ho. Atomic number: 67. Atomic weight: 164.9304. Melting point: 2,678 F. (1,470 C). Boiling point: 4,928 F. (2,720 C). Specific gravity: 8.78. Valence: 3.

Erbium, was discovered in 1843 by Carl Mosander. When added to metals, it improves their workability. Erbium oxide is used to give glass and glazes a pink color.

Symbol: Er. Atomic number: 68. Atomic weight: 167.26. Melting point: 2,772 F. (1,522 C). Boiling point: 5,185 F. (2,863 C). Specific gravity: 9.05. Valence: 3.

Thulium, was discovered in 1879 by P. T. Cleve.

Symbol: Tm. Atomic number: 69. Atomic weight: 168.9342. Melting point: 2,813 F. (1,545 C). Boiling point: 3,537 F. (1,947 C). Specific gravity: 9.31. Valence: 2 or 3.

Ytterbium, was discovered in 1878 by J. Marignac. However, it was not isolated and distinguished from another new element—lutetium—until 1907, by G. Ur-bain and Baron Carl Auer von Welsbach (independently).

Symbol: Yb. Atomic number: 70. Atomic weight: 173.04. Melting point: 1,515 F. (824 C). Boiling point: 2,179 F. (1,193 C). Specific gravity: 6.97. Valence: 2 or 3.

Lutetium, was discovered in 1907 by G. Urbain, and, independently, by Baron Carl Auer von Welsbach.

Symbol: Lu. Atomic number: 71. Atomic weight: 174.967. Melting point: 3,013 F. (1,656 C). Boiling point: 5,999 F. (3,315 C). Specific gravity: 9.84. Valence: 3.