Inner transition element

The inner transition metals are two series of elements known as the lanthanides and actinides. They are usually shown below all the other elements in the standard view of the periodic table, but they really belong to periods 6 and 7. The lanthanide series consists of the 14 elements (atomic numbers 58–71) immediately following lanthanum, and the actinide series similarly consists of the 14 elements (atomic numbers 90–103) immediately following actinium. These elements were among the last to be discovered and placed in the periodic table. Many of the actinides do not occur naturally but were synthesized through nuclear reactions. Chemically, the elements within each series are very similar to each other, particularly the lanthanides. Among them, the two most well-known elements are uranium (U) and plutonium (Pu), which are used for the generation of nuclear power.

The Inner Transition Elements

Lanthanides

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

71 Lu

Actinides

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

103 Lr

Definition

The definition of inner tranisition metals is somewhat imprecise. Some include lanthanum and actinium to give 15 elements in each series. From the standpoint of their electronic structure, the lanthanides are characterized by the gradual filling of the 4f subshell, and the actinides, by the filling of the 5f subshell. Consequently, they are also called "f-block" elements.

In these elements, however, the outermost d and f subshells lie close together in energy, leading to some irregularities in electronic structure. These irregularities in turn lead to some uncertainty about where to place the elements (see the periodic table showing electron configurations). Lanthanum and actinium have no electrons in their f subshells, and they best fit with the elements of group 3. Cerium and thorium also have no f electrons but are considered part of the inner transition metal series. A commmon arrangement is to place the inner transition metals between groups 3 and 4 as shown in the inline table.

Lanthanides

Atomic No.	Name	Symbol
58	Cerium	Ce
59	Praseodymium	Pr
60	Neodymium	Nd
61	Promethium	Pm
62	Samarium	Sm
63	Europium	Eu
64	Gadolinium	Gd
65	Terbium	Tb
66	Dysprosium	Dy
67	Holmium	Ho
68	Erbium	Er
69	Thulium	Tm
70	Ytterbium	Yb
71	Lutetium	Lu

The term lanthanides indicates that the elements in this series follow lanthanum in the periodic table. The 14 elements in the lanthanide series are: cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium(Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

Together with scandium and yttrium, the lanthanides are also sometimes referred to by the trivial name "rare earths." This name is not recommended by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are neither rare in abundance (even the least abundant, lutetium, is more abundant in the Earth's crust than gold), nor are they "earths" (an obsolete term for oxides). In addition, the IUPAC currently recommends using the name lanthanoid rather than lanthanide, because the suffix "-ide" is generally used for anions.

Chemistry

The lanthanides are chemically similar to one another, and useful comparisons can also be made with scandium, yttrium, and the actinides. Except for cerium and europium, the lanthanides occur naturally in ionic compounds as ions with a 3+ charge. Going down the series, the radii of the lanthanide 3+ ions decrease—a phenomenon known as the "lanthanide contraction."

The 3+ oxidation state is a universal preference for these elements. As a consequence, their geochemical behavior is a regular function of ionic radius and, therefore, atomic number. This property results in variations in the abundances of lanthanides. It also makes them difficult to separate.

Chemically, the lanthanides react with water to liberate hydrogen. In this regard, they resemble the alkali or alkaline earth elements more than they do the transition metals. Although the 3+ oxidation state is the most important, the 2+ state is also important, especially for europium and ytterbium, and cerium forms a stable 4+ ion.

Uses

Most lanthanides are widely used in lasers. Given that they can deflect ultraviolet and infrared rays, they are commonly used in sunglass lenses. In addition, two of the lathanides (Sm and Lu) have radioactive isotopes (¹⁴⁷Sm and ¹⁷⁶Lu) with long half-lives, and they are used to date minerals and rocks from the Earth, Moon, and meteorites.

Actinides

Atomic No.	Name	Symbol
90	Thorium	Th
91	Protactinium	Pa
92	Uranium	U
93	Neptunium	Np
94	Plutonium	Pu
95	Americium	Am
96	Curium	Cm
97	Berkelium	Bk
98	Californium	Cf
99	Einsteinium	Es
100	Fermium	Fm
101	Mendelevium	Md
102	Nobelium	No
103	Lawrencium	Lr

The actinide series, in a fashion similar to the lanthanides, is named after the element actinium. The 14 elements in the actinide series are: thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr). The IUPAC currently recommends using the name actinoid rather than actinide, as the suffix "-ide" is generally used to indicate anions.

Chemistry

Phase diagram of the actinide elements.

In many ways, the chemical properties of the actinides repeat those of the lanthanides, but the similarities among the actinides are less pronounced than those among the lanthanides. There is an "actinide contraction," but it is less regular than the lanthanide contraction. In addition, the actinides exhibit a wider range of oxidation states. Initially, this led to some confusion as to whether thorium and uranium should be considered d-block elements.

Unlike the lanthanides, all the actinides are radioactive. Most have fairly short half lives and are not found naturally in the Earth's crust—only thorium and uranium occur naturally. The remaining actinides were synthesized artificially during the twentieth century, by techniques such as neutron bombardment. Members of the latter half of the series have such exceedingly short half-lives that it is not feasible to investigate their chemistry.

Some of the actinides have been produced in sufficient quantities to investigate their chemical properties, and they show interesting phase behavior (see diagram above). Plutonium, for example, can reorganize its crystal structure significantly with relatively small changes in temperature, thereby altering its density (and volume) by up to 25%.

Uses

• "Thorium, uranium, and plutonium, can be used as fuel in nuclear reactors."

• enriched uranium is used for generating electricity in nuclear power plants.

• "After the discovery in 1939 that it could undergo nuclear fission, uranium gained importance with the development of practical uses of nuclear energy. The first atomic bomb used in warfare was a uranium bomb. This bomb contained enough of the uranium-235 isotope to start a runaway chain reaction which in a fraction of a second caused a large number of the uranium atoms to undergo fission, there by releasing a fireball of energy."

• "Uranium enriched over 85% is also known as "weapons grade". In a breeder reactor, ²³⁸U can also be converted into plutonium."

• "Currently the major application of uranium in the U.S. military sector is in high-density penetrators. This ammunition consists of depleted uranium alloyed with 1–2% other elements. The applications of these armour-piercing rounds range from the 20mm Phalanx gun of the U.S. Navy for piercing attacking missiles, through the 30mm gun in A-10 aircraft, to 105mm and larger tank barrels. At a high speed of impact, the bullet's density, hardness, and flammability enable penetration into heavily armoured targets."

External links

• USGS Rare Earths Statistics and Information

Periodic tables

Standard table | Vertical table | Table with names | Names and atomic masses (large) | Names and atomic masses (small) | Names and atomic masses (text only) | Inline F-block | Elements to 218 | Electron configurations | Metals and non metals | Table by blocks | List of elements by name

Groups:   1 -  2 -  3 -  4 -  5 -  6 -  7 -  8 -  9 - 10 - 11 - 12 - 13 - 14 - 15 - 16 - 17 - 18

Periods:  1  -  2  -  3  -  4  -  5  -  6  -  7  -  8

Series:   Alkalis  -  Alkaline earths  -  Lanthanides  -  Actinides  -  Transition metals  -  Poor metals  -  Metalloids  -  Nonmetals  -  Halogens  -  Noble gases

Blocks:  s-block  -  p-block  -  d-block  -  f-block  -  g-block

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