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, cerium through lutetium (atomic numbers 58–71) immediately following lanthanum. Likewise, the actinide series consists of the 14 elements, thorium through lawrencium (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 (especially the lanthanides) are very similar to one another. Many lanthanides are used for producing lasers, sunglass lenses, and strong magnets. Some radioactive isotopes of inner transition metals are used to date rocks, minerals, and fossils. The two most well-known actinides are uranium (U) and plutonium (Pu), which are used in nuclear weapons and nuclear power plants that generate electricity.
| 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 |
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| 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 |
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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[1] 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. A number of lanthanides—such as cerium, neodymium, and samarium—can be alloyed with other metals to make strong permanent magnets. 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
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 were synthesized artificially during the twentieth century, by techniques such as neutron bombardment. Only thorium and uranium occur in significant amounts in nature, and trace amounts of plutonium have been found in uranium ores. Members of the latter half of the actinide 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 study 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
Certain isotopes of uranium and plutonium are used as fuel in nuclear weapons and nuclear reactors, and some nulcear reactor designs involve the use of thorium. Currently, the U.S. military uses uranium in high-density penetrators that can pierce heavily armored targets. In addition, thorium is used to coat tungsten wiring in electronic equipment, and a technique known as "uranium-thorium dating" is used to determine the age of carbonate materials and fossils. One type of smoke detector contains a minute quantity of americium, which produces ionizing radiation.
Reference
- ↑ Chang, Raymond, Chemistry (9th ed.), New York: McGraw Hill, 2007.
External links
| 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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