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 immediately following lanthanum, and the actinide series similarly consists of the 14 elements 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.
| 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. However, cerium and thorium also have no f electrons but are considered part of the inner transition metal series. A commmon arrangement is to place these elements between groups 3 and 4[1] as shown in the inline table.
Lanthanides
The lanthanides are named after the element lanthanum and, together with scandium and yttrium, are also sometimes referred to by the trivial name "rare earths." This name is not recommended by IUPAC, as they 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). Note that the International Union of Pure and Applied Chemistry (IUPAC) are currently recommending the name lanthanoid rather than lanthanide, as the suffix "-ide" generally indicates anions. They are characterized by electrons in the 4f subshell.
Chemistry
The lanthanides are chemically similar to each other and useful comparison can also be made with the actinides, scandium, and yttrium. The ionic radii of the lanthanide 3+ ions decrease through the period — the so-called lanthanide contraction. Except for cerium and europium the lanthanides occur naturally in ionic compounds as ions with a 3+ charge. This oxidation state is a universal preference for these elements. As a consequence, their geochemical behaviors are a regular function of ionic radius and, therefore, atomic number. This property results in variations in the abundances of lanthanides that are used to trace natural materials through physical and chemical processes. It also makes them difficult to separate. In addition, two of the lathanides have radioactive isotopes with long half-lives (147Sm and 176Lu) that are used to date minerals and rocks from Earth, the Moon and meteorites. Lanthanides are also widely used in lasers.
Chemically the lanthanides more resemble the alkali or alkaline earth elements than the transition metals in that they react with water to liberate hydrogen. Although the 3+ oxidation state is the most important the 2+ state is also important, especially for Europium (Eu) and Ytterbium (Yb), and Cerium (Ce) forms a stable 4+ ion.
Mnemonics
To remember the sequence of the lanthanide elements, various mnemonic phrases have been used. This is the most common one:
Ladies Can't Put Nickels Properly into Slot-machines. Every Girl Tries Daily, However, Every Time You Look.
In this phrase, each word's initial letter corresponds to a lanthanide element, from Lanthanum to Lutetium.
External links
Actinides
The actinide series, in a similar fashion to the lanthanides is named after the element actinium. Note that the International Union of Pure and Applied Chemistry (IUPAC) are currently recommending 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 the lanthanides, but actinides display less similarity in their chemical properties than the lanthanide series. There is an actinide contraction, but it is less regular than the lanthanide contraction and they 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 and enriched uranium is used for generating electricity in nuclear power plants. The remaining actinides were synthesized in the 20th century by techniques such as neutron bombardment. The latter half of the series possess such exceedingly short half-lives that investigating their chemistry is not feasable.
Some of these elements have been made in sufficient quantities to generate bulk samples of the metal, particularly plutonium (Pu), and investigation of their metallic state shows interesting phase behaviour (see diagram at right). Plutonium, for example, can reorganise its crystal structure significantly with relatively small changes in temperature, which can alter its density (and volume) by up to 25 percent.
Reference
- ↑ Chang, Raymond, Chemistry (9th ed.), New York: McGraw Hill, 2007.
| 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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| General subfields within the Natural sciences |
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| Astronomy | Biology | Chemistry | Earth science | Ecology | Physics |
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