Atomic No.	Name	Symbol
57	Lanthanum	La
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 lanthanoid (according to IUPAC terminology) (previously lanthanide) series comprises the 15 elements with atomic numbers 57 through 71, from lanthanum to lutetium. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. See also Chemical formula. A chemical symbol is an Abbreviation or shortened version of the name of a Chemical element Lanthanum (ˈlænθənəm is a Chemical element with the symbol La and Atomic number 57 Cerium (ˈsɪəriəm is a Chemical element with the symbol Ce and Atomic number 58 Praseodymium (ˌpreɪzioʊˈdɪmiəm or /ˌpreɪsioʊˈdɪmiəm/ is a Chemical element that has the symbol Pr and Atomic number 59 Neodymium (ˌniːoʊˈdɪmiəm is a Chemical element with the symbol Nd and Atomic number 60 Promethium (prəˈmiːθiəm/ /proʊˈmiːθiəm is a Chemical element with the symbol Pm and Atomic number 61 Samarium (səˈmɛəriəm is a Chemical element with the symbol Sm and Atomic number 62 Europium (jʊˈroʊpiəm is a Chemical element with the symbol Eu and Atomic number 63 Gadolinium (ˌgædəˈlɪniəm is a Chemical element that has the symbol Gd and Atomic number 64 Terbium (ˈtɝbiəm is a Chemical element with the symbol Tb and Atomic number 65 Holmium (ˈhoʊlmiəm is a Chemical element with the symbol Ho and Atomic number 67 Erbium (ˈɝbiəm is a Chemical element with the symbol Er and Atomic number 68 Thulium (ˈθjuːliəm is a Chemical element that has the symbol Tm and Atomic number 69 Lutetium (ljuːˈtiːʃiəm is a Chemical element with the symbol Lu and Atomic number 71 A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. See also List of elements by atomic number In Chemistry and Physics, the atomic number (also known as the proton Lanthanum (ˈlænθənəm is a Chemical element with the symbol La and Atomic number 57 Lutetium (ljuːˈtiːʃiəm is a Chemical element with the symbol Lu and Atomic number 71 ^{[1] [2]} All lanthanoids are f-block elements, corresponding to the filling of the 4f electron shell, except for lutetium which is a d-block lanthanoid. The f-block of the Periodic table of the elements consists of those elements (sometimes referred to as the inner transition elements) for which in the The d-block of the periodic table of the elements consists of those Periodic table groups that contain elements in which in the atomic ground state the highest-energy The lanthanoid series (Ln) is named after lanthanum.

Contents 1 Terminology 2 Chemistry 3 Properties 4 Mnemonics 5 See also 6 External links 7 References

Terminology

The trivial name "rare earths" is sometimes used to describe all the lanthanoids together with scandium and yttrium. In Chemistry and Zoology, a trivial name (also a Common name or vernacular name) is a non- Systematic name. Rare earth elements and rare earth metals are according to IUPAC, the collection of seventeen Chemical elements in the Periodic table, namely Scandium (ˈskændiəm is a Chemical element that has the symbol Sc and Atomic number 21 Yttrium (ˈɪtriəm is a Chemical element with symbol Y and Atomic number 39 The term "rare earths" arises from the minerals from which they were isolated, which were uncommon oxide-type minerals. The use of this name is deprecated by IUPAC, as they are neither rare in abundance nor "earths" (an obsolete term for water-insoluble strongly basic oxides of electropositive metals incapable of being smelted into metal using late 18th century technology). The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element These elements are in fact fairly abundant in nature, although rare as compared to the "common" earths such as lime or magnesia. Cerium is the 26th most abundant element in the Earth's crust, neodymium is more abundant than gold and even thulium (the least common naturally-occurring lanthanoid) is more abundant than iodine^[3]. Despite their abundance, even the technical term "lanthanoids" reflects a sense of elusiveness on the part of these elements, as it comes from the Greek λανθανειν (lanthanein), "to lie hidden. "

IUPAC currently recommends the name lanthanoid rather than lanthanide, as the suffix "-ide" generally indicates negative ions whereas the suffix "-oid" indicates similarity to one of the members of the containing family of elements. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge In the older literature, the name "lanthanon" was often used. There are alternative arrangements of the periodic table that exclude lanthanum or lutetium from appearing together with the other lanthanides.

Chemistry

Lanthanoids are chemically similar to each other. Useful comparison can also be made with the actinoids, where the 5f shell is partially filled. History of the actinoid series From the earlier known chemical properties of actinium (89 up to uranium (92 indicating a relation to the Transition metals it was generally The lanthanoids are typically placed below the main body of the periodic table in the manner of a footnote. The full-width version of the periodic table shows the position of the lanthanoids more clearly. This is a version of the periodic table of the elements that places all elements of one period in the same row

The ionic radii of the lanthanoids decrease through the period — the so-called lanthanoid contraction. The ionic radius, r ion is a measure of the size of an Ion in a Crystal lattice. Except for cerium (III and IV) and europium (III and II), the lanthanides occur as trivalent cations in nature. 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 trace natural materials through physical and chemical processes. In addition, two of the lanthanides have radioactive isotopes with long half-lives (¹⁴⁷Sm and ¹⁷⁶Lu) that date minerals and rocks from Earth, the Moon and meteorites. The lanthanide contraction is responsible for the great geochemical divide that splits the lanthanides into light and heavy-lanthanide enriched minerals, the latter being almost inevitably associated with and dominated by yttrium. This divide is reflected in the first two "rare earths" that were discovered: yttria (1794) and ceria (1803). The divide is driven by the decrease in coordination number as the ionic radius shrinks, and is dramatically illustrated by the two anhydrous phosphate minerals, monazite (monoclinic) and xenotime (tetragonal). The geochemical divide has put more of the light lanthanides in the earths crust, but more of the heavies in the earth's mantle. The result is that although large rich orebodies are found that are enriched in the light lanthanides, correspondingly large orebodies for the heavies are few. The lanthanides obey the Oddo-Harkins rule, which states that odd-numbered elements are less abundant than their even-numbered neighbors. The Oddo-Harkins rule holds that elements with an even Atomic number (such as Carbon) are more common than elements with an odd atomic number (such as

Most lanthanides are widely used in lasers. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. These elements deflect UV and Infrared electromagnetic radiation and are commonly used in the production of sunglass lenses.

Due to their specific electronic configurations, lanthanide atoms tend to lose three electrons, usually 5d¹ and 6s², to attain their most stable oxidation state as trivalent ions.

The lanthanide trications, feature a Xe core electronic configuration with the addition of n 4f electrons, with n varying from 0 [for La(III)] to 14 [for Lu(III)]. This 4fⁿ sub-shell lies inside the ion, shielded by the 5s² and 5p⁶ closed sub-shells. Thus, lanthanide trications are sometimes referred to as “triple-positively charged noble gases”.

The contracted nature of the 4f orbitals, coupled with their small overlap with the ligand atom orbitals, attaches a predominantly ionic character to lanthanide-ligand atom bonds in complexes. Thus, the mainly electrostatic interactions between the lanthanide trication and the atoms of the ligands result in irregular geometric arrangements and a handful of high coordination numbers. Indeed, this triple-positively charged closed shell inert gas electron density characteristic is the foundation of the lanthanide Sparkle Model, used in the computational chemistry of lanthanide complexes. In the context of Atomic orbitals, an open shell is a Valence shell which is not completely filled with Electrons or that has not given all of its valence

Several properties, such as ionization energies, optical properties, magnetic moments and geometries of complexes, etc, serve as proof that the 4f orbitals are indeed wholly shielded from ligand effects.

Lanthanides entering the human body due to exposure to various industrial processes can affect metabolic processes. Trivalent lanthanide ions, especially La³⁺ and Gd³⁺, can interfere with calcium channels in human and animal cells. Lanthanides can also alter or even inhibit the action of various enzymes. Lanthanide ions found in neurons can regulate synaptic transmition, as well as block some receptors (for example, glutamate receptors)^[4].

Properties

All lanthanides closely resemble lanthanum. Lanthanum (ˈlænθənəm is a Chemical element with the symbol La and Atomic number 57 They are electropositive trivalent metals. Electropositivity is a measure of an element's ability to donate Electrons, and therefore form positive Ions. In Chemistry, valence, also known as valency or valency number, is a measure of the number of Chemical bonds formed by the Atoms They are shiny and silvery-white, and tarnish easily when exposed to air. Many make steel. They react violently with most nonmetals. They are relatively soft but their hardness increases with their atomic number. Lanthanides burn in air. They have high melting and boiling points. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid

Mnemonics

To remember the sequence of the lanthanide elements, various mnemonic phrases have been used. A mnemonic device (nəˈmɒnɪk is a Memory aid Commonly met mnemonics are often verbal something such as a very short poem or a special word used to help a person remember The most common one being:

Ladies Can't Put Nickels Properly into Slot-machines. Every Girl Tries Daily, However, Every Time You Look.

See also

• actinoid
• Group number of lanthanoids and actinoids
• rare earth element

External links

• USGS Rare Earths Statistics and Information
• Ana de Bettencourt-Dias: Chemistry of the lanthanides and lanthanide-containing materials

References

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