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The lanthanide or lanthanoid (IUPAC nomenclature) series comprises the fifteen elements with atomic numbers 57 through 71, from lanthanum to lutetium. All lanthanides are f-block elements, corresponding to the filling of the 4f electron shell. Lutetium, which is a d-block element, is also generally considered to be a lanthanide. All lanthanide elements form trivalent cations, Ln3+, whose chemistry is largely determined by the ionic radius, which decreases steadily from lanthanum to lutetium.
The lanthanide elements are the group of elements with atomic number increasing from 57 (lanthanum) to 71 (lutetium). They are termed lanthanide because the lighter elements in the series are chemically similar to lanthanum. Strictly speaking, both lanthanum and lutetium have been labeled as group 3 elements, because they both have a single valence electron in the d shell. However, both elements are often included in any general discussion of the chemistry of the lanthanide elements.
Together with scandium and yttrium, the trivial name "rare earths" is sometimes used to describe all the lanthanides. This name arises from the minerals from which they were isolated, which were uncommon oxide-type minerals. However, the use of the name is deprecated by IUPAC, as the elements 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) . 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 lanthanide) is more abundant than iodine. Despite their abundance, even the technical term "lanthanides" could be interpreted to reflect a sense of elusiveness on the part of these elements, as it comes from the Greek Î»Î±Î½Î¸Î±Î½ÎµÎ¹Î½ (lanthanein), "to lie hidden". However, if not referring to their natural abundance, but rather to their property of "hiding" behind each other in minerals, this interpretation is in fact appropriate. The etymology of the term must be sought in the first discovery of lanthanum, at that time a so-called new rare earth element "lying hidden" in a cerium mineral, but we might call it a fortunate twist of irony that exactly lanthanum was later identified as the first in an entire series of chemically similar elements and could give name to the whole series.
The electronic structure of the lanthanide elements, with minor exceptions is [Xe]6s24fn. In their compounds, the 6s electrons are lost and the ions have the configuration [Xe]4fm. The chemistry of the lanthanides differs from main group elements and transition metals because of the nature of the 4f orbitals. These orbitals are "buried" inside the atom and are shielded from the atom's environment by the 4d and 5p electrons. As a consequence of this, the chemistry of the elements is largely determined by their size, which decreases gradually from 102 pm (La3+) with increasing atomic number to 86 pm (Lu3+), the so-called lanthanide contraction. All the lanthanide elements exhibit the oxidation state +3. In addition Ce3+ can lose its single f electron to form Ce4+ with the stable electronic configuration of xenon. Also, Eu3+ can gain an electron to form Eu2+ with the f7 configuration which has the extra stability of a half-filled shell. Promethium is effectively a man-made element as all its isotopes are radioactive with half-lives of less than 20 y.
The similarity in ionic radius between adjacent lanthanide elements makes it difficult to separate them from each other in naturally occurring ores and other mixtures. Historically the very laborious processes of cascading and fractional crystallization was used. Because the lanthanide ions have slightly different radii, the lattice energy of their salts and hydration energies of the ions will be slightly different, leading to a small difference in solubility. Salts of the formula Ln(NO3)3.2NH4NO3.4H2O can be used. Industrially, the elements are separated from each other by solvent extraction. Typically an aqueous solution of nitrates is extracted into kerosene containing tri-n-butylphosphate, (BunO)3PO. The strength of the complexes formed increases as the ionic radius decreases, so solubility in the organic phase increases. Complete separation can be achieved continuously by use of countercurrent exchange methods. The elements can also be separated by ion-exchange chromatography, making use of the fact that the stability constant for formation of EDTA complexes increases for log K â‰ˆ 15.
The actinides (sometimes called actinoids) occupy the "bottom line" of the periodic tableâ€”a row of elements normally separated from the others, placed at the foot of the chart along with the lanthanides. Both of these families exhibit unusual atomic characteristics, properties that set them apart from the normal sequence on the periodic table. But there is more that distinguishes the actinides, a group of 14 elements along with the transition metal actinium. Only four of them occur in nature, while the other 10 have been produced in laboratories. These 10 are classified, along with the nine elements to the right of actinium on Period 7 of the periodic table, as transuranium (beyond uranium) elements. Few of these elements have important applications in daily life; on the other hand, some of the lower-number transuranium elements do have specialized uses. Likewise several of the naturally occurring actinides are used in areas ranging from medical imaging to powering spacecraft. Then there is uranium, "star" of the actinide series: for centuries it seemed virtually useless; then, in a matter of years, it became the most talked-about element on Earth. Why are actinides and lanthanides set apart from the periodic table? This can best be explained by reference to the transition metals and their characteristics. Actinides and lanthanides are referred to as inner transition metals, because, although they belong to this larger family, they are usually considered separatelyâ€”rather like grown children who have married and started families of their own. The qualities that distinguish the transition metals from the representative or main-group elements on the periodic table are explained in depth within the Transition Metals essay. The reader is encouraged to consult that essay, as well as the one on Families of Elements, which further places the transition metals within the larger context of the periodic table. Here these specifics will be discussed only briefly. The transition metals are distinguished by their configuration of valence electrons, or the outer-shell electrons involved in chemical bonding. Together with the core electrons, which are at lower energy levels, valence electrons move in areas of probability referred to as orbitals. The pattern of orbitals is determined by the principal energy level of the atom, which indicates a distance that an electron may move away from the nucleus. Each principal energy level is divided into sublevels corresponding to the number n of the principal energy level. The actinides, which would be on Period 7 if they were included on the periodic table with the other transition metals, have seven principal energy levels. (Note that period number and principal energy level number are the same.) In the seventh principal energy level, there are seven possible sublevels. The higher the energy level, the larger the number of possible orbital patterns, and the more complex the patterns. Orbital patterns loosely define the overall shape of the electron cloud, but this does not necessarily define the paths along which the electrons move. Rather, it means that if you could take millions of photographs of the electron during a period of a few seconds, the resulting blur of images would describe more or less the shape of a specified orbital. The four basic types of orbital patterns are discussed in the Transition Metals essay, and will not be presented in any detail here. It is important only to know that, unlike the representative elements, transition metals fill the sublevel corresponding to the d orbitals. In addition, they are the only elements that have valence electrons on two different principal energy levels. The lanthanides and actinides are further set apart even from the transition metals, due to the fact that these elements also fill the highly complex f orbitals. Thus these two families are listed by themselves. In most versions of the periodic table, lanthanum (57) is followed by hafnium (72) in the transition metals section of the chart; similarly, actinium (89) is followed by rutherfordium (104). The "missing" metalsâ€”lanthanides and actinides, respectivelyâ€”are shown at the bottom of the chart. The lanthanides can be defined as those metals that fill the 4f orbital. However, because lanthanum (which does not fill the 4f orbital) exhibits similar properties, it is usually included with the lanthanides. Likewise the actinides can be defined as those metals that fill the 5f orbital; but again, because actinium exhibits similar properties, it is usually included with the actinides. One of the distinguishing factors in the actinide family is its great number of radioactive isotopes. Two atoms may have the same number of protons, and thus be of the same element, yet differ in their number of neutronsâ€”neutrally charged patterns alongside the protons at the nucleus. Such atoms are called isotopes, atoms of the same element having different masses. Isotopes are represented symbolically in one of several ways. For instance, there is this format: where S is the chemical symbol of the element, a is the atomic number (the number of protons in its nucleus), and m the mass numberâ€”the sum of protons and neutrons. For the isotope known as uranium-238, for instance, this is shown as. Because the atomic number of any element is established, however, isotopes are usually represented simply with the mass number thus: 238U. They may also be designated with a subscript notation indicating the number of neutrons, so that this information can be obtained at a glance without it being necessary to do the arithmetic. For the uranium isotope shown here, this is written as The term radioactivity describes a phenomenon whereby certain materials are subject to a form of decay brought about by the emission of high-energy particles, or radiation. Types of particles emitted in radiation include: Isotopes are either stable or unstable, with the unstable variety, known as radioisotopes, being subject to radioactive decay. In this context, "decay" does not mean "rot"; rather, a radioisotope decays by turning into another isotope. By continuing to emit particles, the isotope of one element may even turn into the isotope of another element. Eventually the radioisotope becomes a stable isotope, one that is not subject to radioactive decay. This is a process that may take seconds, minutes, hours, days, yearsâ€”and sometimes millions or even billions of years. The rate of decay is gauged by the half-life of a radioisotope sample: in other words, the amount of time it takes for half the nuclei (plural of nucleus) in the sample to become stable. Actinides decay by a process that begins with what is known as K-capture, in which an electron of a radioactive atom is captured by the nucleus and taken into it. This is followed by the splitting, or fission, of the atom's nucleus. This fission produces enormous amounts of energy, as well as the release of two or more neutrons, which may in turn bring about further K-capture. This is called a chain reaction. In the discussion of the actinides that follows, atomic number and chemical symbol will follow the first mention of an element. Atomic mass figures are available on any periodic table, and these will not be mentioned in most cases. The atomic mass figures for actinide elements are very high, as fits their high atomic number, but for most of these, figures are usually for the most stable isotope, which may exist for only a matter of seconds. Though it gives its name to the group as a whole, actinium (Ac, 89) is not a particularly significant element. Discovered in 1902 by German chemist Friedrich Otto Giesel (1852-1927), it is found in uranium ores. Actinium is 150 times more radioactive than radium, a highly radioactive alkaline earth metal isolated around the same time by French-Polish physicist and chemist Marie Curie (1867-1934) and her husband Pierre (1859-1906). More significant than actinium is thorium (Th, 90), first detected in 1815 by the renowned Swedish chemist Jons Berzelius (1779-1848). Berzelius promptly named the element after the Norse god Thor, but eventually concluded tha
actinide series a series of radioactive metallic elements in Group 3 of the periodic table . Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series. The series always includes the 14 elements with atomic numbers 90 through 103. The other members are (in order of increasing atomic number) thorium , protactinium , uranium , neptunium , plutonium , americium , curium , berkelium , californium , einsteinium , fermium , mendelevium , nobelium , and lawrencium . Thorium and uranium are the only actinides found in the earth's crust in appreciable quantities, although small amounts of neptunium and plutonium have been found in uranium ores. Actinium and protactinium are found in nature as decay products of some thorium and uranium isotopes. All the others have only been synthesized in small quantities (see synthetic elements ). Study of the properties of the actinides is hampered by their radioactive instability. It is known, however, that all members of the series resemble actinium and each other in their chemical properties and that they have a strong chemical resemblance to their homologs in the lanthanide series . The actinides are reactive and assume a number of different valences in their compounds. As the atomic number increases in this series, added electrons enter the 5f electron orbital. Elements in this series with atomic numbers greater than that of uranium (92) are called transuranium elements . Elements with atomic numbers greater than 103 are not members of the actinide series; element 104 ( rutherfordium ) is the first of the transactinide elements . Bibliography: See A. J. Freeman and G. H. Lander, ed., Handbook on the Physics and Chemistry of the Actinides (1984); S. Cotton, Lanthanides and Actinides (1991).
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Answers:The actinides have an additional shell of electrons than the lanthanides do.
Answers:You should be asking this in the Chemistry section. They're on two different rows of the periodic table, and whichever one is the bottom of the two will have an additional electron orbital, as one difference. The top one has an single F orbital and the bottom has two F orbitals, I think, but my memory is rusty on this one, try googling the two and seeing what differences you can spot, or ask this elsewhere for better answers.
Answers:The major difference between these two groups is that most of the actinides are not naturally occurring, since they are radioactive with very short half-lives. Lanthanides, also know as the Rare Earth Elements, are due to the filling of the 4f orbital shell and actinides are due to the filling of the 5f orbital shell. Since neodymium and uranium are in the same column of the (combined) lanthanide/actinide rows, they should have similar properties. I am sorry if this answer is to technical for you, but science is technical.
Answers:It's purely a formatting and space saving technique. ************** look at this periodic table. http://www.ptable.com click on the orbitals tab. click on ytterbium.. Yb. lanthanide series... to the right... look at how many "4f" electrons are filled. all of them right? notice Lu is "green" look at it's electron filling pattern. 4f14 5d1.. right?... Now click on element 21 and 39.. Sc and Y. 5d1 electrons.. same pattern as Lu and Lr.. right? Lu and Lr belong in column #3... do you see that? The column headed by element #21, Sc, really looks like this... Sc Y Lu Lr all of the columns of the lanthanide and actinide series fit between columns 2 and 3...get it? the periodic table is compressed to fit on one page.. it it wasn't it would look like this... H.... Li...Be Na..Mg K...Ca.... ........... ........... ...........Sc..Ti Rb..Sr.... ........... ........... ...........Y...Zr Cs..Ba...La..Cr...Pr...