Lanthanides

This edited book Lanthanides is a collection of research chapters, offering an excellent review of recent applications in our lives. It consists of a number of interesting chapters by scientists and researchers from different parts of the world. The book is divided into six chapters. The first chapter is a short introduction that explains the nature and purpose of the book and the logic. The lanthanide series is a unique class of 15 elements with relatively similar chemical properties. They have atomic numbers ranging from 57 to 71, which corresponds to the filling of the 4f orbitals with 14 electrons. The lanthanides are sometimes referred to as the ‘rare earth elements,' leading to the misconception that they are rare.

1. Lanthanide And Actinide Series
2. Lanthanide With Least Mass Element
3. What Are Lanthanides
4. Lanthanides Properties
5. Lanthanides Pronunciation

The lanthanides are the chemical elements found in Row 6 of the periodic table between Groups 3 and 4. They follow lanthanum (La), element #57, which accounts for their family name. The lanthanides include the metals 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).

Lanthanides as rare earth elements

At one time, the lanthanides were called the rare earth elements. The name suggests that chemists once thought that the elements were present in Earth's crust in only very small amounts. As it turns out, with one exception, that assumption was not correct. (That exception is promethium, which was first discovered in the products of a nuclear fission reaction in 1945. Very small amounts of promethium have also been found in naturally occurring ores of uranium.)

The other lanthanides are relatively abundant in Earth's crust. Cerium, for example, is the twenty-sixth most abundant element. Even thulium, the second rarest lanthanide after promethium, is more abundant than iodine.

The point of interest about the lanthanides, then, is not that they are so rare, but that they are so much alike. Most of the lanthanides occur together in nature, and they are very difficult to separate from each other. Indeed, the discovery of the lanthanide elements is one of the most intriguing detective stories in all of chemistry. That story includes episodes in which one element was thought to be another, two elements were identified as one, some elements were mistakenly identified, and so on. By 1907, however, the confusion had been sorted out, and all of the lanthanides (except promethium) had been identified.

Words to Know

Alloy: A mixture of two or more metals with properties different from those of the metals of which it is made.

Catalyst: A material that speeds up the rate of a reaction without undergoing any change in its own composition.

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Monazite: A mineral that constitutes the major source of the lanthanides.

Oxide: A compound containing oxygen and one other element.

Phosphor: A substance that glows when struck by electrons.

Rare earth elements: An older name for the lanthanide elements.

Occurrence

The most important source of the lanthanides is monazite, a heavy dark sand found in Brazil, India, Australia, South Africa, and the United States. The composition of monazite varies depending on its location, but it generally contains about 50 percent of lanthanide compounds by weight. Because of the similarity of their properties and their occurrence together in nature, the lanthanides can be separated from each other and purified only with considerable effort. Consequently, commercial production of the lanthanides tends to be expensive.

Properties

Like most metals, the lanthanides have a bright silvery appearance. Five of the elements (lanthanum, cerium, praseodymium, neodymium, and europium) are very reactive. When exposed to air, they react with oxygen to form an oxide coating that tarnishes the surface. For this reason these metals are stored under mineral oil. The remainder of the lanthanides are not as reactive, and some (gadolinium and lutetium) retain their silvery metallic appearance for a long time.

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When contaminated with nonmetals, such as oxygen or nitrogen, the lanthanides become brittle. They also corrode more easily if contaminated with other metals, such as calcium. Their melting points range from about 819°C (1,506°F) for ytterbium to about 1,663°C (3,025°F) for lutetium. The lanthanides form alloys (mixtures) with many other metals, and these alloys exhibit a wide range of physical properties.

The lanthanides react slowly with cold water and more rapidly with hot water to form hydrogen gas. They burn readily in air to form oxides. They also form compounds with many nonmetals, such as hydrogen, fluorine, phosphorous, sulfur, and chlorine.

Uses of lanthanides

Until fairly recently, the lanthanides had relatively few applications; they cost so much to produce that less expensive alternatives were usually available. The best known lanthanide alloy, Auer metal, is a mixture of cerium and iron that produces a spark when struck. It has long been used as a flint in cigarette and gas lighters. Auer metal is one of a series of mixed lanthanide alloys known as misch metals. The misch metals are composed of varying amounts of the lanthanide metals, mostly cerium and smaller amounts of others such as lanthanum, neodymium, and praseodymium. They have been used to impart strength, hardness, and inertness to structural materials. They have also been used to remove oxygen and sulfur impurities from various industrial systems.

In recent years, less expensive methods have been developed for the production of the lanthanides. As a result, they are now used in a greater variety of applications. One such application is as catalysts, substances that speed up chemical reactions. In the refining industry, for example, the lanthanides are used as catalysts in the conversion of crude oil into gasoline, kerosene, diesel and heating oil, and other products.

The lanthanides are also used as phosphors in color television sets. Phosphors are chemicals that glow with various colors when struck by electrons. For example, oxides of europium and yttrium are used to produce the red colors on a television screen. Other lanthanide compounds are used in streetlights, searchlights, and in the high-intensity lighting present in sports stadiums.

The ceramics industry uses lanthanide oxides to color ceramics and glasses. Optical lenses made with lanthanum oxide are used in cameras and binoculars. Compounds of praseodymium and neodymium are used in glass, such as in television screens, to reduce glare. Cerium oxide has been used to polish glass.

The lanthanides also have a variety of nuclear applications. Because they absorb neutrons, they have been employed in control rods used to regulate nuclear reactors. They have also been used as shielding materials and as structural components in reactors. Some lanthanides have unusual magnetic properties. For instance, cobalt-samarium magnets are very strong permanent magnets.

The Lanthanides consist of the elements in the f-block of period six in the periodic table. While these metals can be considered transition metals, they have properties that set them apart from the rest of the elements.

Introduction

The Lanthanides were first discovered in 1787 when a unusual black mineral was found in Ytterby, Sweden. This mineral, now known as Gadolinite, was later separated into the various Lanthanide elements. In 1794, Professor Gadolin obtained yttria, an impure form of yttrium oxide, from the mineral. In 1803, Berzelius and Klaproth secluded the first Cerium compound. Later, Moseley used an x-ray spectra of the elements to prove that there were fourteen elements between Lanthanum and Hafnium. The rest of the elements were later separated from the same mineral. These elements were first classified as ‘rare earth' due to the fact that obtained by reasonably rare minerals. However, this is can be misleading since the Lanthanide elements have a practically unlimited abundance. The term Lanthanides was adopted, originating from the first element of the series, Lanthanum.

Like any other series in the periodic table, such as the Alkali metals or the Halogens, the Lanthanides share many similar characteristics. These characteristics include the following:

• Similarity in physical properties throughout the series
• Adoption mainly of the +3 oxidation state. Usually found in crystalline compounds)
• They can also have an oxidation state of +2 or +4, though some lanthanides are most stable in the +3 oxidation state.
• Adoption of coordination numbers greater than 6 (usually 8-9) in compounds
• Tendency to decreasing coordination number across the series
• A preference for more electronegative elements (such as O or F) binding
• Very small crystal-field effects
• Little dependence on ligands
• Ionic complexes undergo rapid ligand-exchange

Electron Configuration

Similarly, the Lanthanides have similarities in their electron configuration, which explains most of the physical similarities. These elements are different from the main group elements in the fact that they have electrons in the f orbital. After Lanthanum, the energy of the 4f sub-shell falls below that of the 5d sub-shell. This means that the electron start to fill the 4f sub-shell before the 5d sub-shell.

The electron configurations of these elements were primarily established through experiments. The technique used is based on the fact that each line in an emission spectrum reveals the energy change involved in the transition of an electron from one energy level to another. However, the problem with this technique with respect to the Lanthanide elements is the fact that the 4f and 5d sub-shells have very similar energy levels, which can make it hard to tell the difference between the two.

Another important feature of the Lanthanides is the Lanthanide Contraction, in which the 5s and 5p orbitals penetrate the 4f sub-shell. This means that the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease that continues throughout the series.

Lanthanide And Actinide Series

Properties and Chemical Reactions

One property of the Lanthanides that affect how they will react with other elements is called the basicity. Basicity is a measure of the ease at which an atom will lose electrons. In another words, it would be the lack of attraction that a cation has for electrons or anions. In simple terms, basicity refers to have much of a base a species is. For the Lanthanides, the basicity series is the following:

La³⁺ > Ce³⁺ > Pr³⁺ > Nd³⁺ > Pm³⁺ > Sm³⁺ > Eu³⁺ > Gd³⁺ > Tb³⁺ > Dy³⁺ > Ho³⁺ > Er³⁺ > Tm³⁺ > Yb³⁺ > Lu³⁺

In other words, the basicity decreases as the atomic number increases. Basicity differences are shown in the solubility of the salts and the formation of the complex species. Another property of the Lanthanides is their magnetic characteristics. The major magnetic properties of any chemical species are a result of the fact that each moving electron is a micromagnet. The species are either diamagnetic, meaning they have no unpaired electrons, or paramagnetic, meaning that they do have some unpaired electrons. The diamagnetic ions are: La³⁺, Lu³⁺, Yb²⁺ and Ce⁴⁺. The rest of the elements are paramagnetic.

Metals and their Alloys

The metals have a silvery shine when freshly cut. However, they can tarnish quickly in air, especially Ce, La and Eu. These elements react with water slowly in cold, though that reaction can happen quickly when heated. This is due to their electropositive nature. The Lanthanides have the following reactions:

• oxidize rapidly in moist air
• dissolve quickly in acids
• reaction with oxygen is slow at room temperature, but they can ignite around 150-200 °C
• react with halogens upon heating
• upon heating, react with S, H, C and N

Periodic Trends: Size

Alloy: A mixture of two or more metals with properties different from those of the metals of which it is made.

Catalyst: A material that speeds up the rate of a reaction without undergoing any change in its own composition.

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Monazite: A mineral that constitutes the major source of the lanthanides.

Oxide: A compound containing oxygen and one other element.

Phosphor: A substance that glows when struck by electrons.

Rare earth elements: An older name for the lanthanide elements.

Occurrence

The most important source of the lanthanides is monazite, a heavy dark sand found in Brazil, India, Australia, South Africa, and the United States. The composition of monazite varies depending on its location, but it generally contains about 50 percent of lanthanide compounds by weight. Because of the similarity of their properties and their occurrence together in nature, the lanthanides can be separated from each other and purified only with considerable effort. Consequently, commercial production of the lanthanides tends to be expensive.

Properties

Like most metals, the lanthanides have a bright silvery appearance. Five of the elements (lanthanum, cerium, praseodymium, neodymium, and europium) are very reactive. When exposed to air, they react with oxygen to form an oxide coating that tarnishes the surface. For this reason these metals are stored under mineral oil. The remainder of the lanthanides are not as reactive, and some (gadolinium and lutetium) retain their silvery metallic appearance for a long time.

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When contaminated with nonmetals, such as oxygen or nitrogen, the lanthanides become brittle. They also corrode more easily if contaminated with other metals, such as calcium. Their melting points range from about 819°C (1,506°F) for ytterbium to about 1,663°C (3,025°F) for lutetium. The lanthanides form alloys (mixtures) with many other metals, and these alloys exhibit a wide range of physical properties.

The lanthanides react slowly with cold water and more rapidly with hot water to form hydrogen gas. They burn readily in air to form oxides. They also form compounds with many nonmetals, such as hydrogen, fluorine, phosphorous, sulfur, and chlorine.

Uses of lanthanides

Until fairly recently, the lanthanides had relatively few applications; they cost so much to produce that less expensive alternatives were usually available. The best known lanthanide alloy, Auer metal, is a mixture of cerium and iron that produces a spark when struck. It has long been used as a flint in cigarette and gas lighters. Auer metal is one of a series of mixed lanthanide alloys known as misch metals. The misch metals are composed of varying amounts of the lanthanide metals, mostly cerium and smaller amounts of others such as lanthanum, neodymium, and praseodymium. They have been used to impart strength, hardness, and inertness to structural materials. They have also been used to remove oxygen and sulfur impurities from various industrial systems.

In recent years, less expensive methods have been developed for the production of the lanthanides. As a result, they are now used in a greater variety of applications. One such application is as catalysts, substances that speed up chemical reactions. In the refining industry, for example, the lanthanides are used as catalysts in the conversion of crude oil into gasoline, kerosene, diesel and heating oil, and other products.

The lanthanides are also used as phosphors in color television sets. Phosphors are chemicals that glow with various colors when struck by electrons. For example, oxides of europium and yttrium are used to produce the red colors on a television screen. Other lanthanide compounds are used in streetlights, searchlights, and in the high-intensity lighting present in sports stadiums.

The ceramics industry uses lanthanide oxides to color ceramics and glasses. Optical lenses made with lanthanum oxide are used in cameras and binoculars. Compounds of praseodymium and neodymium are used in glass, such as in television screens, to reduce glare. Cerium oxide has been used to polish glass.

The lanthanides also have a variety of nuclear applications. Because they absorb neutrons, they have been employed in control rods used to regulate nuclear reactors. They have also been used as shielding materials and as structural components in reactors. Some lanthanides have unusual magnetic properties. For instance, cobalt-samarium magnets are very strong permanent magnets.

The Lanthanides consist of the elements in the f-block of period six in the periodic table. While these metals can be considered transition metals, they have properties that set them apart from the rest of the elements.

Introduction

The Lanthanides were first discovered in 1787 when a unusual black mineral was found in Ytterby, Sweden. This mineral, now known as Gadolinite, was later separated into the various Lanthanide elements. In 1794, Professor Gadolin obtained yttria, an impure form of yttrium oxide, from the mineral. In 1803, Berzelius and Klaproth secluded the first Cerium compound. Later, Moseley used an x-ray spectra of the elements to prove that there were fourteen elements between Lanthanum and Hafnium. The rest of the elements were later separated from the same mineral. These elements were first classified as ‘rare earth' due to the fact that obtained by reasonably rare minerals. However, this is can be misleading since the Lanthanide elements have a practically unlimited abundance. The term Lanthanides was adopted, originating from the first element of the series, Lanthanum.

Like any other series in the periodic table, such as the Alkali metals or the Halogens, the Lanthanides share many similar characteristics. These characteristics include the following:

• Similarity in physical properties throughout the series
• Adoption mainly of the +3 oxidation state. Usually found in crystalline compounds)
• They can also have an oxidation state of +2 or +4, though some lanthanides are most stable in the +3 oxidation state.
• Adoption of coordination numbers greater than 6 (usually 8-9) in compounds
• Tendency to decreasing coordination number across the series
• A preference for more electronegative elements (such as O or F) binding
• Very small crystal-field effects
• Little dependence on ligands
• Ionic complexes undergo rapid ligand-exchange

Electron Configuration

Similarly, the Lanthanides have similarities in their electron configuration, which explains most of the physical similarities. These elements are different from the main group elements in the fact that they have electrons in the f orbital. After Lanthanum, the energy of the 4f sub-shell falls below that of the 5d sub-shell. This means that the electron start to fill the 4f sub-shell before the 5d sub-shell.

The electron configurations of these elements were primarily established through experiments. The technique used is based on the fact that each line in an emission spectrum reveals the energy change involved in the transition of an electron from one energy level to another. However, the problem with this technique with respect to the Lanthanide elements is the fact that the 4f and 5d sub-shells have very similar energy levels, which can make it hard to tell the difference between the two.

Another important feature of the Lanthanides is the Lanthanide Contraction, in which the 5s and 5p orbitals penetrate the 4f sub-shell. This means that the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease that continues throughout the series.

Lanthanide And Actinide Series

Properties and Chemical Reactions

One property of the Lanthanides that affect how they will react with other elements is called the basicity. Basicity is a measure of the ease at which an atom will lose electrons. In another words, it would be the lack of attraction that a cation has for electrons or anions. In simple terms, basicity refers to have much of a base a species is. For the Lanthanides, the basicity series is the following:

La³⁺ > Ce³⁺ > Pr³⁺ > Nd³⁺ > Pm³⁺ > Sm³⁺ > Eu³⁺ > Gd³⁺ > Tb³⁺ > Dy³⁺ > Ho³⁺ > Er³⁺ > Tm³⁺ > Yb³⁺ > Lu³⁺

In other words, the basicity decreases as the atomic number increases. Basicity differences are shown in the solubility of the salts and the formation of the complex species. Another property of the Lanthanides is their magnetic characteristics. The major magnetic properties of any chemical species are a result of the fact that each moving electron is a micromagnet. The species are either diamagnetic, meaning they have no unpaired electrons, or paramagnetic, meaning that they do have some unpaired electrons. The diamagnetic ions are: La³⁺, Lu³⁺, Yb²⁺ and Ce⁴⁺. The rest of the elements are paramagnetic.

Metals and their Alloys

The metals have a silvery shine when freshly cut. However, they can tarnish quickly in air, especially Ce, La and Eu. These elements react with water slowly in cold, though that reaction can happen quickly when heated. This is due to their electropositive nature. The Lanthanides have the following reactions:

• oxidize rapidly in moist air
• dissolve quickly in acids
• reaction with oxygen is slow at room temperature, but they can ignite around 150-200 °C
• react with halogens upon heating
• upon heating, react with S, H, C and N

Periodic Trends: Size

The size of the atomic and ionic radii is determined by both the nuclear charge and by the number of electrons that are in the electronic shells. Within those shells, the degree of occupancy will also affect the size. In the Lanthanides, there is a decrease in atomic size from La to Lu. This decrease is known as the Lanthanide Contraction. The trend for the entire periodic table states that the atomic radius decreases as you travel from left to right. Therefore, the Lanthanides share this trend with the rest of the elements.

Color and Light Absorbance

The color that a substance appears is the color that is reflected by the substance. This means that if a substance appears green, the green light is being reflected. The wavelength of the light determines if the light with be reflected or absorbed. Similarly, the splitting of the orbitals can affect the wavelength that can be absorbed. This is turn would be affected by the amount of unpaired electrons.

Occurrence in Nature

Each known Lanthanide mineral contains all the members of the series. However, each mineral contains different concentrations of the individual Lanthanides. The three main mineral sources are the following:

• Monazite: contains mostly the lighter Lanthanides. The commercial mining of monazite sands in the United States is centered in Florida and the Carolinas
• Xenotime: contains mostly the heavier Lanthanides
• Euxenite: contains a fairly even distribution of the Lanthanides

In all the ores, the atoms with a even atomic number are more abundant. This allows for more nuclear stability, as explained in the Oddo-Harkins rule. The Oddo-Harkins rule simply states that the abundance of elements with an even atomic number is greater than the abundance of elements with an odd atomic number. In order to obtain these elements, the minerals must go through a separating process, known as separation chemistry. This can be done with selective reduction or oxidation. Another possibility is an ion-exchange method.

The Oddo-Harkins Rule

The abundance of elements with an even atomic number is greater than the abundance of elements with an odd atomic number.

Lanthanide With Least Mass Element

Applications

Metals and Alloys

The pure metals of the Lanthanides have little use. However, the alloys of the metals can be very useful. For example, the alloys of Cerium have been used for metallurgical applications due to their strong reducing abilities.

Non-nuclear

The Lanthanides can also be used for ceramic purposes. The almost glass-like covering of a ceramic dish can be created with the lanthanides. They are also used to improve the intensity and color balance of arc lights.

Nuclear

Like the Actinides, the Lanthanides can be used for nuclear purposes. The hydrides can be used as hydrogen-moderator carriers. The oxides can be used as diluents in nuclear fields. The metals are good for being used as structural components. The can also be used for structural-alloy-modifying components of reactors. It is also possible for some elements, such as Tm, to be used as portable x-ray sources. Other elements, such as Eu, can be used as radiation sources.

Practice Problems

1. Which elements are considered to be Lanthanides?
2. How do the Lanthanides react with oxygen?
3. What causes the Lanthanide Contraction?
4. Why do Lanthanides exhibit strong electromagnetic and light properties?
5. What do the Lanthanides have in common with the Noble Gases?

What Are Lanthanides

Answers

Lanthanides Properties

1. Elements Lanthanum (57) through Lutetium (71) on the periodic table are considered to be Lanthanides.
2. Lanthanides tend to react with oxygen to form oxides. The reaction at room temperature can be slow while heat can cause the reaction to happen rapidly.
3. The Lanthanide Contraction refers to the decrease in atomic size of the elements in which electrons fill the f-subshell. Since the f sub-shell is not shielded, the atomic size will decrease as the nuclear charge still increases.
4. Lanthanides exhibit strong electromagnetic and light properties because of the presence of unpaired electrons in the f-orbitals. The majority of the Lanthanides are paramagnetic, which means that they have strong magnetic fields.
5. Both the Lanthanides and Noble Gases tend to bind with more electronegative atoms, such as Oxygen or Fluorine.

References

Lanthanides Pronunciation

1. Petrucci, Hardwood, Herring. 'General Chemistry: Principles & Modern Applications'. New Jersey: Macmillan Publishing Company, 2007.
2. Moeller, Therald. The Chemistry of the Lanthanides. New York: Reinhold Publishing Corporation, 1963.
3. Cotton, Simon. Lanthanides and Actinides. London: Macmillan Education Ltd, 1991.