Alkaline earth metal
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The alkaline earth metals are six
chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nu ...
s in
group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with ...
2 of the
periodic table The periodic table, also known as the periodic table of elements, is a tabular display of the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry ...

periodic table
. They are
beryllium Beryllium is a chemical element with the Symbol (chemistry), symbol Be and atomic number 4. It is a Abundance of the chemical elements#Universe, relatively rare element in the universe, usually occurring as a product of the spallation of larger ...
(Be),
magnesium Magnesium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

magnesium
(Mg),
calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties a ...

calcium
(Ca),
strontium Strontium is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

strontium
(Sr),
barium Barium is a chemical element with the Symbol (chemistry), symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical Reactivity (chemistry), reactivity, bar ...
(Ba), and
radium Radium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

radium
(Ra).. The elements have very similar properties: they are all shiny, silvery-white, somewhat
reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a Bowling ball#Coverstock technology, bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reacti ...
metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Electrical resistivity and conductivity, el ...

metal
s at
standard temperature and pressure Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined relationship to a unit ...
. Structurally, they (together with
helium Helium (from el, ἥλιος, Helios, lit=Sun) is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting ...

helium
) have in common an outer s-orbital which is full; that is, this orbital contains its full complement of two electrons, which the alkaline earth metals readily lose to form
cation An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered negative by convention and this charge is equal and opposite to charge of a proton, which is considered positive by convent ...
s with
charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge'' (David Ford album) * Charge (Machel Montano album), ''Charge'' (Mac ...
+2, and an
oxidation state The oxidation state, or oxidation number, is the hypothetical charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge' ...
of +2. All the discovered alkaline earth metals occur in nature, although radium occurs only through the
decay chain In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most Radionuclide, radioisotopes do not de ...
of uranium and thorium and not as a primordial element. There have been experiments, all unsuccessful, to try to synthesize element 120, the next potential member of the group.


Characteristics


Chemical

As with other groups, the members of this family show patterns in their
electronic configuration In atomic physics and quantum chemistry Quantum chemistry, also called molecular quantum mechanics, is a branch of chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
, especially the outermost shells, resulting in trends in chemical behavior: Most of the chemistry has been observed only for the first five members of the group. The chemistry of radium is not well-established due to its ; thus, the presentation of its properties here is limited. The alkaline earth metals are all silver-colored and soft, and have relatively low
densities The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...
,
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase exist in Thermodynamic equilibrium, equilibrium. ...

melting point
s, and
boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding enviro ...
s. In chemical terms, all of the alkaline earth metals react with the
halogen The halogens () are a group in the periodic table consisting of five chemically related elements: fluorine Fluorine is a chemical element with the Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standar ...

halogen
s to form the alkaline earth metal
halide A halide is a binary phase, of which one part is a halogen The halogens () are a group in the periodic table consisting of five chemically related elements: fluorine Fluorine is a chemical element with the Chemical symbol, symbol F and ato ...
s, all of which are ionic crystalline compounds (except for
beryllium chloride Beryllium chloride is an inorganic compound with the chemical formula, formula BeCl2. It is a colourless, hygroscopy, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to Be ...

beryllium chloride
, which is
covalent A covalent bond is a chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the Coulomb's law, electrostatic force of attraction bet ...
). All the alkaline earth metals except beryllium also react with water to form strongly
alkali In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they ...
ne
hydroxide Hydroxide is a polyatomic ion, diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually Self-ionization o ...
s and, thus, should be handled with great care. The heavier alkaline earth metals react more vigorously than the lighter ones. The alkaline earth metals have the second-lowest first ionization energies in their respective periods of the
periodic table The periodic table, also known as the periodic table of elements, is a tabular display of the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry ...

periodic table
because of their somewhat low
effective nuclear charge The effective nuclear charge (often symbolized as Z_ or Z^\ast) is the net positive charge experienced by an electron The electron is a subatomic particle, symbol or , whose electric charge Electric charge is the physical property of mat ...

effective nuclear charge
s and the ability to attain a
full outer shell In atomic physics and quantum chemistry Quantum chemistry, also called molecular quantum mechanics, is a branch of chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compound ...
configuration by losing just two
electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has ma ...
s. The second ionization energy of all of the alkaline metals is also somewhat low.
Beryllium Beryllium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...
is an exception: It does not react with water or steam, and its halides are covalent. If beryllium did form compounds with an ionization state of +2, it would polarize electron clouds that are near it very strongly and would cause extensive
orbital overlapIn chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the Coulomb's law, electrostatic force of attraction between oppositely charged i ...

orbital overlap
, since beryllium has a high charge density. All compounds that include beryllium have a covalent bond. Even the compound
beryllium fluoride Beryllium fluoride is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, p ...
, which is the most ionic beryllium compound, has a low melting point and a low electrical conductivity when melted. All the alkaline earth metals have two
electron The electron is a subatomic particle In physical sciences, subatomic particles are smaller than atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has ma ...
s in their valence shell, so the energetically preferred state of achieving a filled
electron shell In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they un ...
is to lose two electrons to form doubly charged
positive Positive is a property of Positivity (disambiguation), positivity and may refer to: Mathematics and science * Converging lens or positive lens, in optics * Plus sign, the sign "+" used to indicate a positive number * Positive (electricity), a po ...
ion An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascribed several physical property, physical or ...
s.


Compounds and reactions

The alkaline earth metals all react with the
halogens The halogens () are a group in the periodic table The periodic table, also known as the periodic table of elements, is a tabular display of the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The ...

halogens
to form ionic halides, such as
calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2. It is a white coloured crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calc ...
(), as well as reacting with
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
to form oxides such as
strontium oxide Strontium oxide or strontia, SrO, is formed when strontium Strontium is the chemical element with the symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, Object (philosophy), object, ...
(). Calcium, strontium, and barium react with water to produce
hydrogen gas Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...
and their respective
hydroxide Hydroxide is a polyatomic ion, diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually Self-ionization o ...
s (magnesium also reacts, but much more slowly), and also undergo
transmetalationTransmetalation (alt. spelling: transmetallation) is a type of organometallic reaction that involves the transfer of ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form ...

transmetalation
reactions to exchange
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...
s.
:


Physical and atomic

The table below is a summary of the key physical and atomic properties of the alkaline earth metals.


Nuclear stability

Of the six alkaline earth metals, beryllium, calcium, barium, and radium have at least one naturally occurring
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred ...
; magnesium and strontium do not. Beryllium-7,
beryllium-10 Beryllium-10 (10Be) is a radioactive isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but diffe ...
, and calcium-41 are
trace radioisotopeA trace radioisotope is a radioisotope that occurs naturally in trace amounts (i.e. extremely small). Generally speaking, trace radioisotopes have half-lives that are short in comparison with the age of the Earth, since primordial nuclides tend to o ...
s;
calcium-48 Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so t ...

calcium-48
and barium-130 have very long
half-lives Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents a ...
and thus are
primordial radionuclide In geochemistry Geochemistry is the science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, ...
s; and all
isotopes of radium Radium Radium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the ...
are
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

radioactive
. Calcium-48 is the lightest nuclide to undergo
double beta decay In nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions. Other forms of nuclear matter are also studied. Nuclear physics should not be confused with atomic physics, which studi ...
. Calcium and barium are weakly radioactive: calcium contains about 0.1874% calcium-48, and barium contains about 0.1062% barium-130. The longest lived isotope of radium is
radium-226 Radium Radium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the ...

radium-226
with a half-life of 1600 years; it and
radium-223 Radium-223 (223Ra, Ra-223) is an isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different ...

radium-223
, -224, and -228 occur naturally in the
decay chain In nuclear science Nuclear physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, it ...
s of primordial
thorium Thorium is a weakly radioactive decay, radioactive metallic chemical element with the Symbol (chemistry), symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderatel ...

thorium
and
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence elect ...

uranium
.


History


Etymology

The alkaline earth metals are named after their
oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
s, the ''alkaline earths'', whose old-fashioned names were
beryllia Beryllium oxide (BeO), also known as beryllia, is an inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: thei ...
, Magnesium oxide, magnesia, Calcium oxide, lime, strontia, and baryta. These oxides are basic (alkaline) when combined with water. "Earth" was a term applied by early chemists to nonmetallic substances that are insoluble in water and resistant to heating—properties shared by these oxides. The realization that these earths were not elements but chemical compound, compounds is attributed to the chemist Antoine Lavoisier. In his ''Traité Élémentaire de Chimie'' (''Elements of Chemistry'') of 1789 he called them salt-forming earth elements. Later, he suggested that the alkaline earths might be metal oxides, but admitted that this was mere conjecture. In 1808, acting on Lavoisier's idea, Humphry Davy became the first to obtain samples of the metals by electrolysis of their molten earths, thus supporting Lavoisier's hypothesis and causing the group to be named the ''alkaline earth metals''.


Discovery

The calcium compounds calcite and Lime (material), lime have been known and used since prehistoric times. The same is true for the beryllium compounds beryl and emerald. The other compounds of the alkaline earth metals were discovered starting in the early 15th century. The magnesium compound magnesium sulfate was first discovered in 1618 by a farmer at Epsom in England. Strontium carbonate was discovered in minerals in the Scottish village of Strontian in 1790. The last element is the least abundant: radioactive
radium Radium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

radium
, which was extracted from uraninite in 1898. All elements except beryllium were isolated by electrolysis of molten compounds. Magnesium, calcium, and strontium were first produced by Humphry Davy in 1808, whereas beryllium was independently isolated by Friedrich Wöhler and Antoine Bussy in 1828 by reacting beryllium compounds with potassium. In 1910, radium was isolated as a pure metal by Marie Curie, Curie and André-Louis Debierne also by electrolysis.


Beryllium

Beryl, a mineral that contains beryllium, has been known since the time of the Ptolemaic Kingdom in Egypt. Although it was originally thought that beryl was an aluminium silicate, beryl was later found to contain a then-unknown element when, in 1797, Louis-Nicolas Vauquelin dissolved aluminium hydroxide from beryl in an alkali. In 1828, Friedrich Wöhler and Antoine Bussy independently isolated this new element, beryllium, by the same method, which involved a reaction of
beryllium chloride Beryllium chloride is an inorganic compound with the chemical formula, formula BeCl2. It is a colourless, hygroscopy, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to Be ...

beryllium chloride
with metallic potassium; this reaction was not able to produce large ingots of beryllium. It was not until 1898, when Paul Lebeau performed an electrolysis of a mixture of
beryllium fluoride Beryllium fluoride is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, p ...
and sodium fluoride, that large pure samples of beryllium were produced.


Magnesium

Magnesium was first produced by Humphry Davy in England in 1808 using electrolysis of a mixture of magnesia and Mercury(II) oxide, mercuric oxide. Antoine Bussy prepared it in coherent form in 1831. Davy's first suggestion for a name was magnium, but the name magnesium is now used.


Calcium

Lime (material), Lime has been used as a material for building since 7000 to 14,000 BCE, and Lime kiln, kilns used for lime have been dated to 2,500 BCE in Khafaja, Mesopotamia. Calcium as a material has been known since at least the first century, as the Ancient Rome, ancient Romans were known to have used calcium oxide by preparing it from lime. Calcium sulfate has been known to be able to set broken bones since the tenth century. Calcium itself, however, was not isolated until 1808, when Humphry Davy, in England, used electrolysis on a mixture of lime and mercuric oxide, after hearing that Jöns Jakob Berzelius had prepared a calcium amalgam from the electrolysis of lime in mercury.


Strontium

In 1790, physician Adair Crawford discovered ores with distinctive properties, which were named ''strontites'' in 1793 by Thomas Charles Hope, a chemistry professor at the University of Glasgow, who confirmed Crawford's discovery. Strontium was eventually isolated in 1808 by Humphry Davy by electrolysis of a mixture of strontium chloride and mercuric oxide. The discovery was announced by Davy on 30 June 1808 at a lecture to the Royal Society.


Barium

Barite, a mineral containing barium, was first recognized as containing a new element in 1774 by Carl Scheele, although he was able to isolate only barium oxide. Barium oxide was isolated again two years later by Johan Gottlieb Gahn. Later in the 18th century, William Withering noticed a heavy mineral in the Cumberland lead mines, which are now known to contain barium. Barium itself was finally isolated in 1808 when Humphry Davy used electrolysis with molten salts, and Davy named the element ''barium'', after baryta. Later, Robert Bunsen and Augustus Matthiessen isolated pure barium by electrolysis of a mixture of barium chloride and ammonium chloride.


Radium

While studying uraninite, on 21 December 1898, Marie Curie, Marie and Pierre Curie discovered that, even after uranium had decayed, the material created was still radioactive. The material behaved somewhat similarly to Compounds of barium, barium compounds, although some properties, such as the color of the flame test and spectral lines, were much different. They announced the discovery of a new element on 26 December 1898 to the French Academy of Sciences. Radium was named in 1899 from the word ''radius'', meaning ''ray'', as radium emitted power in the form of rays.


Occurrence

Beryllium occurs in the earth's crust at a concentration of two to six parts per million (ppm), much of which is in soils, where it has a concentration of six ppm. Beryllium is one of the rarest elements in seawater, even rarer than elements such as scandium, with a concentration of 0.2 parts per trillion. However, in freshwater, beryllium is somewhat more common, with a concentration of 0.1 parts per billion. Magnesium and calcium are very common in the earth's crust, being respectively the fifth- eighth-most-abundant elements. None of the alkaline earth metals are found in their elemental state. Common magnesium—containing minerals are carnallite, magnesite, and Dolomite (mineral), dolomite. Common calcium-containing minerals are chalk, limestone, gypsum, and anhydrite. Strontium is the fifteenth-most-abundant element in the Earth's crust. The principal minerals are celestite and strontianite. Barium is slightly less common, much of it in the mineral barite. Radium, being a decay product of
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence elect ...

uranium
, is found in all uranium-bearing ores."Radium"
, Los Alamos National Laboratory. Retrieved on 2009-08-05.
Due to its relatively short half-life, radium from the Earth's early history has decayed, and present-day samples have all come from the much slower decay of uranium.


Production

Most beryllium is extracted from beryllium hydroxide. One production method is sintering, done by mixing beryl, sodium fluorosilicate, and soda at high temperatures to form sodium fluoroberyllate, aluminium oxide, and silicon dioxide. A solution of sodium fluoroberyllate and sodium hydroxide in properties of water, water is then used to form beryllium hydroxide by precipitation. Alternatively, in the melt method, powdered beryl is heated to high temperature, cooled with water, then heated again slightly in sulfuric acid, eventually yielding beryllium hydroxide. The beryllium hydroxide from either method then produces
beryllium fluoride Beryllium fluoride is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, p ...
and
beryllium chloride Beryllium chloride is an inorganic compound with the chemical formula, formula BeCl2. It is a colourless, hygroscopy, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to Be ...

beryllium chloride
through a somewhat long process. Electrolysis or heating of these compounds can then produce beryllium. In general, strontium carbonate is extracted from the mineral celestite through two methods: by leaching the celestite with sodium carbonate, or in a more complicated way involving coal. To produce barium, barite (impure barium sulfate) is converted to barium sulfide by carbothermic reduction (such as with Coke (fuel), coke). The sulfide is water-soluble and easily reacted to form pure barium sulfate, used for commercial pigments, or other compounds, such as barium nitrate. These in turn are calcined into barium oxide, which eventually yields pure barium after reduction with aluminium. The most important supplier of barium is China, which produces more than 50% of world supply.


Applications

Beryllium is used mostly for military applications, but there are other uses of beryllium, as well. In electronics, beryllium is used as a p-type semiconductor, p-type dopant in some semiconductors, and beryllium oxide is used as a high-strength electrical insulator and heat conductor. Due to its light weight and other properties, beryllium is also used in mechanics when stiffness, light weight, and dimensional stability are required at wide temperature ranges. Magnesium has many uses. It offers advantages over other materials such as aluminium, although this usage has fallen out of favor due to magnesium's flammability. Magnesium is also often alloyed with aluminium or zinc to form materials with more desirable properties than any pure metal. Magnesium has many other uses in industrial applications, such as having a role in the production of iron and steel, and the production of titanium. Calcium also has many uses. One of its uses is as a reducing agent in the separation of other metals from ore, such as
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence elect ...

uranium
. It is also used in the production of the alloys of many metals, such as aluminium and copper alloys, and is also used to deoxidize alloys as well. Calcium also has a role in the making of cheese, Mortar (masonry), mortars, and cement. Strontium and barium do not have as many applications as the lighter alkaline earth metals, but still have uses. Strontium carbonate is often used in the manufacturing of red fireworks, and pure strontium is used in the study of neurotransmitter release in neurons. Radioactive strontium-90 finds some use in Radioisotope thermoelectric generator, RTGs, which utilize its decay heat. Barium has some use in vacuum tubes to remove gases, and barium sulfate has many uses in the petroleum industry, as well as other industries. Due to its radioactivity, radium no longer has many applications, but it used to have many. Radium used to be used often in luminous paints, although this use was stopped after workers got sick. As people used to think that radioactivity was a good thing, radium used to be added to drinking water, toothpaste, and many other products, although they are also not used anymore due to their health effects. Radium is no longer even used for its radioactive properties, as there are more powerful and safer emitters than radium.


Representative reactions of alkaline earth metals

''Reaction with halogens'' :Ca + Cl2 → CaCl2 Anhydrous calcium chloride is a hygroscopic substance that is used as a desiccant. Exposed to air, it will absorb water vapour from the air, forming a solution. This property is known as deliquescence. ''Reaction with oxygen'' :Ca + 1/2O2 → CaO :Mg + 1/2O2 → MgO ''Reaction with sulphur'' :Ca + 1/8S8 → CaS ''Reaction with carbon'' With carbon, they form acetylides directly. Beryllium forms carbide. :2Be + C → Be2C :CaO + 3C → CaC2 + CO (at 25000C in furnace) :CaC2 + 2H2O → Ca(OH)2 + C2H2 :Mg2C3 + 4H2O → 2Mg(OH)2 + C3H4 ''Reaction with nitrogen'' Only Be and Mg form nitrides directly. :3Be + N2 → Be3N2 :3Mg + N2 → Mg3N2 ''Reaction with hydrogen'' Alkaline earth metals react with hydrogen to generate saline hydride that are unstable in water. :Ca + H2 → CaH2 ''Reaction with water'' Ca, Sr and Ba readily react with water to form
hydroxide Hydroxide is a polyatomic ion, diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually Self-ionization o ...
and hydrogen gas. Be and Mg are Passivation (chemistry), passivated by an impervious layer of oxide. However, amalgamated magnesium will react with water vapour. :Mg + H2O → MgO + H2 ''Reaction with acidic oxides'' Alkaline earth metals reduce the nonmetal from its oxide. :2Mg + SiO2 → 2MgO + Si :2Mg + CO2 → 2MgO + C (in solid carbon dioxide) ''Reaction with acids'' :Mg + 2HCl → MgCl2 + H2 :Be + 2HCl → BeCl2 + H2 ''Reaction with bases'' Be exhibits amphoteric properties. It dissolves in concentrated sodium hydroxide. :Be + NaOH + 2H2O → Na[Be(OH)3] + H2 ''Reaction with alkyl halides'' Magnesium reacts with alkyl halides via an insertion reaction to generate Grignard reagents. :RX + Mg → RMgX (in anhydrous ether)


Identification of alkaline earth cations

''The flame test'' The table below presents the colours observed when the flame of a Bunsen burner is exposed to salts of alkaline earth metals. Be and Mg do not impart colour to the flame due to their small size. ''In solution'' Mg2+ Disodium phosphate is a very selective reagent for magnesium ions and, in the presence of ammonium salts and ammonia, forms a white precipitate of ammonium magnesium phosphate. :Mg2+ + NH3 + Na2HPO4 → (NH4)MgPO4 + 2Na+ Ca2+ Ca2+ forms a white precipitate with ammonium oxalate. Calcium oxalate is insoluble in water, but is soluble in mineral acids. :Ca2+ + (COO)2(NH4)2 → (COO)2Ca + NH4+ Sr2+ Strontium ions precipitate with soluble sulphate salts. :Sr2+ + Na2SO4 → SrSO4 + 2Na+ All ions of alkaline earth metals form white precipitate with ammonium carbonate in the presence of ammonium chloride and ammonia.


Compounds of alkaline earth metals

''Oxides'' The alkaline earth metal oxides are formed from the thermal decomposition of the corresponding carbonates. :CaCO3 → CaO + CO2 (at approx. 9000C) In laboratory, they are obtained from calcium: :Mg(OH)2 → MgO + H2O or nitrates: :Ca(NO3)2 → CaO + 2NO2 + 1/2O2 The oxides exhibit basic character: they turn phenolphthalein red and litmus, blue. They react with water to form hydroxides in an exothermic reaction. :CaO + H2O → Ca(OH)2 + Q Calcium oxide reacts with carbon to form acetylide. :CaO + 3C → CaC2 + CO (at 25000) :CaC2 + N2 → CaCN2 + C :CaCN2 + H2SO4 → CaSO4 + H2N—CN :H2N—CN + H2O → (H2N)CO (urea) :CaCN2 + 2H2O → CaCO3 + NH3 ''Hydroxides'' They are generated from the corresponding oxides on reaction with water. They exhibit basic character: they turn phenolphthalein pink and litmus, blue. Beryllium hydroxide is an exception as it exhibits amphoteric character. :Be(OH)2 + 2HCl → BeCl2 + H2O :Be(OH)2 + NaOH → Na[Be(OH)3] ''Salts'' Ca and Mg are found in nature in many compounds such as Dolomite (mineral), dolomite, aragonite, magnesite (carbonate rocks). Calcium and magnesium ions are found in hard water. Hard water represents a multifold issue. It is of great interest to remove these ions, thus softening the water. This procedure can be done using reagents such as calcium hydroxide, sodium carbonate or sodium phosphate. A more common method is to use ion-exchange aluminosilicates or ion-exchange resins that trap Ca2+ and Mg2+ and liberate Na+ instead: :Na2O·Al2O3·6SiO2 + Ca2+ → CaO·Al2O3·6SiO2 + 2Na+


Biological role and precautions

Magnesium and calcium are ubiquitous and essential to all known living organisms. They are involved in more than one role, with, for example, magnesium or calcium ion transporter, ion pumps playing a role in some cellular processes, magnesium functioning as the active center in some enzymes, and calcium salts taking a structural role, most notably in bones. Strontium plays an important role in marine aquatic life, especially hard corals, which use strontium to build their exoskeletons. It and barium have some uses in medicine, for example "barium meals" in radiographic imaging, whilst strontium compounds are employed in some toothpastes. Excessive amounts of strontium-90 are toxic due to its radioactivity and strontium-90 mimics calcium and then can kill. Beryllium and radium, however, are toxic. Beryllium's low aqueous solubility means it is rarely available to biological systems; it has no known role in living organisms and, when encountered by them, is usually highly toxic. Radium has a low availability and is highly radioactive, making it toxic to life.


Extensions

The next alkaline earth metal after radium is thought to be element 120, although this may not be true due to relativistic quantum chemistry, relativistic effects. The synthesis of element 120 was first attempted in March 2007, when a team at the Flerov Laboratory of Nuclear Reactions in Dubna bombarded plutonium-244 with iron-58 ions; however, no atoms were produced, leading to a limit of 400 barn (unit), fb for the cross-section at the energy studied. In April 2007, a team at the Gesellschaft für Schwerionenforschung, GSI attempted to create element 120 by bombarding
uranium Uranium is a chemical element with the Symbol (chemistry), symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence elect ...

uranium
-238 with nickel-64, although no atoms were detected, leading to a limit of 1.6 pb for the reaction. Synthesis was again attempted at higher sensitivities, although no atoms were detected. Other reactions have been tried, although all have been met with failure.http://fias.uni-frankfurt.de/kollo/Duellmann_FIAS-Kolloquium.pdf The chemistry of element 120 is predicted to be closer to that of
calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties a ...

calcium
or
strontium Strontium is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

strontium
instead of
barium Barium is a chemical element with the Symbol (chemistry), symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical Reactivity (chemistry), reactivity, bar ...
or
radium Radium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same nu ...

radium
. This is unusual as periodic trends would predict element 120 to be more reactive than barium and radium. This lowered reactivity (chemistry), reactivity is due to the expected energies of element 120's valence electrons, increasing element 120's ionization energy and decreasing the metallic radius, metallic and ionic radius, ionic radii. The next alkaline earth metal after element 120 has not been definitely predicted. Although a simple extrapolation using the Aufbau principle would suggest that element 170 is a congener of 120, relativistic quantum chemistry, relativistic effects may render such an extrapolation invalid. The next element with properties similar to the alkaline earth metals has been predicted to be element 166, though due to overlapping orbitals and lower energy gap below the 9s subshell, element 166 may instead be placed in group 12 element, group 12, below copernicium.


Notes


References


Bibliography

*


Further reading


Group 2 – Alkaline Earth Metals
Royal Chemistry Society. * Hogan, C.Michael. 2010
''Calcium''. eds. A.Jorgensen, C. Cleveland. Encyclopedia of Earth
National Council for Science and the Environment. * Maguire, Michael E. "Alkaline Earth Metals." ''Chemistry: Foundations and Applications''. Ed. J. J. Lagowski. Vol. 1. New York: Macmillan Reference USA, 2004. 33–34. 4 vols. Gale Virtual Reference Library. Thomson Gale. * Silberberg, M.S., Chemistry: The molecular nature of Matter and Change (3e édition, McGraw-Hill 2009) * Petrucci R.H., Harwood W.S. et Herring F.G., General Chemistry (8e édition, Prentice-Hall 2002) {{DEFAULTSORT:Alkaline Earth Metal Alkaline earth metals, Periodic table Groups (periodic table)