The alkaline earth metals are six

chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...

s in

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

2 of the periodic table. They are

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

(Be),

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

(Mg),

calcium Calcium is a chemical element with the 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 are most similar t ...

(Ca), strontium (Sr), barium (Ba), and

radium Radium is a chemical element with the symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rathe ...

(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 made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

s at standard temperature and pressure. Structurally, they (together with

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

) 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 cations 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'' (Machel Montano album) * ''Charge!!'', an album by The Aqu ...

+2, and an

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

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 radioisotopes do not decay dire ...

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, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom ...

, 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 radioactivity; thus, the presentation of its properties here is limited. The alkaline earth metals are all silver-colored and soft, and have relatively low

densities Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek language, Greek letter Rho (letter), rho), although the Latin letter ''D'' ca ...

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

s, and boiling points. In chemical terms, all of the alkaline earth metals react with the halogens to form the alkaline earth metal halides, all of which are ionic crystalline compounds (except for

beryllium chloride Beryllium chloride is an inorganic compound with the formula BeCl2. It is a colourless, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to beryllium's diagonal relatio ...

, which is

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

). All the alkaline earth metals except beryllium also react with water to form strongly alkaline

hydroxide Hydroxide is a 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 minor constituent of water. I ...

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 Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule i ...

in their respective periods of the periodic table because of their somewhat low

effective nuclear charge In atomic physics, the effective nuclear charge is the actual amount of positive (nuclear) charge experienced by an electron in a multi-electron atom. The term "effective" is used because the shielding effect of negatively charged electrons prevent ...

s and the ability to attain a full outer shell configuration by losing just two

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s. The second ionization energy of all of the alkaline metals is also somewhat low.

Beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

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 overlap In chemical bonds, an orbital overlap is the concentration of orbitals on adjacent atoms in the same regions of space. Orbital overlap can lead to bond formation. Linus Pauling explained the importance of orbital overlap in the molecular bond ang ...

, 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 with the formula Be F2. This white solid is the principal precursor for the manufacture of beryllium metal. Its structure resembles that of quartz, but BeF2 is highly soluble in water. Properties B ...

, 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

s in their valence shell, so the energetically preferred state of achieving a filled

electron shell In chemistry and atomic physics, an electron shell may be thought of as an orbit followed by electrons around an atom's nucleus. The closest shell to the nucleus is called the "1 shell" (also called the "K shell"), followed by the "2 shell" (or ...

is to lose two electrons to form doubly charged

positive Positive is a property of positivity and may refer to: Mathematics and science * Positive formula, a logical formula not containing negation * Positive number, a number that is greater than 0 * Plus sign, the sign "+" used to indicate a posi ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

Compounds and reactions

The alkaline earth metals all react with the

halogens The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group i ...

to form ionic halides, such as

calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...

(), as well as reacting with

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

to form oxides such as strontium oxide (). Calcium, strontium, and barium react with water to produce

hydrogen gas Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, a ...

and their respective

s (magnesium also reacts, but much more slowly), and also undergo 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 elec ...

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 a nuclide 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; transferr ...

; magnesium and strontium do not. Beryllium-7,

beryllium-10 Beryllium-10 (10Be) is a radioactive isotope of beryllium. It is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen. Beryllium-10 has a half-life of 1.39 × 106 years, and decays by beta decay to stable boron- ...

, and calcium-41 are

trace radioisotope A 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 ...

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 ...

and barium-130 only decay by

double beta decay In nuclear physics, double beta decay is a type of radioactive decay in which two neutrons are simultaneously transformed into two protons, or vice versa, inside an atomic nucleus. As in single beta decay, this process allows the atom to move clos ...

and have very long

half-lives Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

(longer than the

age of the universe In physical cosmology, the age of the universe is the time elapsed since the Big Bang. Astronomers have derived two different measurements of the age of the universe: a measurement based on direct observations of an early state of the universe, ...

) - thus they are

primordial radionuclide In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...

s; and all

isotopes of radium Radium (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of . 226Ra occurs in the decay chain of 238U (often referred ...

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 consi ...

. Calcium-48 is the lightest nuclide to undergo

. 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 (88Ra) has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given. The longest lived, and most common, isotope of radium is 226Ra with a half-life of . 226Ra occurs in the decay chain of 238U (often referre ...

with a half-life of 1600 years; it and

radium-223 Radium-223 (223Ra, Ra-223) is an isotope of radium with an 11.4-day half-life. It was discovered in 1905 by T. Godlewski, a Polish chemist from Kraków, and was historically known as actinium X (AcX). Radium-223 dichloride is an alpha particle- ...

, -224, and -228 occur naturally in the

s of primordial

thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...

and

uranium Uranium is a chemical element with the 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 electrons. Uranium is weak ...

Beryllium-8 Beryllium-8 (8Be, Be-8) is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 8.19 seconds. This has important r ...

is notable by its absence as it nigh instantaneously decays into two

alpha particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be pr ...

s whenever it is formed. The

triple alpha process The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. Triple-alpha process in stars Helium accumulates in the cores of stars as a result of the proton–pro ...

in stars can only occur at energies high enough for beryllium-8 to encounter a third alpha particle before it decays. This is why most

main sequence star Main may refer to: Geography * Main River (disambiguation) **Most commonly the Main (river) in Germany * Main, Iran, a village in Fars Province *"Spanish Main", the Caribbean coasts of mainland Spanish territories in the 16th and 17th centuries ...

s spend billions of years

hydrogen burning Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a ...

but never or only briefly during their red giant phase initiate

helium burning The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei (alpha particles) are transformed into carbon. Triple-alpha process in stars Helium accumulates in the cores of stars as a result of the proton–pr ...

Strontium-90 Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and ...

is a common fission product of the fission of uranium and has been produced in appreciable quantities by humanmade nuclear reactions as well as a tiny

secular equilibrium In nuclear physics, secular equilibrium is a situation in which the quantity of a radioactive isotope remains constant because its production rate (e.g., due to decay of a parent isotope) is equal to its decay rate. In radioactive decay Secular e ...

concentration in uranium due to spontaneous fission. Radioisotopes of alkaline earth metals are usually " bone seekers" as they behave chemically similar to calcium and may do significant harm to bone marrow (a rapidly dividing tissue) when they accumulate there. This property is also made use of in radiotherapy of certain bone cancers as the chemical properties allow the radionuclide to target the cancerous growth in the bone while leaving the rest of the body unharmed. Compared to their neighbors in the periodic table, alkaline earth metals tend to have more stable isotopes, as they possess an even number of protons and for any given even isobar the even-even nuclides are usually more stable than the odd-odd nuclei.

History

Etymology

The alkaline earth metals are named after their oxides, the ''alkaline earths'', whose old-fashioned names were beryllia, magnesia,

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

, strontia, and baria. 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 compounds is attributed to the chemist

Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (

Traité Élémentaire de Chimie ''Traité élémentaire de chimie'' (''Elementary Treatise on Chemistry'') is a textbook written by Antoine Lavoisier published in 1789 and translated into English by Robert Kerr in 1790 under the title ''Elements of Chemistry in a New Systemati ...

'' (''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 Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for t ...

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

have been known and used since prehistoric times. The same is true for the beryllium compounds

beryl Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several ...

and emerald. The other compounds of the alkaline earth metals were discovered starting in the early 15th century. The magnesium compound

magnesium sulfate Magnesium sulfate or magnesium sulphate (in English-speaking countries other than the US) is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, ...

was first discovered in 1618 by a farmer at

Epsom Epsom is the principal town of the Borough of Epsom and Ewell in Surrey, England, about south of central London. The town is first recorded as ''Ebesham'' in the 10th century and its name probably derives from that of a Saxon landowner. The ...

in England. Strontium carbonate was discovered in minerals in the Scottish village of

Strontian Strontian (; gd, Sròn an t-Sìthein) is the main village in Sunart, an area in western Lochaber, Highland, Scotland, on the A861 road. Prior to 1975 it was part of Argyllshire. It lies on the north shore of Loch Sunart, close to the head of ...

in 1790. The last element is the least abundant: radioactive

, which was extracted from

uraninite Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes ...

in 1898. All elements except beryllium were isolated by electrolysis of molten compounds. Magnesium, calcium, and strontium were first produced by

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

Curie In computing, a CURIE (or ''Compact URI'') defines a generic, abbreviated syntax for expressing Uniform Resource Identifiers (URIs). It is an abbreviated URI expressed in a compact syntax, and may be found in both XML and non-XML grammars. A CURIE ...

and

André-Louis Debierne André-Louis Debierne (; 14 July 1874 – 31 August 1949) was a French chemist. He is often considered the discoverer of the element actinium, though H. W. Kirby disputes this and awards credit instead to German chemist Friedrich Oskar Giesel. D ...

also by electrolysis.

Beryllium

Beryl Beryl ( ) is a mineral composed of beryllium aluminium silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several ...

, 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 Prof. Louis Nicolas Vauquelin FRS(For) H FRSE (16 May 1763 – 14 November 1829) was a French pharmacist and chemist. He was the discoverer of both chromium and beryllium. Early life Vauquelin was born at Saint-André-d'Hébertot in Normandy ...

dissolved

aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic an ...

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

with metallic

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...

; this reaction was not able to produce large ingots of beryllium. It was not until 1898, when

Paul Lebeau Paul Marie Alfred Lebeau (19 December 1868 – 18 November 1959) was a French chemist. He studied at the elite École supérieure de physique et de chimie industrielles de la ville de Paris (ESPCI). Together with his doctoral advisor Henri Mo ...

performed an electrolysis of a mixture of

and

sodium fluoride Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. I ...

, that large pure samples of beryllium were produced.

Magnesium

Magnesium was first produced by

in England in 1808 using electrolysis of a mixture of magnesia and

mercuric oxide Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the inorganic compound with the formula Hg O. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form montroydite is v ...

. 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 Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

has been used as a material for building since 7000 to 14,000 BCE, and kilns used for lime have been dated to 2,500 BCE in Khafaja,

Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...

. Calcium as a material has been known since at least the first century, as the

ancient Romans In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 ...

were known to have used

calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...

by preparing it from lime.

Calcium sulfate Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Paris ...

has been known to be able to set broken bones since the tenth century. Calcium itself, however, was not isolated until 1808, when

, in

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

, used electrolysis on a mixture of lime and

, after hearing that

Jöns Jakob Berzelius Jöns is a Swedish given name and a surname. Notable people with the given name include: * Jöns Jacob Berzelius (1779–1848), Swedish chemist * Jöns Budde (1435–1495), Franciscan friar from the Brigittine monastery in NaantaliVallis Grati ...

had prepared a calcium amalgam from the electrolysis of lime in mercury.

Strontium

In 1790, physician

Adair Crawford Adair Crawford FRS FRSE (174829 July 1795), a chemist and physician, was a pioneer in the development of calorimetric methods for measuring the specific heat capacity of substances and the heat of chemical reactions. In his influential 1779 bo ...

discovered ores with distinctive properties, which were named ''strontites'' in 1793 by

Thomas Charles Hope Thomas Charles Hope (21 July 1766 – 13 June 1844) was a British physician, chemist and lecturer. He proved the existence of the element strontium, and gave his name to Hope's Experiment, which shows that water reaches its maximum density a ...

, a chemistry professor at the

University of Glasgow , image = UofG Coat of Arms.png , image_size = 150px , caption = Coat of arms Flag , latin_name = Universitas Glasguensis , motto = la, Via, Veritas, Vita , ...

, who confirmed Crawford's discovery. Strontium was eventually isolated in 1808 by

by electrolysis of a mixture of

strontium chloride Strontium chloride (SrCl2) is a salt of strontium and chlorine. It is a 'typical' salt, forming neutral aqueous solutions. As with all compounds of strontium, this salt emits a bright red colour in flame, and is commonly used in fireworks to that ...

and

. 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 Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist. Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydro ...

, although he was able to isolate only

barium oxide Barium oxide, also known as baria, is a white hygroscopic non-flammable compound with the formula BaO. It has a cubic structure and is used in cathode ray tubes, crown glass, and catalysts. It is harmful to human skin and if swallowed in larg ...

. Barium oxide was isolated again two years later by

Johan Gottlieb Gahn Johan Gottlieb Gahn (19 August 1745 – 8 December 1818) was a Swedish chemist and metallurgist who isolated manganese in 1774. Gahn studied in Uppsala 1762 – 1770 and became acquainted with chemists Torbern Bergman and Carl Wilhelm Scheele. 177 ...

. Later in the 18th century,

William Withering William Withering FRS (17 March 1741 – 6 October 1799) was an English botanist, geologist, chemist, physician and first systematic investigator of the bioactivity of digitalis. Withering was born in Wellington, Shropshire, the son of a surg ...

noticed a heavy mineral in the Cumberland lead mines, which are now known to contain barium. Barium itself was finally isolated in 1808 when

used electrolysis with molten salts, and Davy named the element ''barium'', after

baryta Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium a ...

. Later,

Robert Bunsen Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Bu ...

and

Augustus Matthiessen Augustus Matthiessen, FRS (2 January 1831, in London – 6 October 1870, in London), the son of a merchant, was a British chemist and physicist who obtained his PhD in Germany at the University of Gießen in 1852 with Johann Heinrich Buff. He ...

isolated pure barium by electrolysis of a mixture of barium chloride and ammonium chloride.

Radium

While studying

, on 21 December 1898,

Marie Marie may refer to: People Name * Marie (given name) * Marie (Japanese given name) * Marie (murder victim), girl who was killed in Florida after being pushed in front of a moving vehicle in 1973 * Marie (died 1759), an enslaved Cree person in Tr ...

and

Pierre Curie Pierre Curie ( , ; 15 May 1859 – 19 April 1906) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity, and radioactivity. In 1903, he received the Nobel Prize in Physics with his wife, Marie Curie, and Henri Becq ...

discovered that, even after uranium had decayed, the material created was still radioactive. The material behaved somewhat similarly to

barium compounds Barium is a chemical element with the 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, barium is never found in nature as a free element. Th ...

, 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 In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, th ...

(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 Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the Lanthanides. It was discovered in ...

, 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 Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rare ...

, magnesite, and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

. 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

, 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

, 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

and

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

, 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 mainly in military applications, but non-military uses exist. 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. Beryllium alloys are used for mechanical parts when stiffness, light weight, and dimensional stability are required over a wide temperature range. Beryllium-9 is used in small-scale neutron sources that use the reaction , the reaction used by James Chadwick when he Discovery of the neutron, discovered the neutron. Its low atomic weight and low neutron absorption cross section would make beryllium suitable as a neutron moderator, but its high price and the readily available alternatives such as water, heavy water and nuclear graphite have limited this to niche applications. In the FLiBe eutectic used in molten salt reactors, beryllium's role as a moderator is more incidental than the desired property leading to its use. Magnesium has many uses. It offers advantages over other structural materials such as aluminium, but magnesium's usage is hindered by its flammability. Magnesium is often Magnesium alloy, alloyed with aluminium, zinc and manganese to increase it strength and corrosion resistance. Magnesium has many other industrial applications, such as its role in the production of iron and steel, and in the Kroll process for production of titanium. Calcium is used as a reducing agent in the separation of other metals such as

from ore. It is a major component of many alloys, especially aluminium and copper alloys, and is also used to deoxidize alloys. Calcium has roles in the making of cheese, Mortar (masonry), mortars, and cement. Strontium and barium have fewer applications than the lighter alkaline earth metals. Strontium carbonate is used in the manufacturing of red fireworks. 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 is used in vacuum tubes as a getter to remove gases. Barium sulfate has many uses in the petroleum industry, and other industries. Radium has many former applications based on its radioactivity, but its use is no longer common because of the adverse health effects and long half-life. Radium was frequently used in Radium dial, luminous paints, although this use was stopped after it sickened workers. The nuclear quackery that alleged health benefits of radium formerly led to its addition to drinking water, toothpaste, and many other products. Radium is no longer used even when its radioactive properties are desired because its long half-life makes safe disposal challenging. For example, in Brachytherapy#Radiation sources, brachytherapy, short half-life alternatives such as iridium-192 are usually used instead.

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 2500 °C 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

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. 900°C) In laboratory, they are obtained from hydroxides: :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 2500°C) :CaC₂ + N₂ → CaCN₂ + C :CaCN₂ + H₂SO₄ → CaSO₄ + H₂N—CN :H₂N—CN + H₂O → (H₂N)₂CO (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

, 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 (i.e. Behaves as a " bone seeker") where it bioaccumulation, bioaccumulates with a significant biological half life. While the bones themselves have higher radiation tolerance than other tissues, the rapidly dividing bone marrow does not and can thus be significantly harmed by Sr-90. The effect of ionizing radiation on bone marrow is also the reason why acute radiation syndrome can have anemia-like symptoms and why donation of red blood cells can increase survivability. 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

-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

or strontium instead of barium or

. This noticeably contrasts with periodic trends, which 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.

Explanatory notes

References

Bibliography

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