Calcium

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Calcium,  ₂₀Ca

Calcium
Appearance	dull gray, silver; with a pale yellow tint
Standard atomic weight Ar, std(Ca)	40.078(4)
Calcium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Mg ↑ Ca ↓ Sr potassium ← calcium → scandium
Atomic number (Z)	20
Group	group 2 (alkaline earth metals)
Period	period 4
Block	s-block
Element category	alkaline earth metal
Electron configuration	[Ar] 4s2
Electrons per shell	2, 8, 8, 2
Physical properties
Phase at STP	solid
Melting point	1115 K ​(842 °C, ​1548 °F)
Boiling point	1757 K ​(1484 °C, ​2703 °F)
Density (near r.t.)	1.55 g/cm3
when liquid (at m.p.)	1.378 g/cm3
Heat of fusion	8.54 kJ/mol
Heat of vaporisation	154.7 kJ/mol
Molar heat capacity	25.929 J/(mol·K)
Vapour pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 864 956 1071 1227 1443 1755
Atomic properties
Oxidation states	+1, +2 (a strongly basic oxide)
Electronegativity	Pauling scale: 1.00
Ionisation energies	1st: 589.8 kJ/mol 2nd: 1145.4 kJ/mol 3rd: 4912.4 kJ/mol
Atomic radius	empirical: 197 pm
Covalent radius	176±10 pm
Van der Waals radius	231 pm
Spectral lines of calcium
Other properties
Natural occurrence	primordial
Crystal structure	​face-centred cubic (fcc)
Speed of sound thin rod	3810 m/s (at 20 °C)
Thermal expansion	22.3 µm/(m·K) (at 25 °C)
Thermal conductivity	201 W/(m·K)
Electrical resistivity	33.6 nΩ·m (at 20 °C)
Magnetic ordering	diamagnetic
Magnetic susceptibility	+40.0·10−6 cm3/mol
Young's modulus	20 GPa
Shear modulus	7.4 GPa
Bulk modulus	17 GPa
Poisson ratio	0.31
Mohs hardness	1.75
Brinell hardness	170–416 MPa
CAS Number	7440-70-2
History
Discovery and first isolation	Humphry Davy (1808)
Main isotopes of calcium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 40Ca 96.941% stable 41Ca trace 1.03×105 y ε 41K 42Ca 0.647% stable 43Ca 0.135% stable 44Ca 2.086% stable 45Ca syn 162.7 d β− 45Sc 46Ca 0.004% stable 47Ca syn 4.5 d β− 47Sc γ – 48Ca 0.187% 6.4×1019 y β−β− 48Ti

Calcium is a chemical element with 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 to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are widely used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, and in the manufacture of soaps. On the other hand, the metal in pure form has few applications due to its high reactivity; still, in small quantities it is often used as an alloying component in steelmaking, and sometimes, as a calcium–lead alloy, in making automotive batteries.

Calcium is the most abundant metal and the fifth-most abundant element in the human body. As electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger; in neurotransmitter release from neurons; in contraction of all muscle cell types; as cofactors in many enzymes; and in fertilization. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation.

Characteristics

Classification

Calcium is a very ductile silvery metal (sometimes described as pale yellow) whose properties are very similar to the heavier elements in its group, strontium, barium, and radium. A calcium atom has twenty electrons, arranged in the electron configuration [Ar]4s². Like the other elements placed in group 2 of the periodic table, calcium has two valence electrons in the outermost s-orbital, which are very easily lost in chemical reactions to form a dipositive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is almost always divalent in its compounds, which are usually ionic. Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX₂ is much higher than those of the hypothetical MX. This occurs because of the much greater lattice energy afforded by the more highly charged Ca²⁺ cation compared to the hypothetical Ca⁺ cation.

Calcium, strontium, barium, and radium are always considered to be alkaline earth metals; the lighter beryllium and magnesium, also in group 2 of the periodic table, are often included as well. Nevertheless, beryllium and magnesium are significantly different from the other members of the group in their physical and chemical behaviour: they behave more like aluminium and zinc respectively and have some of the weaker metallic character of the post-transition metals, which is why the traditional definition of the term "alkaline earth metal" excludes them. This classification is mostly obsolete in English-language sources, but is still used in other countries such as Japan. As a result, comparisons with strontium and barium are more germane to calcium chemistry than comparisons with magnesium.

Physical

Calcium metal melts at 842 °C and boils at 1494 °C; these values are higher than those for magnesium and strontium, the neighbouring group 2 metals. It crystallises in the face-centered cubic arrangement like strontium; above 450 °C, it changes to an anisotropic hexagonal close-packed arrangement like magnesium. Its density of 1.55 g/cm³ is the lowest in its group. Calcium is harder than lead but can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its very low density. While calcium is infeasible as a conductor for most terrestrial applications as it reacts quickly with atmospheric oxygen, its use as such in space has been considered.

Chemical

Structure of the polymeric [Ca(H₂O)₆]²⁺ center in hydrated calcium chloride, illustrating the high coordination number typical for calcium complexes.

 

The chemistry of calcium is that of a typical heavy alkaline earth metal. For example, calcium spontaneously reacts with water more quickly than magnesium and less quickly than strontium to produce calcium hydroxide and hydrogen gas. It also reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride. When finely divided, it spontaneously burns in air to produce the nitride. In bulk, calcium is less reactive: it quickly forms a hydration coating in moist air, but below 30% relative humidity it may be stored indefinitely at room temperature.

Besides the simple oxide CaO, the peroxide CaO₂ can be made by direct oxidation of calcium metal under a high pressure of oxygen, and there is some evidence for a yellow superoxide Ca(O₂)₂. Calcium hydroxide, Ca(OH)₂, is a strong base, though it is not as strong as the hydroxides of strontium, barium or the alkali metals. All four dihalides of calcium are known. Calcium carbonate (CaCO₃) and calcium sulfate (CaSO₄) are particularly abundant minerals. Like strontium and barium, as well as the alkali metals and the divalent lanthanides europium and ytterbium, calcium metal dissolves directly in liquid ammonia to give a dark blue solution.

Due to the large size of the Ca²⁺ ion, high coordination numbers are common, up to 24 in some intermetallic compounds such as CaZn₁₃. Calcium is readily complexed by oxygen chelates such as EDTA and polyphosphates, which are useful in analytic chemistry and removing calcium ions from hard water. In the absence of steric hindrance, smaller group 2 cations tend to form stronger complexes, but when large polydentate macrocycles are involved the trend is reversed.

Although calcium is in the same group as magnesium and organomagnesium compounds are very commonly used throughout chemistry, organocalcium compounds are not similarly widespread because they are more difficult to make and more reactive, although they have recently been investigated as possible catalysts. Organocalcium compounds tend to be more similar to organoytterbium compounds due to the similar ionic radii of Yb²⁺ (102 pm) and Ca²⁺ (100 pm). Most of these compounds can only be prepared at low temperatures; bulky ligands tend to favor stability. For example, calcium dicyclopentadienyl, Ca(C₅H₅)₂, must be made by directly reacting calcium metal with mercurocene or cyclopentadiene itself; replacing the C₅H₅ ligand with the bulkier C₅(CH₃)₅ ligand on the other hand increases the compound's solubility, volatility, and kinetic stability.

Isotopes

Natural calcium is a mixture of five stable isotopes (⁴⁰Ca, ⁴²Ca, ⁴³Ca, ⁴⁴Ca, and ⁴⁶Ca) and one isotope with a half-life so long that it can be considered stable for all practical purposes (⁴⁸Ca, with a half-life of about 4.3 × 10¹⁹ years). Calcium is the first (lightest) element to have six naturally occurring isotopes.

By far the most common isotope of calcium in nature is ⁴⁰Ca, which makes up 96.941% of all natural calcium. It is produced in the silicon-burning process from fusion of alpha particles and is the heaviest stable nuclide with equal proton and neutron numbers; its occurrence is also supplemented slowly by the decay of primordial ⁴⁰K. Adding another alpha particle would lead to unstable ⁴⁴Ti, which quickly decays via two successive electron captures to stable ⁴⁴Ca; this makes up 2.806% of all natural calcium and is the second-most common isotope. The other four natural isotopes, ⁴²Ca, ⁴³Ca, ⁴⁶Ca, and ⁴⁸Ca, are significantly rarer, each comprising less than 1% of all natural calcium. The four lighter isotopes are mainly products of the oxygen-burning and silicon-burning processes, leaving the two heavier ones to be produced via neutron-capturing processes. ⁴⁶Ca is mostly produced in a "hot" s-process, as its formation requires a rather high neutron flux to allow short-lived ⁴⁵Ca to capture a neutron. ⁴⁸Ca is produced by electron capture in the r-process in type Ia supernovae, where high neutron excess and low enough entropy ensures its survival.

⁴⁶Ca and ⁴⁸Ca are the first "classically stable" nuclides with a six-neutron or eight-neutron excess respectively. Although extremely neutron-rich for such a light element, ⁴⁸Ca is very stable because it is a doubly magic nucleus, having 20 protons and 28 neutrons arranged in closed shells. Its beta decay to ⁴⁸Sc is very hindered because of the gross mismatch of nuclear spin: ⁴⁸Ca has zero nuclear spin, being even–even, while ⁴⁸Sc has spin 6+, so the decay is forbidden by the conservation of angular momentum. While two excited states of ⁴⁸Sc are available for decay as well, they are also forbidden due to their high spins. As a result, when ⁴⁸Ca does decay, it does so by double beta decay to ⁴⁸Ti instead, being the lightest nuclide known to undergo double beta decay. The heavy isotope ⁴⁶Ca can also theoretically undergo double beta decay to ⁴⁶Ti as well, but this has never been observed; the lightest and most common isotope ⁴⁰Ca is also doubly magic and could undergo double electron capture to ⁴⁰Ar, but this has likewise never been observed. Calcium is the only element to have two primordial doubly magic isotopes. The experimental lower limits for the half-lives of ⁴⁰Ca and ⁴⁶Ca are 5.9 × 10²¹ years and 2.8 × 10¹⁵ years respectively.

Apart from the practically stable ⁴⁸Ca, the longest lived radioisotope of calcium is ⁴¹Ca. It decays by electron capture to stable ⁴¹K with a half-life of about a hundred thousand years. Its existence in the early Solar System as an extinct radionuclide has been inferred from excesses of ⁴¹K: traces of ⁴¹Ca also still exist today, as it is a cosmogenic nuclide, continuously reformed through neutron activation of natural ⁴⁰Ca. Many other calcium radioisotopes are known, ranging from ³⁴Ca to ⁵⁷Ca: they are all much shorter-lived than ⁴¹Ca, the most stable among them being ⁴⁵Ca (half-life 163 days) and ⁴⁷Ca (half-life 4.54 days). The isotopes lighter than ⁴²Ca usually undergo beta plus decay to isotopes of potassium, and those heavier than ⁴⁴Ca usually undergo beta minus decay to isotopes of scandium, although near the nuclear drip lines proton emission and neutron emission begin to be significant decay modes as well.

Like other elements, a variety of processes alter the relative abundance of calcium isotopes. The best studied of these processes is the mass-dependent fractionation of calcium isotopes that accompanies the precipitation of calcium minerals such as calcite, aragonite and apatite from solution. Lighter isotopes are preferentially incorporated into these minerals, leaving the surrounding solution enriched in heavier isotopes at a magnitude of roughly 0.025% per atomic mass unit (amu) at room temperature. Mass-dependent differences in calcium isotope composition are conventionally expressed by the ratio of two isotopes (usually ⁴⁴Ca/⁴⁰Ca) in a sample compared to the same ratio in a standard reference material. ⁴⁴Ca/⁴⁰Ca varies by about 1% among common earth materials.

History

One of the 'Ain Ghazal Statues, made from lime plaster

 

Calcium compounds were known for millennia, although their chemical makeup was not understood until the 17th century. Lime as a building material and as plaster for statues was used as far back as around 7000 BC. The first dated lime kiln dates back to 2500 BC and was found in Khafajah, Mesopotamia. At about the same time, dehydrated gypsum (CaSO₄·2H₂O) was being used in the Great Pyramid of Giza; this material would later be used for the plaster in the tomb of Tutankhamun. The climate of present-day Italy being warmer than that of Egypt, the ancient Romans instead used lime mortars made by heating limestone (CaCO₃); the name "calcium" itself derives from the Latin word calx "lime". Vitruvius noted that the lime that resulted was lighter than the original limestone, attributing this to the boiling of the water; in 1755, Joseph Black proved that this was due to the loss of carbon dioxide, which as a gas had not been recognised by the ancient Romans.

In 1787, Antoine Lavoisier suspected that lime might be an oxide of a fundamental chemical element. In his table of the elements, Lavoisier listed five "salifiable earths" (i.e., ores that could be made to react with acids to produce salts (salis = salt, in Latin): chaux (calcium oxide), magnésie (magnesia, magnesium oxide), baryte (barium sulfate), alumine (alumina, aluminium oxide), and silice (silica, silicon dioxide). About these "elements", Lavoisier speculated:

We are probably only acquainted as yet with a part of the metallic substances existing in nature, as all those which have a stronger affinity to oxygen than carbon possesses, are incapable, hitherto, of being reduced to a metallic state, and consequently, being only presented to our observation under the form of oxyds, are confounded with earths. It is extremely probable that barytes, which we have just now arranged with earths, is in this situation; for in many experiments it exhibits properties nearly approaching to those of metallic bodies. It is even possible that all the substances we call earths may be only metallic oxyds, irreducible by any hitherto known process.

Calcium, along with its congeners magnesium, strontium, and barium, was first isolated by Humphry Davy in 1808. Following the work of Jöns Jakob Berzelius and Magnus Martin af Pontin on electrolysis, Davy isolated calcium and magnesium by putting a mixture of the respective metal oxides with mercury(II) oxide on a platinum plate which was used as the anode, the cathode being a platinum wire partially submerged into mercury. Electrolysis then gave calcium–mercury and magnesium–mercury amalgams, and distilling off the mercury gave the metal. However, pure calcium cannot be prepared in bulk by this method and a workable commercial process for its production was not found until over a century later.

Occurrence and production

Travertine terraces in Pamukkale, Turkey

 

At 3%, calcium is the fifth most abundant element in the Earth's crust, and the third most abundant metal behind aluminium and iron. It is also the fourth most abundant element in the lunar highlands. Sedimentary calcium carbonate deposits pervade the Earth's surface as fossilized remains of past marine life; they occur in two forms, the rhombohedral calcite (more common) and the orthorhombic aragonite (forming in more temperate seas). Minerals of the first type include limestone, dolomite, marble, chalk, and iceland spar; aragonite beds make up the Bahamas, the Florida Keys, and the Red Sea basins. Corals, sea shells, and pearls are mostly made up of calcium carbonate. Among the other important minerals of calcium are gypsum (CaSO₄·2H₂O), anhydrite (CaSO₄), fluorite (CaF₂), and apatite ([Ca₅(PO₄)₃F]).

The major producers of calcium are China (about 10000 to 12000 tonnes per year), Russia (about 6000 to 8000 tonnes per year), and the United States (about 2000 to 4000 tonnes per year). Canada and France are also among the minor producers. In 2005, about 24000 tonnes of calcium were produced; about half of the world's extracted calcium is used by the United States, with about 80% of the output used each year. In Russia and China, Davy's method of electrolysis is still used, but is instead applied to molten calcium chloride. Since calcium is less reactive than strontium or barium, the oxide–nitride coating that results in air is stable and lathe machining and other standard metallurgical techniques are suitable for calcium. In the United States and Canada, calcium is instead produced by reducing lime with aluminium at high temperatures.

Geochemical cycling

Calcium cycling provides a link between tectonics, climate, and the carbon cycle. In the simplest terms, uplift of mountains exposes calcium-bearing rocks to chemical weathering and releases Ca²⁺ into surface water. These ions are transported to the ocean where they react with dissolved CO₂ to form limestone (CaCO
₃), which in turn settles to the sea floor where it is incorporated into new rocks. Dissolved CO₂, along with carbonate and bicarbonate ions, are termed "dissolved inorganic carbon" (DIC).

The actual reaction is more complicated and involves the bicarbonate ion (HCO⁻
₃) that forms when CO₂ reacts with water at seawater pH:

Ca²⁺ + 2HCO⁻
₃ → CaCO
_3(s) + CO
₂ + H
₂O

At seawater pH, most of the CO₂ is immediately converted back into HCO⁻
₃. The reaction results in a net transport of one molecule of CO₂ from the ocean/atmosphere into the lithosphere. The result is that each Ca²⁺ ion released by chemical weathering ultimately removes one CO₂ molecule from the surficial system (atmosphere, ocean, soils and living organisms), storing it in carbonate rocks where it is likely to stay for hundreds of millions of years. The weathering of calcium from rocks thus scrubs CO₂ from the ocean and atmosphere, exerting a strong long-term effect on climate.

Uses

The largest use of calcium is in steelmaking, due to its strong chemical affinity for oxygen and sulfur. Its oxides and sulfides, once formed, give liquid lime aluminate and sulfide inclusions in steel which float out; on treatment, these inclusions disperse throughout the steel and became small and spherical, improving castability, cleanliness and general mechanical properties. Calcium is also used in maintenance-free automotive batteries, in which the use of 0.1% calcium–lead alloys instead of the usual antimony–lead alloys leads to lower water loss and lower self-discharging. Due to the risk of expansion and cracking, aluminium is sometimes also incorporated into these alloys. These lead–calcium alloys are also used in casting, replacing lead–antimony alloys. Calcium is also used to strengthen aluminium alloys used for bearings, for the control of graphitic carbon in cast iron, and to remove bismuth impurities from lead. Calcium metal is found in some drain cleaners, where it functions to generate heat and calcium hydroxide that saponifies the fats and liquefies the proteins (for example, those in hair) that block drains. Besides metallurgy, the reactivity of calcium is exploited to remove nitrogen from high-purity argon gas and as a getter for oxygen and nitrogen. It is also used as a reducing agent in the production of chromium, zirconium, thorium, and uranium. It can also be used to store hydrogen gas, as it reacts with hydrogen to form solid calcium hydride, from which the hydrogen can easily be re-extracted.

Calcium isotope fractionation during mineral formation has led to several applications of calcium isotopes. In particular, the 1997 observation by Skulan and DePaolo that calcium minerals are isotopically lighter than the solutions from which the minerals precipitate is the basis of analogous applications in medicine and in paleooceanography. In animals with skeletons mineralized with calcium, the calcium isotopic composition of soft tissues reflects the relative rate of formation and dissolution of skeletal mineral. In humans, changes in the calcium isotopic composition of urine have been shown to be related to changes in bone mineral balance. When the rate of bone formation exceeds the rate of bone resorption, the ⁴⁴Ca/⁴⁰Ca ratio in soft tissue rises and vice versa. Because of this relationship, calcium isotopic measurements of urine or blood may be useful in the early detection of metabolic bone diseases like osteoporosis. A similar system exists in seawater, where ⁴⁴Ca/⁴⁰Ca tends to rise when the rate of removal of Ca²⁺ by mineral precipitation exceeds the input of new calcium into the ocean. In 1997, Skulan and DePaolo presented the first evidence of change in seawater ⁴⁴Ca/⁴⁰Ca over geologic time, along with a theoretical explanation of these changes. More recent papers have confirmed this observation, demonstrating that seawater Ca²⁺ concentration is not constant, and that the ocean is never in a "steady state" with respect to calcium input and output. This has important climatological implications, as the marine calcium cycle is closely tied to the carbon cycle.

Many calcium compounds are used in food, as pharmaceuticals, and in medicine, among others. For example, calcium and phosphorus are supplemented in foods through the addition of calcium lactate, calcium diphosphate, and tricalcium phosphate. The last is also used as a polishing agent in toothpaste and in antacids. Calcium lactobionate is a white powder that is used as a suspending agent for pharmaceuticals. In baking, calcium monophosphate is used as a leavening agent. Calcium sulfite is used as a bleach in papermaking and as a disinfectant, calcium silicate is used as a reinforcing agent in rubber, and calcium acetate is a component of liming rosin and is used to make metallic soaps and synthetic resins.

Biological and pathological role

Age-adjusted daily calcium recommendations (from U.S. Institute of Medicine RDAs)

Age	Calcium (mg/day)
1–3 years	700
4–8 years	1000
9–18 years	1300
19–50 years	1000
>51 years	1000
Pregnancy	1000
Lactation	1000

Global dietary calcium intake among adults (mg/day).

  <400 span="">

  400-500

  500-600

  600-700

  700-800

  800-900

  900-1000

  >1000

Calcium is an essential element needed in large quantities. The Ca²⁺ ion acts as an electrolyte and is vital to the health of the muscular, circulatory, and digestive systems; is indispensable to the building of bone; and supports synthesis and function of blood cells. For example, it regulates the contraction of muscles, nerve conduction, and the clotting of blood. As a result, intra- and extracellular calcium levels are tightly regulated by the body. Calcium can play this role because the Ca²⁺ ion forms stable coordination complexes with many organic compounds, especially proteins; it also forms compounds with a wide range of solubilities, enabling the formation of skeletons.

Calcium ions may be complexed by proteins through binding the carboxyl groups of glutamic acid or aspartic acid residues; through interacting with phosphorylated serine, tyrosine, or threonine residues; or by being chelated by γ-carboxylated amino acid residues. Trypsin, a digestive enzyme, uses the first method; osteocalcin, a bone matrix protein, uses the third. Some other bone matrix proteins such as osteopontin and bone sialoprotein use both the first and the second. Direct activation of enzymes by binding calcium is common; some other enzymes are activated by noncovalent association with direct calcium-binding enzymes. Calcium also binds to the phospholipid layer of the cell membrane, anchoring proteins associated with the cell surface. As an example of the wide range of solubility of calcium compounds, monocalcium phosphate is very soluble in water, 85% of extracellular calcium is as dicalcium phosphate with a solubility of 2.0 mM and the hydroxyapatite of bones in an organic matrix is tricalcium phosphate at 100 µM.

About three-quarters of dietary calcium is from dairy products and grains, the rest being accounted for by vegetables, protein-rich foods, fruits, sugar, fats, and oil. Calcium supplementation is controversial, as the bioavailability of calcium is strongly dependent on the solubility of the salt involved: calcium citrate, malate, and lactate are highly bioavailable while the oxalate is much less so. The intestine absorbs about one-third of calcium eaten as the free ion, and plasma calcium level is then regulated by the kidneys. Parathyroid hormone and vitamin D promote the formation of bone by allowing and enhancing the deposition of calcium ions there, allowing rapid bone turnover without affecting bone mass or mineral content. When plasma calcium levels fall, cell surface receptors are activated and the secretion of parathyroid hormone occurs; it then proceeds to stimulate the entry of calcium into the plasma pool by taking it from targeted kidney, gut, and bone cells, with the bone-forming action of parathyroid hormone being antagonised by calcitonin, whose secretion increases with increasing plasma calcium levels.

Excess intake of calcium may cause hypercalcaemia. However, because calcium is absorbed rather inefficiently by the intestines, high serum calcium is more likely caused by excessive secretion of parathyroid hormone (PTH) or possibly by excessive intake of vitamin D, both which facilitate calcium absorption. It may also be due to bone destruction that occurs when tumours metastasize within bone. All these conditions result in excess calcium salts being deposited in the heart, blood vessels, or kidneys. Symptoms include anorexia, nausea, vomiting, memory loss, confusion, muscle weakness, increased urination, dehydration, and metabolic bone disease. Chronic hypercalcaemia typically leads to calcification of soft tissue and its serious consequences: for example, calcification can cause loss of elasticity of vascular walls and disruption of laminar blood flow—and thence to plaque rupture and thrombosis. Conversely, inadequate calcium or vitamin D intakes may result in hypocalcaemia, often caused also by inadequate secretion of parathyroid hormone or defective PTH receptors in cells. Symptoms include neuromuscular excitability, which potentially causes tetany and disruption of conductivity in cardiac tissue.

As calcium is heavily involved in bone manufacture, many bone diseases can be traced to problems with the organic matrix or the hydroxyapatite in molecular structure or organisation. For example, osteoporosis is a reduction in mineral content of bone per unit volume, and can be treated by supplementation of calcium, vitamin D, and biphosphates. Calcium supplements may benefit the serum lipids in women who have passed menopause as well as older men; in post-menopausal women calcium supplementation also appears to be inversely correlated with cardiovascular disease. Inadequate amounts of calcium, vitamin D, or phosphates can lead to the softening of bones, known as osteomalacia.

Safety

Metallic calcium

Calcium

Hazards
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H261
GHS precautionary statements	P231+232, P422
NFPA 704	3 0 1 W

Because calcium reacts exothermically with water and acids, calcium metal coming into contact with bodily moisture results in severe corrosive irritation. When swallowed, calcium metal has the same effect on the mouth, oesophagus, and stomach, and can be fatal. However, long-term exposure is not known to have distinct adverse effects.

Calcium in food

Because of concerns for long-term adverse side effects, including calcification of arteries and kidney stones, both the U.S. Institute of Medicine (IOM) and the European Food Safety Authority (EFSA) set Tolerable Upper Intake Levels (ULs) for combined dietary and supplemental calcium. From the IOM, people of ages 9–18 years are not to exceed 3 g/day combined intake; for ages 19–50, not to exceed 2.5 g/day; for ages 51 and older, not to exceed 2 g/day. The EFSA set the UL for all adults at 2.5 g/day, but decided the information for children and adolescents was not sufficient to determine ULs.

Liberal Christianity

From Wikipedia, the free encyclopedia

Liberal Christianity, also known as liberal theology, covers diverse philosophically and biblically informed religious movements and ideas within Christianity from the late 18th century onward. Liberal does not refer to progressive Christianity or to political liberalism but to the philosophical and religious thought that developed and grew as a consequence of the Enlightenment.

 

Liberal Christianity, broadly speaking, is a method of biblical hermeneutics, an undogmatic method of understanding God through the use of scripture by applying the same modern hermeneutics used to understand any ancient writings, symbols and scriptures. Liberal Christianity did not originate as a belief structure, and as such was not dependent upon any Church dogma or creed. Liberal Christianity from the start embraced the methodologies of Enlightenment science, including empirical evidence and the use of reason, as the basis for interpreting the Bible, life, faith and theology.

The word liberal in liberal Christianity originally denoted a characteristic willingness to interpret scripture according to modern philosophic perspectives (hence the parallel term modernism) and modern scientific assumptions, while attempting to achieve the Enlightenment ideal of objective point of view, without preconceived notions of the authority of scripture or the correctness of Church dogma. Liberal Christians may hold certain beliefs in common with Roman Catholicism, Orthodox Christianity, or even fundamentalist Protestantism.

Liberal Protestantism

Liberal Protestantism developed in the 19th century out of a need to adapt Christianity to a modern intellectual context. With the acceptance of Charles Darwin's theory of natural selection, some traditional Christian beliefs, such as parts of the Genesis creation narrative, became difficult to defend. Unable to ground faith exclusively in an appeal to scripture or the person of Jesus Christ, liberals, according to theologian and intellectual historian Alister McGrath, "sought to anchor that faith in common human experience, and interpret it in ways that made sense within the modern worldview." Beginning in Germany, liberal theology was influenced by several strands of thought, including the Enlightenment's high view of human reason and Pietism's emphasis on religious experience and interdenominational tolerance.

The sources of religious authority recognized by liberal Protestants differed from traditional Protestants. Traditional Protestants understood the Bible to be uniquely authoritative (sola scriptura); all doctrine, teaching and the church itself derive authority from it. A traditional Protestant could therefore affirm that "what Scripture says, God says." Liberals, however, seek to understand the Bible through modern biblical criticism, such as historical criticism, that began to be used in the late 1700s to ask if biblical accounts were based on older texts or whether the Gospels recorded the actual words of Jesus. The use of these methods of biblical interpretation led liberals to conclude that "none of the New Testament writings can be said to be apostolic in the sense in which it has been traditionally held to be so". This conclusion made sola scriptura untenable. In its place, liberals identified the historical Jesus as the "real canon of the Christian church".

The two groups also disagreed on the role of experience in confirming truth claims. Traditional Protestants believed scripture and revelation always confirmed human experience and reason. For liberal Protestants , there were two ultimate sources of religious authority: the Christian experience of God as revealed in Jesus Christ and universal human experience. In other words, only an appeal to common human reason and experience could confirm the truth claims of Christianity.

Liberals abandoned or reinterpreted traditional doctrines in light of recent knowledge. For example, the traditional doctrine of original sin was rejected for being derived from Augustine of Hippo, whose views on the New Testament were believed to have been distorted by his involvement with Manichaeism. Christology was also reinterpreted. Liberals stressed Christ's humanity, and his divinity became "an affirmation of Jesus exemplifying qualities which humanity as a whole could hope to emulate". Liberal Christians sought to elevate Jesus' humane teachings as a standard for a world civilization freed from cultic traditions and traces of "pagan" belief in the supernatural.

As a result, liberal Christians placed less emphasis on miraculous events associated with the life of Jesus than on his teachings. The effort to remove "superstitious" elements from Christian faith dates to intellectually reforming Renaissance Christians such as Erasmus (who compiled the first modern Greek New Testament) in the late 15th and early-to-mid 16th centuries, and, later, the natural-religion view of the Deists, which disavowed any revealed religion or interaction between the Creator and the creation, in the 17–18th centuries. The debate over whether a belief in miracles was mere superstition or essential to accepting the divinity of Christ constituted a crisis within the 19th-century church, for which theological compromises were sought. Many liberals prefer to read Jesus' miracles as metaphorical narratives for understanding the power of God. Not all theologians with liberal inclinations reject the possibility of miracles, but many reject the polemicism that denial or affirmation entails.

Nineteenth-century liberalism had an optimism about the future in which humanity would continue to achieve greater progress. This optimistic view of history was sometimes interpreted as building the kingdom of God in the world.

Theologians

Reformed theologian Friedrich Schleiermacher is often considered the father of liberal Protestantism. In response to Romanticism's disillusionment with Enlightenment rationalism, Schleiermacher argued that God could only be experienced through feeling, not reason. In Schleiermacher's theology, religion is a feeling of absolute dependence on God. Humanity is conscious of its own sin and its need of redemption, which can only be accomplished by Jesus Christ. For Schleirmacher, faith is experienced within a faith community, never in isolation. This meant that theology always reflects a particular religious context, which has opened Schleirmacher to charges of relativism.

Albrecht Ritschl disagreed with Schleiermacher's emphasis on feeling. He thought that religious belief should be based on history, specifically the historical events of the New Testament. When studied as history without regard to miraculous events, Ritschl believed the New Testament affirmed Jesus' divine mission. He rejected doctrines such as the virgin birth of Jesus and the Trinity. The Christian life for Ritschl was devoted to ethical activity and development, so he understood doctrines to be value judgments rather than assertions of facts. Influenced by the philosophy of Emmanuel Kant, Ritschl viewed "religion as the triumph of the spirit (or moral agent) over humanity’s natural origins and environment." Ritschl's ideas would be taken up by others, and Ritschlianism would remain an important theological school within German Protestantism until World War I. Prominent followers of Ritschl include Wilhelm Herrmann, Julius Kaftan and Adolf von Harnack.

Liberal Catholicism

Catholic forms of theological liberalism have existed since the 19th century in England, France and Italy. In the late 19th and early 20th centuries, a liberal theological movement developed within the Catholic Church known as Catholic modernism. Like liberal Protestantism, Catholic modernism was an attempt to bring Catholicism in line with the Enlightenment. Modernist theologians approved of radical biblical criticism and were willing to question traditional Christian doctrines, especially Christology. They also emphasized the ethical aspects of Christianity over its theological ones. Important modernist writers include Alfred Loisy and George Tyrrell. Modernism was condemned as heretical by the leadership of the Catholic Church.

Papal condemnation of modernism and Americanism slowed the development of a liberal Catholic tradition in the United States. Since the Second Vatican Council, however, liberal theology has experienced a resurgence. Liberal Catholic theologians include David Tracy and Francis Schussler Fiorenza.

Influence in the United States

Liberal Christianity was most influential with Mainline Protestant churches in the early 20th century, when proponents believed the changes it would bring would be the future of the Christian church. Its greatest and most influential manifestation was the Christian Social Gospel, whose most influential spokesman was the American Baptist Walter Rauschenbusch. Rauschenbusch identified four institutionalized spiritual evils in American culture (which he identified as traits of "supra-personal entities", organizations capable of having moral agency): these were individualism, capitalism, nationalism and militarism.

Other subsequent theological movements within the U.S. Protestant mainline included political liberation theology, philosophical forms of postmodern Christianity, and such diverse theological influences as Christian existentialism (originating with Søren Kierkegaard and including other theologians and scholars such as Rudolf Bultmann and Paul Tillich ) and even conservative movements such as neo-evangelicalism, neo-orthodoxy, and paleo-orthodoxy. Dean M. Kelley, a liberal sociologist, was commissioned in the early 1970s to study the problem, and he identified a potential reason for the decline of the liberal churches: what was seen by some as excessive politicization of the Gospel, and especially their apparent tying of the Gospel with Left-Democrat/progressive political causes.

The 1990s and 2000s saw a resurgence of non-doctrinal, theological work on biblical exegesis and theology, exemplified by figures such as Marcus Borg, John Dominic Crossan, John Shelby Spong, Karen Armstrong and Scotty McLennan.

Theologians and authors

Anglican and Protestant

• Friedrich Daniel Ernst Schleiermacher (1768–1834), often called the "father of liberal theology," he claimed that religious experience was introspective, and that the most true understanding of God consisted of "a sense of absolute dependence".
• Charles Augustus Briggs (1841–1913), early advocate of higher criticism of the Bible.
• Henry Ward Beecher (1813–1887), American preacher who left behind the Calvinist orthodoxy of his famous father, the Reverend Lyman Beecher, to instead preach the Social Gospel of liberal Christianity.
• Adolf von Harnack, (1851–1930), German theologian and church historian, promoted the Social Gospel; wrote a seminal work of historical theology called Lehrbuch der Dogmengeschichte (History of Dogma).
• Charles Fillmore (1854–1948), Christian mystic influenced by Emerson; co-founder, with his wife, Myrtle Fillmore, of the Unity Church.
• Walter Rauschenbusch (1861–1918) American Baptist, author of "A Theology for the Social Gospel", which gave the movement its definitive theological definition.
• Harry Emerson Fosdick (1878–1969), a Northern Baptist, founding pastor of New York's Riverside Church in 1922.
• Rudolf Bultmann (1884–1976), German biblical scholar, liberal Christian theologian until 1924. Bultmann was more of an existentialist than a "liberal", as his defense of Jesus' healings in his "History of Synoptic Tradition" makes clear.
• Paul Tillich (1886–1965), seminal figure in liberal Christianity; synthesized liberal Protestant theology with existentialist philosophy, but later came to be counted among the "neo-orthodox".
• Leslie Weatherhead (1893–1976), English preacher and author of The Will of God and The Christian Agnostic
• James Pike (1913–1969), Episcopal Bishop, Diocese of California 1958-66. Early television preacher as Dean of St. John the Divine Cathedral in New York City; social gospel advocate and civil rights supporter; author of "If This Be Heresy" and "The Other Side;" in later life studied Christian origins and spiritualism.
• Lloyd Geering (1918–), New Zealand liberal theologian.
• Paul Moore, Jr. (1919–2003), 13th Episcopal Bishop, New York Diocese
• John A.T. Robinson (1919–1983), Anglican Bishop of Woolwich, author of Honest to God; later dedicated himself to demonstrating very early authorship of the New Testament writings, publishing his findings in Redating the New Testament.
• John Hick (1922–2012) British philosopher of religion and liberal theologian, noted for his rejection of the Incarnation and advocacy of latitudinarianism and religious pluralism or non-exclusivism, as explained in his influential work, The Myth of God Incarnate.
• William Sloane Coffin (1924–2006), Senior Minister at the Riverside Church in New York City, and President of SANE/Freeze (now Peace Action).
• Christopher Morse (1935–) Professor Emeritus of Systematic Theology, Union Theological Seminary, noted for his theology of faithful disbelief.
• John Shelby Spong (1931–), Episcopalian bishop and very prolific author of books such as A New Christianity for a New World, in which he wrote of his rejection of historical religious and Christian beliefs such as Theism (a traditional conception of God as an existent being), the afterlife, miracles, and the Resurrection.
• Richard Holloway (1933–), Bishop of Edinburgh 1986-2000.
• Rubem Alves, (b. 1938) Brazilian, ex-Presbyterian, former minister, retired professor from UNICAMP, seminal figure in the liberation theology movement.
• Matthew Fox (b. 1940), former Roman Catholic priest of the Order of Preachers; currently an American Episcopalian priest and theologian, noted for his synthesis of liberal Christian theology with New Age concepts in his ideas of "creation spirituality", "original blessing", and seminal work on the "Cosmic Christ"; founder of Creation Spirituality.
• Marcus Borg (1942–2015) American Biblical scholar, prolific author, fellow of the Jesus Seminar.
• Michael Dowd (b. 1958) Religious Naturalist theologian, evidential evangelist, and promoter of Big History and the Epic of Evolution.
• Douglas Ottati, Presbyterian theologian and author, former professor at Union-PSCE, current professor at Davidson College.

Roman Catholic

• Thomas Berry (1914–2009), American Passionist priest, cultural historian, geologian, and cosmologist.
• Gustavo Gutiérrez Merino (born 8 June 1928) is a Peruvian philosopher, theologian, and Dominican priest regarded as one of the founders of liberation theology. He currently holds the John Cardinal O'Hara Professorship of Theology at the University of Notre Dame, and has previously been a professor at the Pontifical Catholic University of Peru and a visiting professor at many major universities in North America and Europe.
• Hans Küng, (b. 1928) Swiss theologian. Had his license to teach Catholic theology revoked in 1979 because of his vocal rejection of the doctrine of the infallibility of the Pope, but remains a priest in good standing.
• John Dominic Crossan, (b. 1934) ex-Catholic and former priest, New Testament scholar, co-founder of the critical liberal Jesus Seminar.
• Joan Chittister, (b. 1936) Benedictine lecturer and social psychologist.
• Elisabeth Schüssler Fiorenza (born 1938) German feminist theologian and Professor at Harvard Divinity School
• Leonardo Boff, (b. 1938) Brazilian, ex-Franciscan and former priest, seminal author of the liberation theology movement, condemned by the Church; his works were condemned in 1985, and almost again condemned in 1992, which led him to leave the Franciscan order and the priestly ministry.

Other

• William Ellery Channing (1780–1842), Unitarian liberal theologian in the United States, who rejected the Trinity and the strength of scriptural authority, in favor of purely rationalistic "natural religion".
• Scotty McLennan (b. 1948) Unitarian Universalist minister, Stanford University professor and author.