Calcium is the chemical element with atomic number 20, symbol Ca

Crystals of calcium

Calcium is the chemical element with atomic number 20, symbol Ca

It is a fairly hard gray-white alkaline earth metal. Calcium does not exist as a pure body in nature. It is the fifth most abundant element in the earth’s crust (over 3%). It is vital for many species: formation of bones, teeth and shells (it makes up 1 to 2% of the weight of the human body of an adult). Calcium also plays a very important role in cellular physiology, while being a cellular poison beyond a certain dose.

Physical applications of calcium metal

  • Reducing agent in the extraction of other metals such as uranium, zirconium, and thorium;
  • deoxidizer, desulfurizer or decarburizer for various ferrous and non-ferrous alloys;
  • used, sometimes in combination with magnesium, to remove bismuth from lead (deismuthage);
  • alloying agent used in the production of alloys of aluminum, beryllium, copper, lead and magnesium.


Metallic calcium is used as a reducing agent in metallurgy for the production of metals such as thorium, vanadium, zirconium, yttrium and other rare earth metals , as a reducing agent in steel and aluminum production, as an alloy additive in aluminum, beryllium, copper, lead – and magnesium alloys and as a starting material for the production of calcium hydride.

The technical use of calcium takes place predominantly in bound form.

Limestone (mainly calcium carbonate, CaCO3) and dolomite (CaMg (CO3 ) 2 ) are two of the most important raw materials in today’s industry:

  • Slagging agent in steel production . The consumption is 0.5 tons of limestone per ton of steel
  • Raw material for the production of quick lime.
  • Chalk as a filler for plastics, for example PVC . The aim is to improve stiffness and impact strength, as well as to reduce shrinkage. The also greatly increased thermal conductivity allows higher work cycles during extrusion.
  • Fine-grain calcium carbonate is used as a filler in high-quality, wood-free paper.
  • Finely ground lime or dolomite is used as fertilizer lime in agriculture and forestry or as fodder lime in animal husbandry.

Because of its functions in organisms, calcium is also used as a drug.

Here are some of the benefits of calcium for humans

Activates nerves
Blood circulation
Flex muscles
Normalizes blood pressure
Balance the acidity of the blood
Maintain body fluid balance
Prevent osteoporosis (bone loss)
Prevent heart disease
Reducing the risk of colon cancer
Overcoming cramps, back pain, hemorrhoids, and rheumatism
Overcoming complaints during menstruation and menopause
Minimizes bone loss during pregnancy and breastfeeding
Helps mineralization of teeth and prevents tooth root bleeding
Overcoming dry and cracked skin on the feet and hands
Restores decreased / weakened sex drive
Overcoming diabetes (activates the pancreas)
After the age of 20 years, the human body will begin to experience calcium deficiency as much as 1% per year. And after the age of 50 years, the amount of calcium content in the body will shrink by 30%. Losses will reach 50% when you reach the age of 70 years and thereafter experiencing calcium deficiency problems.

The initial symptoms of calcium deficiency include lethargy, profuse sweating, restlessness, shortness of breath, decreased endurance, lack of appetite, constipation, loose stools, insomnia, cramps, and so on.
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Recommended Calcium Intakes

Age-adjusted daily calcium recommendations (from U.S. Institute of Medicine RDAs)
AgeCalcium (mg/day)
1–3 years700
4–8 years1000
9–18 years1300
19–50 years1000
>51 years1000

The FAO (Food and Agriculture Organization) nutritional recommendations are based on the relationships between calcium intake and calcium absorption and excretion, determined by an analysis of existing studies. Balance, according to the FAO, is reached with a daily intake of 520 mg taking into account the incompressible faecal losses, which rise to 840 mg taking into account the urinary losses and those related to desquamation, and to 1,100 mg when the Menopause-related losses are included.

Taking into account dietary intake of animal protein has a major effect on nutritional calcium requirements, the two being positively correlated14. It also helps to bring the recommended calcium intakes closer to the actual calcium intakes observed in a large part of the populations worldwide. Regarding sodium, if the salt intake in the diet were reduced, the calcium requirement could decrease to a level as low as 450 mg / d. Better attention to vitamin D levels (through sufficient exposure to the sun or through sufficient intake) could further reduce nutritional calcium requirements.

The recommended nutritional intake is finally 900 mg per day in adults who consume a Western diet. A WHO (World Health Organization) study shows that DRI (Dietary Reference Intake) vary significantly between developed countries. At the same time, the recommended daily allowance is 800 mg per day (for an adult woman).

According to the WHO and FAO, a much lower calcium requirement (500 mg / day) is observed in people with a much more vegetarian diet, who are sufficiently exposed to the sun (vitamin D) and who exercise non-sedentary. Indeed, the ingestion of sulfur amino acids (such as methionine) in large quantities would increase the loss of calcium in the urine. These sulfur amino acids are found in large quantities in meats, fish, eggs, cold cuts.

Consequences of excess calcium

A study of a population cohort in Sweden found higher mortality for women ingesting more than 1,400 mg of calcium per day, especially in supplement form. In addition, several studies establish a correlation between a high intake of calcium and a high incidence of prostate cancer.

Food sources

The United States Department of Agriculture (USDA) web site has a very complete searchable table of calcium content (in milligrams) in foods, per common measures such as per 100 grams or per a normal serving.

Food, calcium per 100 grams
Food, calcium per 100 grams
parmesan (cheese) = 1140 mg
milk powder = 909 mg
goat hard cheese = 895 mg
Cheddar cheese = 720 mg
tahini paste = 427 mg
molasses = 273 mg
almonds = 234 mg
collard greens = 232 mg
kale = 150 mg
goat milk = 134 mg
sesame seeds (unhulled) = 125 mg
nonfat cow milk = 122 mg
plain whole-milk yogurt = 121 mg
Food, calcium per 100 grams
Food, calcium per 100 grams
hazelnuts = 114 mg
tofu, soft = 114 mg
beet greens = 114 mg
spinach = 99 mg
ricotta (skimmed milk cheese) = 90 mg
lentils = 79 mg
chickpeas = 53 mg
eggs, boiled = 50 mg
orange = 40 mg
human milk = 33 mg
rice, white, long-grain = 19 mg
beef = 12 mg
cod = 11 mg
Measurement in blood

The amount of calcium in blood (more specifically, in blood plasma) can be measured as total calcium, which includes both protein-bound and free calcium. In contrast, ionized calcium is a measure of free calcium. An abnormally high level of calcium in plasma is termed hypercalcemia and an abnormally low level is termed hypocalcemia, with “abnormal” generally referring to levels outside the reference range.

Reference ranges for blood tests for calcium
TargetLower limitUpper limitUnit
Ionized calcium1.03, 1.101.23, 1.30mmol/L
4.1, 4.44.9, 5.2mg/dL
Total calcium2.1, 2.22.5, 2.6, 2.8mmol/L
8.4, 8.510.2, 10.5mg/dL

The main methods to measure serum calcium are:

  • O-Cresolphalein Complexone Method; A disadvantage of this method is that the volatile nature of the 2-amino-2-methyl-1-propanol used in this method makes it necessary to calibrate the method every few hours in a clinical laboratory setup.
  • Arsenazo III Method; This method is more robust, but the arsenic in the reagent is a health hazard.

The total amount of Ca2+ present in a tissue may be measured using Atomic absorption spectroscopy, in which the tissue is vaporized and combusted. To measure Ca2+ concentration or spatial distribution within the cell cytoplasm in vivo or in vitro, a range of fluorescent reporters may be used. These include cell permeable, calcium-binding fluorescent dyes such as Fura-2 or genetically engineered variant of green fluorescent protein (GFP) named Cameleon.

Corrected calcium

As access to an ionized calcium is not always available a corrected calcium may be used instead. To calculate a corrected calcium in mmol/L one takes the total calcium in mmol/L and adds it to ((40 minus the serum albumin in g/L) multiplied by 0.02). There is, however, controversy around the usefulness of corrected calcium as it may be no better than total calcium. It may be more useful to correct total calcium for both albumin and the anion gap.

Calcium in the periodic table

Atomic number (Z)20
Groupgroup 2 (alkaline earth metals)
Periodperiod 4
Block  s-block
Electron configuration[Ar] 4s2
Electrons per shell2, 8, 8, 2

Physical properties

Physical properties
Phase at STPsolid
Melting point1115 K ​(842 °C, ​1548 °F)
Boiling point1757 K ​(1484 °C, ​2703 °F)
Density (near r.t.)1.55 g/cm3
when liquid (at m.p.)1.378 g/cm3
Heat of fusion8.54 kJ/mol
Heat of vaporisation154.7 kJ/mol
Molar heat capacity25.929 J/(mol·K)

Vapour pressure

P (Pa)1101001 k10 k100 k
at T (K)8649561071122714431755

Atomic properties

Atomic properties
Oxidation states+1, +2 (a strongly basic oxide)
ElectronegativityPauling scale: 1.00
Ionisation energies
  • 1st: 589.8 kJ/mol
  • 2nd: 1145.4 kJ/mol
  • 3rd: 4912.4 kJ/mol
  • (more)
Atomic radiusempirical: 197 pm
Covalent radius176±10 pm
Van der Waals radius231 pm

Other properties

Other properties
Natural occurrenceprimordial
Crystal structure​face-centred cubic (fcc)
Speed of sound thin rod3810 m/s (at 20 °C)
Thermal expansion22.3 µm/(m·K) (at 25 °C)
Thermal conductivity201 W/(m·K)
Electrical resistivity33.6 nΩ·m (at 20 °C)
Magnetic orderingdiamagnetic
Magnetic susceptibility+40.0·10−6 cm3/mol[4]
Young’s modulus20 GPa
Shear modulus7.4 GPa
Bulk modulus17 GPa
Poisson ratio0.31
Mohs hardness1.75
Brinell hardness170–416 MPa
CAS Number7440-70-2


Discovery and first isolationHumphry Davy (1808)

The name “calcium” is derived from the Latin word calx . This is how the Romans called lime, limestone, chalk and mortar made from lime ( building lime ).

Elemental calcium was first obtained by Humphry Davy in 1808 by evaporating the mercury from electrolytically obtained calcium amalgam.

Main isotopes of calcium

Main isotopes of calcium
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
41Catrace9.94×104 yε41K
45Casyn162.6 dβ45Sc
47Casyn4.5 dβ47Sc
48Ca0.187%6.4×1019 yββ48Ti

Periodic Table of Elements | Complete List of Chemical Elements by Group, Name, Symbol, Color and Type

Periodic table elements
Periodic Table of Elements | Complete List of Chemical Elements by Group, Name, Symbol, Color and Type

Sources: Royal Society of Chemistry

Photo credit: Wikimedia Commons

Photo explanations: Crystals of pure 99,99% Calcium. Crystals of calcium stored in a protective atmosphere.

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