Calcium (Ca)

Calcium is a chemical element with an atomic number of 20 in the periodic table of elements. It’s the fifth most plentiful metal found in Earth’s crust and the most abundant mineral in the human body.

Being a member of the alkali earth metals family of periodic table elements, this chemical substance has two valence electrons. In this way, calcium easily forms numerous compounds.

Chemical and Physical Properties of Calcium

The symbol in the periodic table of elementsCa
Atomic number20
Atomic weight (mass)40.078 g.mol-1
Group numberGroup 2 (IIa)
ColorA dull gray, silver metal with a pale yellow tint
Physical stateA lightweight metal at room temperature
Half-lifeFrom a few days to 100,000 years
Electronegativity according to Pauling1
Melting point842 °C (1,548 °F)
Boiling point1,484 °C (2,703 °F)
Van der Waals radius0.197 nm
Ionic radius0.099 nm
Most characteristic isotopeCalcium-40
Electronic shell[Ar] 4s2
The energy of the first ionization589.6 kJ.mol-1
The energy of the second ionization1145 kJ.mol-1
Discovery dateIn 1808 by Sir Humphry Davy

This alkaline earth metal is labeled with the symbol Ca in the periodic table of elements. It’s a trimorphic element, meaning it occurs in three distinct forms. It has 20 protons and 20 electrons, an atomic weight of 40.078 g.mol -1, electron configuration 1s22s22p63s23p64s2, and oxidation state of +2. 

Calcium shares both the chemical and physical properties with the members of the group it belongs to – the elements strontium, barium, and radium. With a cubic crystal structure, its boiling point occurs at 1,484 °C (2,703 °F), while the melting point of calcium is achieved at 842 °C (1,548 °F).

Furthermore, the fact sheet of this member of the alkali earth metals family of elements in the periodic table also contains the following values: an electronegativity of 1.0 according to Pauling, and an atomic radius according to van der Waals is 0.197 nm. 

Calcium is highly reactive with water – it occurs as Ca2+ (aq), CaOH+ (aq), Ca(OH)2 (aq), or as CaSO4. Due to its buffering qualities, calcium is often used as a pH stabilizer in drinking water which makes it more tasteful. 

Water-solving calcium hydroxide is formed with the following reaction:

Ca (s) + 2H2O (g) -> Ca(OH)2 (aq) + H2 (g)

How Was Calcium Discovered?

The Egyptian blue, or calcium copper silicate (CaCuSi4O10) also known as cuprorivaite, has been used since ancient times (approximately 5000 years ago) as a coloring pigment with vivid blue color. The Latin name for this first synthetically produced pigment was ‘caeruleum’, meaning ‘color of the sky’.

Since the Egyptians considered the blue color as the color of the heavens and the Universe, they worshipped the lapis lazuli – a naturally found mineral with an intensive blue color. However, this semi-precious stone was perceived as a luxury item even in ancient times. Therefore, the people from this ancient civilization succeeded in manufacturing its alternative, called accordingly – the ‘Egyptian blue’. 

The first evidence of this form of calcium dates from the time of the last pharaoh of the First Egyptian Dynasty, Sekhen. Egyptians were mainly using the calcium copper silicate to make the ceramic glaze known as the ‘Egyptian faience’.

Due to its beautiful color and properties that the ancient Egyptians assigned to this gemstone, it quickly found its way among the people of the Meditteranean. The monumental Parthenon in Athens and some paintings found in Pompeii evidence of the use of this mineral by the ancient Greeks and Romans, respectively.   

The ancient civilizations have also used calcium oxide (CaO), i.e. the lime, as a building material. Prior to the use, they were heating the calcium compound in order to obtain mortar. 

The father of modern chemistry, Antoine-Laurent de Lavoisier (Antoine Lavoisier) regarded calcium as an unknown chemical element oxide and classified it as an earth element since he believed that it cannot be further reduced.  

In 1808, the British chemist Sir Humphrey Davy attempted to distill mercury from lime and a mercuric oxide compound with the method of electrolysis. The experiment he conducted resulted in a silvery metal that’s softer than aluminum, which entered the periodic table of elements in the second group of alkali earth elements. It was the pure form of calcium (Ca). 

How Did Calcium Get Its Name?

The Latin word ‘calx’, denoting lime, was used to label this chemical element of the alkali earth metal family of periodic table elements. 

Where Can You Find Calcium?

Accumulated in a quantity of 3.64 percent in the Earth’s crust, calcium can be found as a calcium carbonate compound (CO3) that occurs in limestone (CaCo3), fluorite (CaF2), chalk, eggshells, gypsum (CaSO4·2H2O), pearls, apatite [Ca₅(PO₄)₃], the shells of the marine animals, corals, stalactites, stalagmites, marble, and dolomite. 

Calcium also comprises about 8 percent of the Moon’s crust, and naturally occurs in the waters by dissolving from calcite rocks. Despite the fact that this chemical substance cannot be easily found in its elemental form, it does create an abundance of compounds that can be traced in rock-forming minerals such as feldspars and zeolites.

Calcium and Human Health 

Calcium is one of the most important trace elements since it is the main substance of which our bones and teeth are made of. In fact, it’s found in almost all life-forms on Earth. Since our skeletal system and teeth are made of over 99% of this chemical substance, calcium makes for one of the main components required for a healthy bone structure and strong teeth in the form of calcium hydroxyl phosphate. 

This mineral is also very important for the proper function of the heart, muscles, and nervous system. It supports the proper functioning of the cellular mechanisms and the division of neuronal cells. In addition, this essential nutrient supports the relay of sensory information to the dedicated brain areas, the secretion of hormones, etc. 

Which Foods Are Rich in Calcium??

Calcium-rich foods, such as dairy foods (cheeses, milk drinks, milk products) and broccoli, are recommended to be included in the daily diet for healthier teeth and bones, as well as for the overall wellbeing. Calcium is especially important for children, pregnant women, vegans, as well as older people, due to the increased or decreased calcium absorption, respectively. 

Dairy products, salmon, kale, Chinese cabbage, bok choy, collard greens, cheddar cheese, cottage cheese, fortified milk, green leafy vegetables, nuts, etc, are some of the best food sources for calcium. It’s important to note that all foods differ in their calcium content. 

The following tabular representation of recommended daily allowance (RDA) of calcium and calcium content in food has been issued by the NIH – National Institutes of Health, Office of Dietary Supplements, provided by the Dietary Reference Intakes (DRIs), and developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences):  

FoodMilligrams (mg) per serving
Yogurt, plain, low fat415
Orange juice, calcium-fortified349
Mozzarella, part-skim333
Sardines, canned in oil, with bones325
Cheddar cheese307
Milk, nonfat299
Soymilk, calcium-fortified299
Milk, reduced-fat (2% milk fat)293
Yogurt, fruit, low fat258
Salmon, pink, canned, solids with bone181
Cottage cheese, 1% milk fat138
Breakfast cereals, fortified with 10% of the DV for calcium130
Turnip greens, fresh, boiled99
Kale, fresh, cooked94
Ice cream, vanilla84
Chia seeds76
Bread, white73
Bread, whole-wheat30
Broccoli, raw21
Cream cheese, regular14


What Happens When the Calcium Levels in Our Body Are Low?

When calcium levels in the body are below normal, various health issues may appear, such as hypocalcemia, osteoporosis, rickets, osteomalacia, or hypoparathyroidism. 


Due to calcium deficiency, also known as Hypocalcemia, our body may lose its strength, the muscles start to cramp, and tingling in the limbs may occur. In such cases, calcium supplements that increase the amount of calcium in the body are administered in therapies when there’s not enough calcium for strong bones and proper cellular function.

In order for the calcium to be easily absorbed in the human body, it needs the help of vitamin D. This vitamin can be produced in the body by a healthy exposure to sunlight or can be gained from supplements or vitamin D rich foods such as fish oil, orange juice, and other fruit juices, salmon, cheese, eggs, pork chops, and mushrooms.

Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are the two most important supplement forms of this vitamin that are needed for improved bone health. 


Low levels or lack of calcium can trigger demineralization of bones. The bone density is lost, and as a result, osteoporosis may occur. Namely, osteoporosis is a medical condition characterized by the loss of bone density due to calcium deficiency.

Since calcium is the main mineral involved in the formation of the skeletal structure of the body, osteoporosis occurs as a result of the disbalance between the formation of the bone and its resorption – risk factors that ultimately lead to bone loss or easily broken bones.

What Are the Symptoms of Osteoporosis?

While the symptoms may not be easily detectable for many years, the conditions that are experienced by the affected individuals include:

  • Brittle bones that are prone to breaking;
  • Increasing pain in the back;
  • Stooped bodily posture.

A higher risk of osteoporosis may occur due to a low calcium diet, consumption of alcohol, underlying diseases (such as rheumatoid arthritis), genetic heritage, etc.

Rickets and Osteomalacia

Osteomalacia is a medical condition that occurs when the process of mineralization of the unmineralized organic component of bone, i.e. the osteoid, becomes impaired. Similarly, rickets is a condition of impaired calcification of the bones, mainly occurring in children. The symptoms include painful bones, low bone mass, fatigue, unwillingness to walk, as well as deformities of the bones.


Since the parathyroid hormone regulates both the calcium and phosphorus levels in the body, its proper functioning is of vital significance for the homeostatic processes. However, if the parathyroid gland becomes dysfunctional and starts to secrete parathyroid hormone below the normal levels, hypoparathyroidism occurs.

This medical condition leads to decreased levels of calcium in the body, triggering in that way tingling in both the arms and the legs, muscle cramps, decay of teeth, tiredness, disruption of the hormone-related circadian cycles of the body, etc.

Covid-19 and Calcium

The newest research on the highly contagious and fast-spreading Covid-19 virus that caused a pandemic outbreak has given some very informative evidence about the correlation of calcium with this virus. 

Among the many meta-analyses, one of the studies exposed researched the use of nasal calcium-rich salts. According to the findings of this study, the calcium saturated slats have prevented the airborne virus particles from entering the lungs.

The resulting evidence of this research is highly significant regarding the preventive measures undertaken regarding the proper maintenance of personal hygiene during the Covid-19 pandemic. (Get the latest public health information from

The Use of Calcium in Everyday Life

Various forms of calcium have a wide application in many industries. For instance, calcium sulfate (CaSO3.2H2O), calcium silicate (CaO.SiO2), calcium metasilicate (CaO.SiO3), calcium copper silicate (or cuprorivaite), and dolomite, are frequently used for producing coloring pigments, cement, glass, toothpaste, plastic, etc.

Industrial Uses of Calcium

Construction materials, such as cement, brick lime, plaster, glass, paint, paper, sugar, glazes, and concrete, have calcium as one of their main ingredients. Also, the nonferrous alloys can be purified by the use of calcium due to their strong reactions with oxygen and sulfur. Thus, it is used as a deoxidizer, desulphurizer, and decarburizer.

Application of Calcium in the Medical and Pharmaceutical Industries

Calcium Supplementation

Since our bodies are unable to naturally produce calcium, calcium supplements are administered in order to support the function of the nervous system, bone health, muscles, the heart, as well as to strengthen the teeth. According to a study, supplemental calcium intake may also prevent blood clotting, high blood pressure, heart disease, heart attack, prevent osteoporosis in postmenopausal women and older adults, and even some forms of cancer as it regulates cellular activity and cell membrane permeability. In addition, calcium carbonate is used in antacid medicines against heartburn (stomach acid), which improves the health of the gastrointestinal tract. 

There are four main forms of calcium supplements:

  • Calcium carbonate – It contains 40 percent of the elemental form of calcium;
  • Calcium citrate – It contains 21 percent of the elemental form of calcium;
  • Calcium lactate – It contains 13 percent of the elemental form of calcium;
  • Calcium gluconate – It contains 9 percent of the elemental form of calcium.
Recommended Daily Dose of Calcium Supplements

According to a survey from the U.S. Department of Agriculture, the teenagers in the United States are more often replacing the glass of milk with a glass of soft or fizzy drink. For this reason, both boys and girls are advised to take at least 1300 mg of calcium per day, which equals about four and a half eight-ounce glasses of low-fat milk which makes for a daily value of dietary calcium. This measurement meets the daily body needs of calcium in healthy teenagers from nine to eighteen years of age. 

Please consult your healthcare provider prior to taking any type of supplements. 

How Dangerous Is Calcium?

Calcium has no hazardous or toxic effects since it’s a part of our body. This chemical substance also does not burn the skin when it gets in touch with it since it’s less chemically reactive than the other chemical elements. However, in case of accumulation of large amounts of calcium in the bodily tissues, this trace-element can lead to some side-effects, such as constipation, gas, bloating, or even formation of kidney stones and an increased risk of a heart attack. Lactose intolerance can also prevent the absorption of calcium from dairy products. 

Environmental Effects of Calcium

Calcium is present in almost all elements of our surroundings, in many of its forms. Due to the pH regulation property, this alkaline earth metal can regulate the soil’s alkalinity, which is beneficial for plants. The only negative effect it has is when the ‘hard water’ (water enriched with calcium) is used by some of the household appliances. After prolonged use, the appliance may break due to the calcium accumulations that may block the machine’s mechanisms. 

Isotopes of Calcium

There are 26 calcium isotopes that range from 35Ca to 60Ca. Among them,40Ca, 42Ca, 43Ca, 44Ca, and 46Ca are calcium’s stable isotopes with a half-life of 

41Ca is a calcium cosmogenic isotope with a half-life of almost 100,000 years (99,440 years, to be more precise). 

The most characteristic calcium isotope is calcium-40, occurring in 96.94% of all calcium accumulations. 

Nuclide[3]ZNIsotopic mass (Da)[4]


[n 1]



[n 2]




[n 3]




[n 4]

Spin and



[n 5][n 6]

Natural abundance (mole fraction)
Normal proportionRange of variation
35Ca201535.00514(21)#25.7(2) msβ+, p (95.9%)34Ar1/2+#  
β+, 2p (4.1%)33Cl
36Ca201635.99307(4)101.2(15) msβ+, p (51.2%)35Ar0+  
β+ (48.8%)36K
37Ca201736.9858979(7)181.1(10) msβ+, p (82.1%)36Ar3/2+#  
β+ (17.9%)37K
38Ca201837.97631923(21)443.70(25) msβ+38K0+  
39Ca201938.9707108(6)860.3(8) msβ+39K3/2+  
40Ca[n 7]202039.962590866(22)Observationally Stable[n 8]0+0.96941(156)0.96933–0.96947
41Ca202140.96227792(15)9.94(15)×104 yEC41K7/2−Trace[n 9] 
45Ca202544.9561863(4)162.61(9) dβ45Sc7/2−  
46Ca202645.9536880(24)Observationally Stable[n 10]0+4(3)×10−54×10−5–4×10−5
47Ca202746.9545414(24)4.536(3) dβ47Sc7/2−  
48Ca[n 11]202847.95252290(10)(6.4+0.7



−0.9)×1019 a

ββ−[n 12][n 13]48Ti0+0.00187(21)0.00186–0.00188
49Ca202948.95562288(22)8.718(6) minβ49Sc3/2−  
50Ca203049.9574992(17)13.9(6) sβ50Sc0+  
51Ca203150.9609957(6)10.0(8) sβ51Sc(3/2−)  
52Ca203251.9632136(7)4.6(3) sβ (98%)52Sc0+  
β, n (2%)51Sc
53Ca203352.96845(5)461(90) msβ (60%)53Sc3/2−#  
β, n (40%)52Sc
54Ca203453.97299(5)90(6) msβ (93%)54Sc0+  
β, n (7%)53Sc
55Ca203554.98030(32)#22(2) msβ55Sc5/2−#  
56Ca203655.98508(43)#11(2) msβ56Sc0+  
57Ca203756.99262(43)#5# msβ57Sc5/2−#  
β, n56Sc
58Ca203857.99794(54)#3# msβ58Sc0+  
β, n57Sc
59Ca2039  β59Sc   
60Ca2040  β60Sc0+  

Source: Wikipedia

List of Calcium Compounds

Calcium most often forms oxides, silicates, hydrides, and phosphates. The extensive list of calcium compounds consists of the following chemical substances containing molecules of calcium:

  • Alite;
  • Amorphous calcium carbonate;
  • Belite;
  • Bismuth strontium calcium copper oxide;
  • Calcium 2-aminoethylphosphate;
  • Calcium acetate;
  • Calcium alginate;
  • Calcium alpha-ketoglutarate;
  • Calcium aluminates;
  • Calcium aluminoferrite;
  • Calcium aluminosilicate;
  • Calcium ammonium nitrate;
  • Calcium arsenate;
  • Calcium ascorbate;
  • Calcium azide;
  • Calcium benzoate;
  • Calcium bicarbonate;
  • Calcium bisulfite;
  • Calcium borate;
  • Calcium bromate;
  • Calcium bromide;
  • Calcium carbide;
  • Calcium carbonate;
  • Calcium chlorate;
  • Calcium chloride;
  • Calcium chromate;
  • Calcium citrate;
  • Calcium citrate malate;
  • Calcium copper titanate;
  • Calcium cyanamide;
  • Calcium diglutamate;
  • Calcium disilicide;
  • Calcium dobesilate;
  • Calcium erythorbate;
  • Calcium fluoride (fluorite, or fluorspar);
  • Calcium formate;
  • Calcium fructoborate;
  • Calcium fumarate;
  • Calcium glubionate;
  • Calcium glucoheptonate;
  • Calcium gluconate;
  • Calcium glyceryl-phosphate;
  • Calcium guanylate;
  • Calcium hexaboride;
  • Calcium hydride;
  • Calcium hydroxide;
  • Calcium hydroxyphosphate;
  • Calcium hypochlorite;
  • Calcium inosinate;
  • Calcium iodate;
  • Calcium iodide;
  • Calcium lactate;
  • Calcium lactate gluconate;
  • Calcium magnesium acetate;
  • Calcium malate;
  • Calcium monohydride;
  • Calcium monophosphide;
  • Calcium monosilicide;
  • Calcium morphenate;
  • Calcium nitrate;
  • Calcium nitride;
  • Calcium nitrite;
  • Calcium oxalate;
  • Calcium oxide;
  • Calcium pangamate;
  • Calcium perchlorate;
  • Calcium permanganate;
  • Calcium peroxide;
  • Calcium phosphate;
  • Calcium phosphide;
  • Calcium propionate;
  • Calcium pyrophosphate;
  • Calcium selenide;
  • Calcium silicate;
  • Calcium silicate hydrate;
  • Calcium sorbate;
  • Calcium stearate;
  • Calcium stearoyl-2-lactylate;
  • Calcium sulfate (anhydrite, gypsum);
  • Calcium sulfide;
  • Calcium sulfite;
  • Calcium tartrate;
  • Calcium titanate;
  • Calcium(I) chloride;
  • Coccolith;
  • Calcium cyanide;
  • Dicalcium citrate;
  • Dicalcium phosphate;
  • Dodecacalcium hepta-aluminate;
  • Egyptian blue;
  • Friedel’s salt;
  • Lime sulfur;
  • Limewater;
  • Monocalcium aluminate;
  • Monocalcium citrate;
  • Monocalcium phosphate;
  • Octacalcium phosphate;
  • Plaster;
  • Soda lime;
  • Sodium calcium edetate;
  • Tetracalcium phosphate;
  • Thallium barium calcium copper oxide;
  • Tobermorite;
  • Tricalcium aluminate;
  • Tricalcium phosphate.

Calcium Carbonate (CaCO₃)

Calcium carbonate, or calcite, is a non-toxic and odorless white mineral that is found in soft and porous mineral rocks, labeled as chalk. This ionic salt that makes a form of limestone has the chemical formula CaCO₃. Marble is also a form of calcium carbonate. It’s a metamorphic rock made up of dolomite, calcite, and hydrated magnesium silicate (Mg₃Si₄O₁₀(OH), also known as talc. 

Formation of Stalactites and Stalagmites

Stalactites and stalagmites are elongated icicle-like forms of mineral deposits that are typically found in limestone caves. While the stalagmites rise from the cave’s floor, the stalactites stem from the roof of the cavern. They are made of calcite, i.e. calcium carbonate deposits dissolved in the dripping cavern waters that contain carbon dioxide, thus forming calcium bicarbonate, or Ca(HCO3)2.

Lapis Lazuli (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2

The rich dark-blue color sprinkled with golden specks made of pyrite makes this gemstone one of the most desired jewelry stones. Lapis Lazuli presents a mixture of several minerals that includes calcite, pyrite, hauynite, etc. 

The name of the precious mineral is derived from both Latin and Persian words denoting ‘stone of azure’. The Badakhshan area in northern Afghanistan is the location with the greatest lapis lazuli deposits. The oldest mines from where ancient Sumerians and Egyptian pharaohs were obtaining this calcium mineral are also located there. 

5 Interesting Facts And Explanations

  1. After iron and aluminium, calcium is the third most abundant metal found naturally in Earth’s crust.
  2. Calcium carbonate is the most commonly found compound of calcium on Earth. 
  3. The chemical elements hydrogen, oxygen, carbon, and nitrogen are normally found in the human body and are responsible for the maintenance of its functions and homeostasis. However, some of the other elements of the periodic table occur in traces that are just as vitally important for some specific biological functions. Calcium is the most essential and abundant trace-element found in our body. 
  4. The body of a healthy human individual contains approximately one kilogram of calcium. 
  5. While 99% of the calcium deposits in the human body are found in the bones and teeth, there is only 1% of this trace element found in the bloodstream. In this way, it supports the health of the nervous system, the heart, and the muscles.